sound output device

BACKGROUND

Field of the Disclosure

The present disclosure relates to an audio system, a method for sound reproduction, an audio signal source device, and a sound output device.

Description of Related Art

Today's multichannel audio or surround sound systems usually consist of a central sound decoding unit for decoding a digital surround sound signal into individual analog sound signals and assigning the individual analog sound signals to a plurality of active (with amplifier) or passive (without amplifier) speakers. These speakers are connected to the sound decoding unit by individual speaker cables. Currently, 5.1 or 7.1 systems are very popular. For example, a 5.1 surround sound system comprises five main channels (a left front channel, a front right channel, a center channel and two surround channels for rear left and rear right speakers) and one low-frequency effects (subwoofer) channel.

A disadvantage of such surround sound systems is the large number of required cables, which may cause some disarray in the living room: In addition to the cables connecting the individual speakers to the sound decoding unit the sound decoding unit (audio signal source device) and the speakers of the audio system may be connected to the mains by power cables.

SUMMARY

The invention is concerned with providing an improved multichannel audio system.

The invention solves this problem with a system according to claim 1 , a method according to claim 10, an audio signal source device according to claim 12 and a sound output device according to claim 15. An audio system in a home network is provided, comprising an audio signal source device connected to the home network to a plurality of sound output devices and configured to transmit a digital audio stream including digital audio data for a plurality of audio channels to the sound output devices. Each of the sound output devices comprises a decoder configured to decode the digital audio stream in order to derive an audio channel of the plurality of audio channels, wherein the audio channel is associated with the respective sound output device. Each sound output device is configured to output its respective associated audio channel, and the outputs of the sound output devices are synchronized by delaying them by sound output device-specific delays.

A method for sound reproduction is described, comprising: transmitting, by an audio signal source device via a home network, a digital audio stream including digital audio data for a plurality of audio channels; and decoding the digital audio stream by a plurality of sound output devices in order to derive an audio channel of the plurality of audio channels, the audio channel being associated with the respective sound output device. The method further comprises outputting, by each of the sound output devices, its respective associated audio channel, wherein the outputs of the sound output devices are synchronized by delaying them by sound output device-specific delays. An audio signal source device is provided, comprising: a first transmitter configured to transmit a digital audio stream including digital audio data for a plurality of audio channels; and a second transmitter configured to transmit a digital audio calibration signal. The audio signal source device further comprises a microphone input configured to receive a calibration sound signal corresponding to the digital audio calibration signal; and a controller to determine a delay based on a time difference between transmitting the digital audio calibration signal and receiving the calibration sound signal.

A sound output device is described, comprising: a receiver configured to receive a delay information for said sound output device; and a memory configured to store the delay information. The sound output device further comprises: a decoder to decode a digital audio stream; and an output unit configured to output a sound of an audio channel. The audio channel is associated with said sound output device and the output is delayed by a sound output device-specific delay derived from the delay information. The foregoing paragraphs have been provided by way of general introduction, and are not intended to limit the scope of the following claims. The described embodiments, together with further advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings. The elements of the drawings are not necessarily to scale relative to each other.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

Fig. 1 is a schematic representation of an audio system according to an embodiment of the present invention showing an audio signal source device comprising a delay unit and a plurality of sound output devices connected to a home network; Fig. 2 is a schematic representation of an audio system according to an embodiment of the present invention showing an audio signal source device and a plurality of sound output devices connected to a home network, each comprising a delay unit;

Fig. 3 is a schematic representation of an audio system according to an embodiment of the present invention showing an audio signal source device comprising a delay unit and a plurality of sound output devices connected to a home network, wherein one of the sound output devices controls two speakers;

Fig. 4 is a schematic representation of an audio system according to an embodiment of the present invention showing an audio signal source device and a plurality of sound output devices connected to a home network, each comprising a delay unit, wherein one of the sound output devices controls two speakers;

Fig. 5 is a schematic representation of an audio system according to an embodiment of the present invention showing an audio signal source device comprising a delay unit and a plurality of sound output devices connected to a home network, wherein a microphone array may be connected to a microphone input of the audio signal source device;

Fig. 6 is a schematic flowchart of a method for sound reproduction that can be carried out for example by the audio signal source device of the embodiment of Fig. 1 , according to an embodiment of the present invention; Fig. 7 is a schematic flowchart of a method for sound reproduction that can be carried out for example by each of the sound output devices of the embodiment of Fig. 2, according to an embodiment of the present invention; and Fig. 8 is a schematic representation of a FIFO buffer storage that can be included in a sound output device, according to an embodiment of the present invention.

Fig. 9 shows an exemplary power line communication (PLC) network as example for a home network with a plurality of devices connected to the network.

DESCRIPTION OF THE EMBODIMENTS

The invention reduces the number of required cables by using a home network to connect an audio signal source device to a plurality of sound output devices.

Fig. 9 shows an exemplary configuration of a home network as it can be applied in a home of a family, for example. The home network shown in Fig. 9 is a power line communication (PLC) network with a plurality of devices connected to the network via a power line 902 of the house. The power line 902 may be used to provide electric power to the devices.

An advantage of PLC over wireless solutions is, that a wireless solution (e.g., WiFi) may suffer from insufficient coverage. Further, PLC provides broadband coverage in solid-wall households without the requirement of installing new wires. Further, PLC may be used as in- home backbone media, complementary to wireless communication. Hence, PLC offers a high comfort/convenience factor to the user.

In Fig. 9, each of the devices may be connected to the power line 902 via a socket 904. For transmitting and receiving data packets over the power line 902 via PLC, each device may comprise a transmitter and/or a receiver, for example, in the form of a PLC modem. In Fig. 9, a plurality of different devices is exemplarily shown. However, the devices connectable to a PLC network are not limited to the ones shown in Fig. 9 and several other devices may be connected to a PLC network. For example, as shown in Fig. 9, a television apparatus 950 may be connected to the PLC network via a socket 904 and a PDA 952 may be wirelessly connected via a wireless modem 954 connected to the PLC network via a socket 904. Further, a baby monitor system 956 and a personal computer 958 may be connected to the PLC network. An audio system 960 may be connected to the PLC network, wherein the audio system 960 may be an audio system as described in the following specification. Thus, the audio system 960 may comprise a plurality of sound output devices all connected to the power line 902 via a socket 904. Further, an audio signal source device may be part of the audio system 960, wherein the audio signal source device transmits a multichannel digital audio stream to the plurality of sound output devices (e.g., the speakers shown in Fig. 9).

