Field

The present disclosure relates to transmitter devices, receiver devices and systems.

Background

Wireless connections, such as Wi-Fi™ and Bluetooth™, can be used to transfer audio and data between transmitter and receiver devices. Wired connections can transfer audio and data more reliably than wireless connections. Flowever, wired connections can still be susceptible to noise and interference. Considerations around integrity, in particular audio integrity, also therefore apply to wired connections. This may be particularly relevant when audio and data are being communicated together, for example as data-over-audio.

US 5,612,943 A describes a system for carrying transparent digital data within an audio signal. A signal processing system comprises inputs for an analogue audio signal and a digital data signal. The digital data signal is modulated to an analogue data signal in an inaudible frequency band. The analogue data signal has carrier frequencies substantially between 18 kilohertz (kHz) and 20kFlz, such as 18.5kFlz and 19.5kFlz. Filters are used to ensure that the audio signal is restricted to audible frequencies, substantially below 18kHz, and that the analogue data signal is restricted to inaudible frequencies, substantially between 18kHz and 20kFlz. The two analogue signals are then combined into a composite analogue signal. The composite signal is stored on a medium such as a compact disc. Filters are used to extract and separate the two analogue signals from the composite signal stored on the medium. The analogue data signal is demodulated to retrieve the original digital data signal.

US 8,781,147 B1 describes an acoustic headphone having a single interface to receive audio signals and configuration data. An interface between a programming system and a set of headphones allows the transmission of both audio and digital data over analogue audio signal lines of the headphones. Circuitry on the programming system is configured to transmit digital data over the analogue audio signal lines by either modulating a carrier frequency with the digital data such that the digital data is transmitted over non-audible frequencies or by time-multiplexing the transmission of digital data and analogue audio data. The audio signal ranges in frequency from 20 Flertz (Hz) to 20kFlz. The modulated digital data has a frequency that is higher than the audible frequency limit, i.e. is above 20kFlz. Circuitry on the headphones is configured to receive digital data by demodulating the modulated digital data or by de-multiplexing the time-multiplexed digital and analogue audio data.

Summary

According to first embodiments, there is provided a transmitter device comprising: a single-ended to differential converter configured to convert a single-ended analogue audio input signal into a differential pair of analogue audio input signals, the differential pair of analogue audio input signals comprising an in-phase analogue audio input signal and an anti-phase analogue audio input signal; a differential amplifier configured to: receive the in-phase and anti-phase analogue audio input signals from the single-ended to differential converter; receive a common-mode voltage data signal; generate a first analogue audio output signal of a differential pair of analogue audio output signals by modulating the common-mode voltage data signal onto the in-phase analogue audio input signal; and generate a second analogue audio output signal of the differential pair of analogue audio output signals by modulating the common-mode voltage data signal onto the anti-phase analogue audio input signal; and an interface configured to output the differential pair of analogue audio output signals to a receiver device along a differential cable, wherein the common-mode voltage data signal has a frequency of less than 20 Hertz. According to second embodiments, there is provided a receiver device comprising: an interface configured to receive a differential pair of analogue audio signals from a transmitter device along a differential cable; and one or more components configured to be used to derive: a common-mode voltage data signal using the differential pair of analogue audio signals; and a single-ended analogue audio signal based on the differential pair of analogue audio signals, wherein the common-mode voltage data signal has a frequency of less than 20 Hertz. According to third embodiments, there is provided a system comprising: a transmitter device according to the first embodiments; and a receiver device according to the second embodiments.

Further embodiments described herein provide methods and computer-readable instructions to cause, when executed, some or all of such methods to be performed.

Brief Description of the Drawings

Various embodiments will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 shows a schematic representation of an example of a system in accordance with embodiments;

Figure 2 shows a schematic representation of an example of a transmitter device in accordance with embodiments;

Figure 3 shows a graph depicting a representation of common-mode voltage data frequency in accordance with embodiments;

Figure 4 shows a schematic representation of an example of a receiver device in accordance with embodiments;

Figure 5 shows a graph depicting a sine wave and a corresponding graph depicting harmonics of the sine wave;

Figure 6 shows a graph depicting a square wave and a corresponding graph depicting harmonics of the square wave;