Further, an audio/video home server 962 and a plurality of gaming devices 964 may be connected to the PLC network. The audio/video home server 962 may be used, for example, as an audio signal source device for the audio system 960. Further, one of the gaming devices 964 may be used as audio source or as audio signal source device for the audio system 960. A security camera 966 and an electric vehicle 968 may be connected to the PLC network. The power line 902 may also be used for smart grid and/or smart energy applications, such as demand side management for household appliances, wherein smart grid signals may be transmitted to the plurality of connected devices via the PLC. Further, the PLC network may be connected to the Internet 970, such that, for example, the personal computer 958 and the gaming devices 964 may have access to the Internet 970. The baby monitor system 956 and the security camera 966 may transmit a video signal via PLC to the personal computer 958 and/or to the Internet 970, for example. Further, the PDA 952 may communicate with the Internet 970 and the gaming devices 964 may communicate with each other via PLC. An audio signal source device of the audio system 960 may transmit a digital audio stream to the plurality of sound output devices.

If a plurality of devices communicates over the same PLC network, collisions may happen, retransmissions may occur and jitter may be generated. Hence, the transmission time of the data packets may be longer than in the case of a direct connection or in the case that the PLC is only used by one application. Therefore, a synchronization of the individual play-outs of the speakers of the audio system 960 may be required in order to achieve a synchronized play-back of all the channels of the digital audio stream.

When replacing the cables of a conventional multichannel audio system by a home network (e.g., WiFi or power line communication, PLC), the speakers should be synchronized to guarantee a simultaneous audio play-out. Synchronization requirements are very hard for cost sensitive consumer electronic devices. The analog sound play-out of individual speakers has to be synchronized preferably to a precision of a few microseconds. If this precise synchronization is not guaranteed the analog play-out signals are affected by phase modulations. When a persons listens to such signals affected by jitter, this results in the impression of moving speakers. Hence, sound quality might be reduced. A simple calculation might illustrate the necessity of synchronization: If sound is transported in the air by 300 m/s it takes 30 cm per ms, 3 cm per 100 μβ or 3 mm per 10 \is. In a home network, which is shared by multiple applications like web-browsing, watching video transmissions, voice over I P (VoIP), remote control of heating, window shutters, etc, packet collisions might happen. In the case of a Homeplug AV PLC Home network packet retransmissions are necessary in the case of data collisions, burst noise or channel changes. Here, in the worst case the Extended Inter Frame Spacing (EIFS) time has to be awaited for potential retransmissions. The EI FS might last up to 2.9 ms. In such a case this would result in the consumer's impression that one of the speakers of the surround sound system might move by almost up to 1 m. In most living rooms the impression of such a moving speaker will cause reduced audio quality. If the speaker system is addressed by a - from a timing point of view - non-synchronized home network the surround sound experience is limited.

Performing such a precise synchronization in conventional audio systems requires expensive additional components for time-stamping of packets, defining extra priorities in handling of the data packets, precise clocks at all nodes, etc. These additionally required components are expensive in a consumer electronic home network.

The present invention provides an audio system and a method for synchronizing said audio system that can be easily carried out without the need of expensive additional components.

In the embodiments, each sound output device (controlling a speaker) may be equipped with a multichannel surround sound decoder. Thus, the entire digital audio stream including digital audio data for a plurality of audio channels may be transmitted to at least one or each sound output device, where it is decoded and a sound for the respective speaker is outputted. If there is a constant delay time between transmitting the digital audio stream and outputting a channel of the stream by a specific sound output device, this delay time only has to be determined once, for example, when the audio system is set up or each time a new device is added to the PLC network or removed from the PLC network. During playback, a sound output device-specific delay may be applied to each channel. Since all sound output devices may receive the same entire multichannel digital audio stream, no expensive and elaborate timing has to be performed amongst the speakers. In the following, a digital audio stream including digital audio data for a plurality of audio channels is also referred to as a "digital audio stream". Further, the "predetermined delay" might be referred to as "sound output device-specific delay".

Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, Fig. 1 shows an audio system according to an embodiment of the present invention.

An audio signal source device 100 may be connected to a power line via a socket 104. The power line 102 provides the audio signal source device 100 with electric power and is also configured to be used in a power line communication (PLC) network. The audio signal source device 100 may comprise a Blu-ray Disc™ player, a DVD player, a television apparatus, a Dolby Digital™ surround sound receiver, or a personal computer, for example.

Further, a plurality of sound output devices 106 may be connected to the power line 102 via a plurality of sockets 104. Each of the sound output devices 106 may drive a speaker 108a- 108e by outputting an amplified analog audio signal.

In a 5.1 surround sound audio system, five speakers may be provided: a center speaker 108a, a front left speaker 108b, a front right speaker 108c, a rear left speaker 108d, and a rear right speaker 108e. Further, a subwoofer speaker may be provided for low frequency bass sounds. Each speaker 108a-108e may be connected to a respective sound output device 106 via a cable and at least one or each one of the speakers 108a-108e may be provided integrally with a corresponding one of the sound output devices 106, for example in a same housing.

Each one of the sound output devices 106 may be connected to the power line 102 via a socket 104. The power line 102 provides the sound output devices 106 with electric power and may also be configured to be used in a power line communication (PLC) network for communication between the audio signal source device 100 and the sound output devices 106.

The audio signal source device 100 comprises a multichannel audio signal source 1 10 that may be for example an audio signal source of a Blu-ray Disc™ player, a DVD player, a radio station, a TV receiver audio source, an HDMI audio signal source, an internet audio signal source or any other multichannel audio signal source outputting a digital audio stream including digital audio data for a plurality of audio channels. The audio signal source 1 10 may be a 5.1 , 7.1 or any other surround sound signal source or a stereo sound signal source, wherein the stereo sound signal might have been converted to a 5.1 or 7.1 surround sound signal (digital audio stream).

The digital audio stream including digital audio data for a plurality of audio channels may be fed from the audio signal source 1 10 into a decoder 1 12. The decoder may be a surround sound decoder decoding the digital audio stream into a plurality of digital single audio channel signals, wherein at least one or each one of the digital single audio channels is designated for a respective one of the speakers 108a-108e. The delay units 1 14 may be provided in the audio signal source device for applying a predetermined delay (sound output device-specific delay) to at least one of the digital single audio channel signals provided by the decoder 1 12 and a plurality of individually delayed digital single audio channel signals may be outputted. A delay information may be stored in a memory 1 1 6 of the audio signal source device 100. The delay information may comprise information on the predetermined delays that are applied to the plurality of digital single audio channel signals, respectively. Thus, the predetermined delay applied to a digital single audio channel signal is derived by the delay information stored in the memory 1 16. An encoder 1 18 encodes the delayed digital single audio channel signals back into a delayed digital audio stream, for example into a 5.1 surround sound audio signal. The audio signal source device 100 further comprises a transmitter 120 for transmitting the delayed digital audio stream over the power line 102. Hence, the audio signal source device 100 is configured to transmit a digital audio stream including digital audio data for a plurality of audio channels. The transmitter 120 may be a PLC modem for sending digital data packets via power line communication (PLC) to the sound output devices 106. Thus, the entire delayed digital audio stream including digital audio data for a plurality of audio channels may be sent to at least one of the sound output devices 106 over the power line 102. Besides the digital audio stream, a plurality of other instructions might be sent to the sound output devices 106. This holds for all embodiments of the present invention described in this application. For example, instructions for adjusting the audio volume and/or for selecting an audio channel might be sent to the sound output devices 106. Further, control information for a decoder might be sent by the transmitter 120 of the audio signal source device 100.

The audio signal source device 100 further comprises a controller 122 for controlling the audio signal source device 100. The controller 122 may comprise a CPU processor or any other controlling circuit configured to control the functionality of the audio signal source device 100 including the audio signal source 1 10, the decoder 112, the delay units 1 14, the memory 1 16, the encoder 1 18, and the transmitter 120. The audio signal source device 100 further comprises a microphone input 124 to which a microphone 126 may be connected via a microphone cable. The microphone 126 is configured to receive sound signals (e.g., a calibration sound signal) from the speakers 108a-108e and to transmit these sound signals to the microphone input 124 of the audio signal source device 100. These sound signals may be processed by the controller 122 of the audio signal source device 100 and used to determine the predetermined delay for at least one or each one of the speakers 108a- 108e.

In the following, one of the five sound output devices 106 shown in Fig. 1 is described exemplarily. The sound output devices 106 controlling the speakers 108a-108e located at different positions, all have a substantially similar configuration. An audio channel of the digital audio stream is associated with at least one of the sound output devices 106.

The sound output device 106 receives the ^' delayed digital audio stream including a plurality of audio channels with a receiver 128. The receiver 128 may be a PLC receiver or PLC modem for receiving a power line communication (PLC) signal sent from the transmitter 120 of the audio signal source device 100 over the power line 102. The sound output device 106 further comprises a decoder 130 for decoding the digital audio stream. The decoder 130 may be a surround sound decoder decoding the received digital audio stream into a plurality of individually delayed digital single audio channel signals or at least into the one digital single audio channel signal which is associated with the respective speaker 108a-108e driven by the sound output device 106. For example the decoder 130 of the sound output device 106 of the center speaker 108a may only decode and/or only output the digital single audio channel signal associated with the center speaker 108a.

A digital-to-analog converter (DAC) 132 converts the digital single audio channel signal for the respective speaker 108a-108e into an analog sound signal. The analog sound signal may be amplified by an amplifier 134 (output unit) and outputted to the corresponding speaker 108a-108e via a speaker cable. Accordingly, for example, the center speaker 108a gives out a center channel sound signal, to which a corresponding predetermined delay has been applied by the delay unit 1 14 of the audio signal source device 100. Speakers 108a- 108e might also be embedded into the sound output device 106. In all embodiments, the sound output device 106 may derive audio volume information from the received data stream. This information might be used to set an amplification level of the amplifier 134. By applying an individual delay to the respective digital single audio channel signals, a listener located at a position near the microphone 126 can obtain a synchronized listening experience. The determining of the individual predetermined delay is described below.

Fig. 2 shows an embodiment in which a predetermined delay may be applied to the plurality of audio channels on the receiver side (in the sound output devices 206) and not on the transmitter side (in the audio signal source device 200) as described above in the embodiment of Fig. 1 .

In the embodiment of Fig. 2, an audio signal source device 200 may be connected to a power line 202 via a socket 204. Also connected to the power line 202 via a plurality of sockets 204 are a plurality of sound output devices 206 each driving a corresponding speaker 208a-208e.

The audio signal source device 200 shown in Fig. 2 comprises a multichannel audio signal source 210 similar to the one described in the embodiment of Fig. 1 . The audio signal source 210 outputs a digital audio stream, which may be transmitted by a transmitter 220 into the power line 202 via power line communication (PLC). The undelayed digital audio stream including digital audio data for a plurality of audio channels may be transmitted into the power line 202 to the plurality of sound output devices 206. Thus, the audio signal source device 200 is configured to transmit a digital audio stream including digital audio data for a plurality of audio channels.

The audio signal source device 200 further comprises a controller 222 for controlling the audio signal source device 200 including the audio signal source 210 and the transmitter 220. The controller 222 may be similar to the controller 122 provided in the embodiment of Fig. 1 , for example, the controller 222 may comprise a CPU. A microphone input 224 may be provided for connecting a microphone 226 to the audio signal source device 200. The controller 222 may determine a predetermined delay (sound output device-specific delay) for at least one of the plurality of audio channels. The controller 222 may further generate delay information from which the predetermined delay for the respective speakers 208a-208e can be derived. The delay information may be transmitted by the transmitter 220 via the power line 202. Hence, in the embodiment of Fig. 2, the transmitter 220 transmits the undelayed digital audio stream into the power line 202 and transmits the delay information into the power line 202. The delay information for the respective speakers 208a-208e may be permanently transmitted into the power line 202 (with short time intervals in between) or may be infrequently transmitted, for example every time when the audio signal source device 200 is powered on, or when a certain configuration process of the audio system is carried out, or when one of the sound output devices 206 sends a request signal to the audio signal source device 200.

In the following, one exemplary sound output device 206 is described, for example the sound output device 206 controlling the central speaker 208a. A receiver 228 of the sound output device 206 receives the digital audio stream. The digital audio stream may be decoded by a decoder 230 into a plurality of digital single audio channel signals or at least into the one digital single audio channel signal which is associated with the respective speaker 208a- 208e. For example, the decoder 230 of the sound output device 206 of the center speaker 208a may only decode and/or only output the digital single audio channel signal associated with the center speaker 208a. The digital single audio channel signal of the respective speaker may be led into a delay unit 214 of the corresponding sound output device 206. In the delay unit 214 a predetermined delay may be applied to the digital single audio channel signal and a delayed digital single audio channel signal may be outputted.

The receiver 228 of the sound output device 206 may further be configured to receive delay information sent from the audio signal source device 200 over the power line 202. The sound output device 206 comprises a memory 216 to store the delay information associated with the respective speaker 208a-208e. Thus, for example, the memory 216 of the sound output device 206 controlling the center speaker 208a stores delay information on the predetermined delay associated with the center speaker 208a, that is, the delay time that shall be applied to the digital single audio channel signal corresponding to the center speaker 208a. The predetermined delay can be derived from the delay information stored in the memory 216.

The delay unit 214 receives the delay information from the memory 216 and applies the predetermined delay to the respective digital single audio channel signal and outputs a delayed digital single audio channel signal. A digital-to-analog converter DAC 232 converts the delayed digital single audio channel signal into an analog audio signal. This analog audio signal may be amplified by an amplifier 234 of the sound output device 206 and outputted to a speaker 208a-208e connected to the sound output device 206 via a speaker cable. Speakers 208a-208e might also be embedded into the sound output device 206. In the embodiment of Fig. 2, at least one or each one of the sound output devices 206 may apply a predetermined delay to a corresponding channel of the digital audio stream sent by the audio signal source device 200 over the power line 202. Therefore, the audio signal source device 200 can transmit the digital audio stream as it is outputted by the audio signal source 210 without applying a delay. The predetermined delay may be applied to the respective channels at the receiver side, that is, in the sound output devices 206. Therefore, a delay information for at least one of the channels may be sent from the audio signal source device 200 to the sound output devices 206, where it may be stored in a memory 216.

Alternatively, in all embodiments described in this application, the delay information may be transmitted over a communication path different to the one over which the digital audio stream is transmitted. For example, when PLC is used as means for transmitting the digital audio stream, as shown in Fig. 2, the delay information may be transmitted via a different communication path than PLC, for example wirelessly via WiFi, Bluetooth, or infrared communication (e.g., IrDA). The delay information may also be manually inputted into the sound output devices 206 via a user interface.

Further, in all embodiments, the PLC may be replaced by any other home network or communication network capable of transmitting the digital audio stream from the audio signal source device 100, 200 to the sound output devices 106, 206. For example, instead of power line communication, wireless communication may be used. For example, WiFi or Bluetooth may be used to transmit the digital audio stream to the sound output devices 106, 206. Further, for example a local area network (LAN) or the Internet may be used for transmitting the digital audio stream. For example in the case that the PLC of Fig. 1 is replaced by WiFi communication, a WiFi transmitter may be used as transmitter 120 and a WiFi receiver may be used as receiver 128 and antennas may be provided for communicating between transmitter 120 and receiver 128. In the embodiments described in this application, the amplifier 134, 234 is an output unit outputting a sound of an audio channel to a respective speaker 108a-108e, 208a-208e. However, in all embodiments described herein, the amplifier 134, 234 may be omitted in the sound output devices 106, 206. In this case, the sound output devices 106, 206 may comprise a sound output (output unit) and a separate active speaker may be connectable to the sound output (output unit) via a TRS connector, for example. Now referring to Fig. 3, a configuration similar to the one shown in Fig. 1 is described. The predetermined delay is also applied at the sender side (in the audio signal source device 300). In Fig. 3, the audio signal source device 300 and the sound output devices 306 controlling the center speaker 308a, the front left speaker 308b, and the front right speaker 308c may be identical to the ones described with reference to Fig. 1 . Hence, the functionality of these elements will not be repeated in detail.

As in the embodiment of Fig. 1 , the audio signal source device 300 may comprise an audio signal source 310 for outputting a digital audio stream, a decoder 312 for decoding the digital audio stream to a plurality of digital single audio channel signals, delay units 314 for applying a predetermined individual delay to at least one of the digital single audio channel signals, a memory 316 for storing a delay information, an encoder 318 for encoding the plurality of individually delayed digital single audio channel signals to a digital audio stream, and a transmitter 320 for transmitting the digital audio stream via PLC into the power line 302. The audio signal source device 300 further comprises a controller 322 for controlling the audio signal source device 300, and a microphone input 324 to which a microphone 326 can be connected.

The audio signal source device 300 may be connected to the power line 302 via a socket 304. Also connected to the power line 302 via sockets 304 are a plurality of sound output devices 306.

Each of the sound output devices 306 for the two front speakers 308b, 308c and the center speaker 308a may comprise a receiver 328 for receiving the delayed digital audio stream, a decoder 330 for decoding the delayed digital audio stream, a DAC 332 for converting a specific one of the digital single audio channel signals into an analog audio signal, and an amplifier 334 for amplifying the analog audio signal. The amplified analog audio signal may be outputted to a speaker 308a-308c. Only one sound output device 306a may be provided for the two rear speakers 308d, 308e. Similar to the other sound output devices 306, the sound output device 306a comprises a receiver 328a for receiving the digital audio stream transmitted by the audio signal source device 300. The digital audio stream may be decoded by a decoder 330a into a plurality of digital single audio channel signals. Two of these digital single audio channel signals are further processed, namely the one associated with the rear left speaker 308d and the one associated with the rear right speaker 308e. The digital single audio channel signal for the rear left speaker 308d may be fed into a DAC 332a, where it may be converted into an analog signal. The analog signal for the rear left speaker 308d may be amplified by an amplifier 334a and outputted to the rear left speaker 308d. The digital single audio channel signal for the rear right speaker 308e may be fed into a DAC 332b, where it is converted into an analog signal. The analog signal for the rear right speaker 308e may be amplified by an amplifier 334b and outputted to the rear right speaker 308e.

By using only one sound output device 306a for two speakers 308d, 308e, the required amount of sound output devices 306, 306a can be reduced and thereby the required amount of devices connected to sockets 304 can be reduced. For example in a home cinema environment, the distance between the two rear speakers 308d, 308e may be much smaller than the distance of one of the rear speakers 308d, 308e to one of the front speakers 308b, 308c. Hence, it might be advantageous to connect the sound output device 306a for the rear speakers 308d, 308e to one socket 304 in the back of the room and the sound output devices 306 of the other speakers 308a-308c to other sockets 304 in the front of the room. Alternatively, also the control of other speakers 308a-308e may be combined as shown for the rear speakers 308d, 308e in Fig. 3. For example, one single sound output device may be provided for the two front speakers 308b, 308c, and for the center speaker 308a. Alternatively, for example, a sound output device may be provided in the housing of a subwoofer and may be configured to control a subwoofer speaker, the two front speakers 308b, 308c, and the center speaker 308a, for example.

Fig. 4 shows an embodiment in which the predetermined delay is added to the audio channels by delay units 414, 414a in the sound output devices 406, 406a, and in which the control of the two rear speakers 408d, 408e is combined in one single sound output device 406a connected to the power line 402.

Again, since the audio signal source device 400 and the sound output devices 406 for the center 408a and the front speakers 408b, 408c may be similar to the respective elements of the embodiment of Fig. 2, these elements are only briefly described in the following.

As in the embodiment of Fig. 2, the audio signal source device 400 comprises an audio signal source 410 for outputting a digital audio stream and a transmitter 420 for transmitting the digital audio stream via PLC into the power line 402. The audio signal source device 400 further comprises a controller 422 for controlling the audio signal source device 400, and a microphone input 424 to which a microphone 426 can be connected. The audio signal source device 400 may be connected to the power line 402 via a socket 404. Also connected to the power line 402 via sockets 404 are a plurality of sound output devices 406.

Each of the sound output devices 406 for the two front speakers 408b, 408c and the center speaker 408a may comprise a receiver 428 for receiving the digital audio stream, a decoder 430 for decoding the digital audio stream, a delay unit 414 for applying a predetermined delay to a specific one of the digital single audio channel signals, a DAC 432 for converting the delayed digital single audio channel signal into an analog audio signal, and an amplifier 434 for amplifying the analog audio signal. The amplified analog audio signal may be outputted to a speaker 408a-408c. The sound output device 406 further comprises a memory 416 for storing a delay information. The predetermined delay can be derived from the delay information stored in the memory 416.

Further, only one sound output device 406a is provided for the two rear speakers 408d, 408e. Similar to the other sound output devices 406, the sound output device 406a comprises a receiver 428a for receiving the digital audio stream transmitted by the audio signal source device 400. The digital audio stream may be decoded by a decoder 430a into a plurality of digital single audio channel signals. Two of these audio channel signals are further processed, namely the one associated with the rear left speaker 408d and the one associated with the rear right speaker 408e.

These two digital single audio channel signals may be fed into a delay unit 414a, where a predetermined delay may be applied to at least one of the digital single audio channel signals. A delay information on the predetermined delay for the two audio channels corresponding to the two rear speakers 408d, 408e may be stored in a memory 416a. The delay information may be transmitted by the transmitter 420 of the audio signal source device 400 and received by the receiver 428a of the sound output device 406a. The predetermined delay for the respective audio channels can be derived from the delay information.

The delayed digital single audio channel signal for the rear left speaker 408d may be fed from the delay unit 414a into a DAC 432a, where it is converted into an analog signal. The analog signal for the rear left speaker 408d may be amplified by an amplifier 434a and outputted to the rear left speaker 408d. The delayed digital single audio channel signal for the rear right speaker 408e may be fed from the delay unit 414a into a DAC 432b, where it is converted into an analog signal. The analog signal for the rear right speaker 408e may be amplified by an amplifier 434b and outputted to the rear right speaker 408e.

Fig. 5 shows that the microphone 126, 226, 326, 426 of the embodiments of Figs. 1-4 can be replaced by a microphone array 526. The microphone array 526 comprises a plurality of microphones 526a provided at different locations of the microphone array 526. The distances and orientation of the different microphones 526a of the microphone array 526 may be known to the audio signal source device 500. For example, four microphones 526a may be provided as a rectangular microphone array 526. The microphone array 526 may further comprise a marking 526b that may comprise, for example, an arrow. Further, a form of a housing of the microphone array 526 may have a preferential direction that enables a user to arrange the microphone array 526 in a certain orientation with respect to the speakers 508a- 508e. For example, an arrow may be provided that shall be pointed in the direction of the center speaker 508a.

The audio system shown in Fig. 5 further comprises an audio signal source device 500 connected via a socket 504 to a power line 502 and a plurality of sound output devices 506 connected via sockets 504 to the power line 502. The audio system of Fig. 5 further comprises a plurality of speakers 508a-508e respectively connected by speaker cables to the sound output devices 506. The speakers 508a-508e might also be embedded into the sound output devices 506.

The audio signal source device 500 comprises an audio signal source 510, a decoder 512, a delay unit 514, a memory 516, an encoder 518, a transmitter 520, a controller 522, and a microphone input 524 to which the microphone array 526 may be connected. Each sound output device 506 may comprise a receiver 528, a decoder 530, a DAC 532, and an amplifier 534.

Except the microphone array 526, all elements of the audio system of Fig. 5 may be the same as the elements of the audio system of the embodiment of Fig. 1 and they may have the same functionality as described above. Further, also in the embodiments of Figs. 2-4, the microphone 226, 326, 426 may be replayed by a microphone array as the one shown in Fig. 5 and described above. An advantage of using the microphone array 526 is that during a calibration process, the controller 522 of the audio signal source device 500 may determine the position of any one of the speakers 508a-508e by a time difference between a detection of a calibration sound signal sent out by the speaker 508a-508e by one of the microphones 526a and another one of the microphones 526a of the microphone array 526. The calibration process will be described in detail below. Fig. 6 shows a method that may be carried out, for example, by the audio signal source device 100, 300, and 500 of the embodiments shown in Figs. 1 , 3, and 5. At S600, a surround sound data stream is decoded. For example, the surround sound data stream (digital audio stream) provided by the audio signal source 1 10, 310, 510 may be decoded by the decoder 1 12, 312, 512. At S602, an individual delay (predetermined delay) may be applied for at least one of the speakers. For example, the delay unit 114, 314, 514 applies a predetermined delay to at least one of the digital single audio channel signals provided by the decoder 112, 312, 512 and corresponding to a respective one of the speakers 108a- 180e, 308a-380e, 508a-580e. At S604, all channels are encoded. For example, the encoder 1 18, 318, 518 encodes the plurality of delayed digital single audio channel signals to one delayed digital audio stream. At S606, all audio channels may be broadcasted to all speakers. For example, the transmitter 120, 320, 520 transmits the delayed digital audio stream into the power line 102, 302, 502. From the power line 102, 302, 502, the delayed digital audio stream may be received by each of the sound output devices 106, 306, 506 corresponding to a respective one of the speakers 108a-180e, 308a-380e, 508a-580e.

Fig. 7 shows a method that may be carried out, for example, by the sound output devices 206, 406 of the embodiments shown in Figs. 2 and 4. At S700, a surround sound data stream is received. For example, the receiver 228, 428 receives the digital audio stream transmitted by the audio signal source device 200, 400. At S702, the surround sound data stream is decoded. For example, the decoder 230, 430 decodes the digital audio stream provided by the receiver 228, 428. At S704, an individual delay (predetermined delay) may be applied to the audio channel of the respective speaker. For example, the delay unit 214, 414 applies a predetermined delay to the digital single audio channel signal associated with the respective speaker 208a-208e, 408a-408e. At S706, a sound of the audio channel of the respective speaker is outputted. For example, the amplifier 234, 434 may output a sound of the audio channel of the respective speaker 208a-208e, 408a-408e.

Fig. 8 shows a First In, First Out (FIFO) buffer storage 802 that may be included in any one of the sound output devices 106, 206, 306, 406, 506 of the embodiments shown in Figs. 1 -5 at a position in the data stream after the receiver 128, 228, 328, 428, 528. The FIFO buffer storage 802 receives incoming data packets 800 from the home network (for example from the PLC network) at a time t(in) and outputs data packets 804 to the decoder at a time t(out). The FIFO buffer storage 802 may be configured to store a section of the digital audio stream.

The timings might also be processed in an enhanced way: If the receiver (sound output device) knows that the signal source 1 10, 210, 310, 410 or 510 outputs the data with a constant rate, the play-out of the data at 132, 232, 332, 432 or 532 shall also be adapted to this constant rate. If the individual transmissions via the home network jitter or are delayed the buffer storage might buffer the data to guarantee a constant play-out. When the broadcasted data packets including the digital audio stream arrive at a sound output device 106, 206, 306, 406, 506 at a time t(in) this time stamp may be used to synchronize the play-out. In the case that different components (for example cheap and expensive components) are used in the different sound output devices 106, 206, 306, 406, 506 and/or speakers 108a-108e, 208a-208e, 308a-308e, 408a-408e, 508a-508e of one audio system, the oscillators in all speakers may not run exactly at the same frequency. During a long play-out session (e.g. a 90 min movie) the processing in the individual sound output devices 106, 206, 306, 406, 506 might scatter. Since the data packets may be broadcasted a packet should arrive at the same time t(in) at all sound output devices 106, 206, 306, 406, 506. This time t(in) might be used to synchronize the play-out time of the speakers 108a-108e, 208a-208e, 308a-308e, 408a-408e, 508a-508e.

If data packet jitter (caused by e.g., delay, collisions, or retransmissions) occurs on the home network to the broadcasted digital audio stream, all individual digital single audio channel signals are affected simultaneously. This leads to a common delay for all digital single audio channel signals, but not to an individual impact on a single channel of the audio signal. If the data rate delivering the sound output devices 106, 206, 306, 406, 506 varies and a constant play-out rate shall be guaranteed, a buffering of the play-out data might be implemented to guarantee a constant play-out in between the individual speakers, even if there is some delay in the stream from the audio signal source device 100, 200, 300, 400, 500.

Additional it might be required to ensure that e.g., the video playback is synchronous with the audio playback. However, human listening impression is more tolerant against a constant delay of all speakers compared to individual delays between different speakers. The individual sound output devices may decode the digital audio stream at each location with a constant reproducible processing time of each decoding process. In the following, a calibration process is described. The calibration process may be carried out by the audio systems of the embodiments shown in Figs. 1-5. The calibration process may be used to determine the predetermined delay for the different audio channels associated with the different speaker positions.

Due to different distances from the respective speakers to a listener's position (for example, corresponding with the position of the microphone 126, 226, 326, 426, 526) and due to different processing times of the sound output devices 106, 206, 306, 406, 506, the digital audio stream broadcasted from the audio signal source device 100, 200, 300, 400, 500 may arrive at different times at the listener's position if no predetermined delay is applied to the channels. Accordingly, the sound signal might be unsynchronized if no predetermined delay is applied.

In order to synchronize the digital audio stream and in order to achieve a perfect calibrated listening experience at the listener's position, predetermined delay times may be applied to the respective channels. For example, in the case of Fig. 1 , if the rear right speaker 108e is provided far away from the listener's position (corresponding with the microphone 126 position), and the center speaker 108a is provided close to the listener's position, and a processing time of the corresponding sound output devices 106 is equal, a predetermined delay for the channel of the center speaker 108a should be larger than a predetermined delay for the channel of the rear right speaker 108e, in order to compensate for the different transit times of the sound. Further, if the two front speakers 108b, 108c are located at an equal distance to the listener's position 126, but a processing time of the receiver 128 of the sound output device 106 for the front left speaker 108b is much larger than the processing time of the receiver 128 of the sound output device 106 of the front right speaker 108c, a predetermined delay for the channel of the front right speaker 108c should be larger than a predetermined delay for the channel of the front left speaker 108b, in order to compensate for the different processing times of the receivers 128. The calibration process may be carried out as follows, wherein the steps are not necessarily in chronological order.

In a first step, the audio signal source device 100, 200, 300, 400, 500 initiates a calibration sound signal for a first speaker of the audio system (for example the center speaker 108a, 208a, 308a, 408a, 508a). In a second step, a digital audio calibration signal comprising the calibration sound signal for the first speaker may be transmitted by the transmitter 120, 220, 320, 420, 520 into the communication network (for example the PLC shown in Figs. 1-5). In a third step, the digital audio calibration signal may be decoded and the first speaker may output the calibration sound signal while all other speakers are silent. The calibration sound signal may be received by the audio signal source device 100, 200, 300, 400, 500 using the microphone 126, 226, 326, 426 or the microphone array 526. Therefore, the microphone 126, 226, 326, 426 or the microphone array 526 should be located at a preferred listener's position, for example on a couch in front of a television apparatus.

In a fourth step, if only one microphone 126, 226, 326, 426 is used, the user may have to define the location of the first speaker via a user input interface of the audio signal source device 100, 200, 300, 400. This step may be omitted if the speaker has a predetermined position (for example, the speaker may be a center speaker 108a, 208a, 308a, 408a, 508a and shall only be used as a center speaker in front of a listener's position). The step may also be omitted if the microphone array 526 is used. By using the microphone array, the audio signal source device 500 may automatically determine the position of the first speaker by the different sound transit times received by the different microphones 526a of the microphone array 526. Therefore, as described above, a certain orientation of the microphone array 526 should be guaranteed, for example by using a marking 526b that shall be directed towards the center speaker 508a, for example.

In a fifth step, the controller 122, 222, 322, 422, 522 of the audio signal source device 100, 200, 300, 400, 500 identifies a network delay time plus a processing delay time plus an audio transit delay time for the first speaker by comparing the time of transmitting the digital audio calibration signal and recording the calibration sound signal. This network delay time plus the processing delay time plus the audio transit delay time may be referred to as a calibration delay in the following.

The steps described above may be repeated for each speaker of the audio system. For example, in the audio system shown in Fig. 1 , the above steps may be carried out five times and a calibration delay may be determined for every speaker. Further, in order to increase the accuracy, the steps may be carried out a plurality of times for each speaker and a mean calibration delay may be calculated. Further, calibration sound signals with different amplitudes and/or frequencies may be transmitted to the speakers in order to calculate a mean calibration delay. A frequency sweep might also calibrate the frequency response and/or the group delay of individual speakers. If the audio system includes a subwoofer the system might identify usual speakers and the subwoofer by performing a frequency sweep during the calibration process. In a sixth step, the audio signal source device 100, 200, 300, 400, 500 collects the individual calibration delays of all connected speakers (e.g., in the audio system of Fig. 1 , of the speakers 108a-108e).

In a seventh step, the audio signal source device 100, 200, 300, 400, 500 may calculate a predetermined delay for at least one or each one of the speakers. Hence, the predetermined delay may be determined by the audio signal source device 100, 200, 300, 400, 500. The predetermined delay is the delay that should be applied to the audio channel of a speaker in order to achieve a synchronized listening experience at the location of the microphone 126, 226, 326, 426 or the microphone array 526. Hence, if the individual predetermined delays are applied to each channel, two signals of the multichannel digital audio stream that are intended to be heard at the same time are received at the same time at the listener's position. The predetermined delay may be calculated from the respective calibration delays of the individual speakers. Hence, the predetermined delay may be determined based on a time difference between transmitting the digital audio calibration signal and receiving the calibration sound signal.

In an eighth step, in the audio systems shown in Figs. 1 , 3, and 5, the audio signal source device 100, 300, 500 may apply the individual predetermined delays to at least one or each one of the channels as shown in Fig. 6. Therefore a delay information may be stored in the memory 1 16, 316, 516. From the delay information, the predetermined delays for each channel (for each sound output device 106, 206, 306, 406, 506) can be derived.

Alternatively, in an eighth step, in the audio systems shown in Figs. 2 and 4, a delay information may be sent from the audio signal source device 200, 400 to the individual sound output devices 206, 406. Either the delay information comprises information on the predetermined delays for all sound output devices 206, 406 or one delay information is generated for each one of the sound output devices 206, 406 and transmitted to the individual sound output device 206, 406. In any case, the sound output device 206, 406 can derive the predetermined delay for its channel from the delay information sent to the sound output device 206, 406. The delay information may be stored in a memory 216, 416 of the sound output devices 206, 406. During audio playback, the individual predetermined delay may be applied to the digital audio stream as shown in Fig. 7 and as described above. In all the embodiments described in this application, the transmitter 120, 220, 320, 420, 520 may be used as a first transmitter for transmitting the digital audio stream, as a second transmitter for transmitting the digital audio calibration signal, and as a third transmitter for transmitting the delay information to the sound output devices 106, 206, 306, 406, 506. Alternatively, separate first, second, and third transmitters may be used that might use different communication paths.

Alternatively to the above-described embodiments, the speakers might not be part of a cinema surround-sound system, but might be speakers in a different room. This scenario is called "party-streaming" where all speakers in the home play-out the same audio signal. The same principles as described above can also be applied in this case. During the calibration process it may be determined which channel of the stream shall be decoded by each speaker. For example, two speakers may be provided in another room, and one of them plays the left stereo signal and the other one plays the right stereo signal.

If the used network is a PLC network using adaptive constellations, the digital audio stream might be multicast to all participating speakers. Such a multicast stream will not be received by any further nodes connected to the PLC network.

This means that the audio signal source device collects the channel status information of the communication channel to each sound output device and derives the tone maps of the OFMD carrier constellations. For each carrier the audio signal source device selects the maximum constellation that can be received and error free decoded by all sound output devices. The audio signal source device uses for the transmission of the digital audio stream to all sound output devices the common maximum tone map.

In a typical home cinema all speakers and the audio signal source device are located in the same room. All sockets in the room may be connected to the identical fuse. It is expected that the links to all devices participating to the audio network have a low attenuation compared to the link to other PLC devices also located in the home. This follows that the multicast stream might utilize higher constellations providing higher throughputs.

Alternatively the digital audio stream might be broadcasted to the complete home network using the most robust communication setup the network is capable of. In the case the home network is a Homeplug AV PLC network the ROBO mode might be used. Here more network resources may be allocated than if the multicast transmission is used. The digital audio stream might be a compressed stream requiring less data throughput rates than the sum of all individual audio streams. Further, a sound output device according to the present invention, including a home networking modem (receiver), a decoder, a processor, delay lines (delay unit), etc. may be realized using a DSP (digital signal processor). The decoding process may be done in software. This has the additional benefit that the system can easily be adapted by software update if new decoding formats or algorithms appear on the market. The invention described above plus the possibility to upgrade the software enables the user to add e.g., two more speakers to the audio system at a later time and to migrate e.g., from a Dolby™ 5.1 to a Dolby™ 7.1 surround sound system.

Thus, the above embodiments may also be described as follows.

Today's Surround Sound Systems consist of a central sound decoding unit where analog speakers are connected by individual speaker cables. Dolby™ 5.1 or 7.1 systems are very popular. Usually the women acceptance factor (WAF) is very low of these systems because of the multiple cables in the living room. When replacing the cables by a home network (WiFi or PLC) the speakers should be synchronized to guarantee a simultaneous audio play-out. Such synchronization may be expensive at a home network. Integrating a Surround Sound Decoder into each speaker and broadcasting the full multiple audio stream to all speakers over the home network avoids the expensive synchronization among the home network. In state of the art systems, the central decoding unit processes the decoding for all speakers. Analog cables connect the speakers in the room. The two front speakers might be chained after the Subwoofer.

There are systems with wireless rear speakers available, where a central unit is decoding the Surround Sound and a WiFi connection transports two audio streams bundled into one WiFi communication stream to a separate box (located at the rear side of the room) where two analog speakers are connected by analog audio cables.

When replacing the cables by a Home Network (WiFi or PLC) the speakers should be synchronized to guarantee a simultaneous audio play-out. Synchronization requirements are very hard for cost sensitive consumer electronic devices. The analog sound play-out of individual speakers should be synchronized to a precision of a few με (microseconds). If this precise synchronization is not guaranteed the analog play-out signals are affected by phase modulations. When a person listens to such signals affected by jitter, this results into the impression of moving speakers. Such precise synchronization may require expensive additional components doing time- stamping of packets, defining extra priorities in handling of the data packets, precise clocks at all network nodes, etc. These additional components may be expensive in a consumer electronic home network. In the embodiments, multiple Surround Sound decoders are embedded into a Surround Sound system. E.g. each speaker may be equipped with a Surround Sound decoder. The speakers may be active speakers with audio amplifiers included.

Figs. 1 and 2 show an audio signal source device (e.g., a Blu-ray Disc™ or DVD player, TV receiver, Internet Modem, etc.) forwarding the complete surround sound audio stream to all speakers. Each speaker may receive the complete surround sound audio stream, decodes it using the embedded surround sound decoder and renders the signal intended for this speaker. The signal forwarding might be done via any home network like WiFi or PLC. If data packet jitter (caused by e.g., delay, collisions or retransmissions) occurs on the home network to the broadcasted surround sound stream, all individual audio signals are affected simultaneously. This results in a common delay to all audio signals, but no individual impact on a single audio signal. If the data rate delivering the data to the speakers varies and a constant play-out rate must be guaranteed, a buffering of the play-out data might be implemented to guarantee the constant play-out in between the individual speakers, even if there is some delay in the stream from the audio source. Additionally, it might be to ensure that e.g., the video is synchronous to the audio. However, human listening impression is more tolerant against a constant delay of all speakers compared to individual delays between one speaker to other speakers.

The individual speakers may decode the surround sound stream at each location identically with a constant processing time of each decoding process.

Figs. 3 and 4 show combined solutions where some speakers have the surround sound decoder implemented and are directly connected to the home network. Other speakers are connected via analog cables to a decoder box, where the decoder box only is connected to the home network. To calibrate the Surround Sound system the microphone may be located in the middle of the room or at the favorite position where listener enjoys the home cinema experience. The microphone may be connected to the audio signal source device using an analog cable. The calibration process may measure the delays caused by the Home Network plus the delays and/or attenuation caused by the individual audio signal propagation from the speaker to the microphone. When the individual delays and/or attenuations of each speaker are known, the audio signal source may forward this information to the speakers. Each decoder embedded in the speaker may memorize his individual delay and respects it at the audio play-out.

Alternatively, the audio signal source might decode and re-encode the multiplexed surround- sound signal to take into account the individual delays and attenuations (some of the intelligence is moved from the speakers to the audio signal source). The calibration process also may identify which speaker is located where by playing signals only at individual speakers. User interaction may be used here to define the speaker. Which speaker e.g., is the rear left one or the center speaker? A frequency sweep might also calibrate the frequency response or/and the group delay to individual speakers. The calibration process might follow this sequence:

Audio Signal Source Device (ASSD, e.g. device 100, 200, 300, 400 or 500) initiates a sound on 1 st speaker in the Surround Sound Stream

• Stream is broadcasted over the Home Network to all speakers

• 1 st speaker plays the sound (all other speakers don't) and signal is recorded by the ASSD using the microphone

• User defines the location of the speaker at the setup menu of ASSD

• ASSD identifies the delay of the Home Network plus the audio transmission for 1 st speaker by comparing the initiated and recorded sound

• ... the steps described above are repeated for each speaker the ASSD is capable of. · ASSD collected the individual delays of all connected speakers

• ASSD calculates the delay each speaker shall set up to achieve a play-out where the center of the audio is at the location of the microphone

• ASSD forwards the information of the delay each speaker shall set up or alternatively decodes and re-encodes the multiplexed audio stream accordingly with its delay

· Each speaker applies the delay addressed to him to upcoming audio signals (this step may not be applied if the second alternative in the previous step is used) Fig. 1 shows the system where the individual delays of the speakers are inserted to the surround sound stream in the audio signal source device. For re-encoding the stream any proprietary data format might be used like AC3, Dolby™, etc. The stream where all sound signals are included may be broadcasted to the speakers.

The system might utilize multiple microphones, as depicted in Fig. 5. The multiple microphones might be an array of microphones where the distances and arrangement of the microphones are fixed and known to the system. The user may place the microphone array in a way that the orientation of the microphones (indicated e.g., with an arrow on the microphone array) spots to the center speaker or to the screen of the home cinema. If multiple microphones are used, the system may be able to identify the location of the speakers during the calibration process. This may make the involvement of the user to indicate the location of the speakers during the calibration process obsolete. If the Home Cinema system also includes a subwoofer (as shown in Figure 4c) the system might identify usual speakers and the subwoofer by performing a frequency sweep during the calibration process.

The speakers might not be part of a cinema surround-sound system, but might be speakers in another room. This scenario is called "party-streaming" where all speakers in the home play-out the same audio signal. The same principles as described above can also be applied in this case. During the calibration phase it has to be determined which of the streams has to be decoded by each speaker. E.g. there are two speakers in another room, where one of them plays the left stereo signal and the other plays the right stereo signal.

If the Home Network is e.g., a PLC network using adaptive constellations, the Surround Sound Stream might be multicast to all participating speakers. Such a multicast stream will not be received by any further nodes connected to the PLC network.

This means:

· the ASSD collects the channel status information of the communication channel to each speaker and derives the tone maps of the OFDM carrier constellations

• for each carrier the ASSD selects the maximum constellation that can be received and error free decoded by all speakers

• ASSD uses for the transmission of the Surround Sound Signal to all speakers the common maximum tone map In a typical home cinema all speakers and the ASSD are located in the same room. All power outlets in the room are connected to the identical fuse. It is expected that the links to all devices participating to the home cinema application have a low attenuation compared to the link to other PLC devices also located in the home. This follows that the multicast stream might utilize higher constellations providing higher throughputs.

Alternatively the Surround Sound Stream might be broadcasted to the complete home network using the most robust communication setup the network is capable of. In the case the home network is a Homeplug AV PLC network the ROBO mode might be used. Here more network resources are allocated than if the multicast transmission is used.

The Surround Sound Signal might be a compressed stream requiring less data throughput rates than the sum of all individual audio streams. Fig. 2 shows a block schematic of a plurality of speaker boxes. The PLC modem receives the stream send by the ASSD via the home network.

There may be more information sent from the ASSD to the speaker box like

• adjusting the audio volume,

· selecting the audio channel,

• defining the delay for this speaker,

• control information to the sound decoder,

which are handled by the processor. The Surround Sound Decoder might derive audio volume information out of the received data stream. This information might also set the level of the amplifier. The Surround Sound Signal is decoded, the corresponding audio stream selected, delayed as evaluated during the calibration process, Digital to Analog converted, amplified and rendered by the speaker. When the broadcasted data packets arrive at a speaker box at time = t(in) the box may use this time stamp to sync the play-out. Maybe the oscillators in all speakers do not run exactly at the same frequency, because cheap components are used which may be not identical.

During a long play-out session (e.g., a 90 min movie) the processing in the individual speakers might scatter. Due to the data packets are broadcasted a packet should arrive at the same time t(in) at all speakers. This time t(in) might be used to synchronize the play-out time at the analog speaker. Systems like a speaker including home networking modem, decoder, processor, delay lines, etc may be realized using a DSP (Digital Signal Processor). The decoding process may be done in software. This has the additional benefit, that the system can easily be adapted by software update if new decoding formats or algorithms appear on the market.

The idea described above plus the possibility to upgrade the software enables the user to add e.g., two more speakers to his system at a later time and migrate e.g., from a Dolby™ 5.1 to a Dolby™ 7.1 surround sound system.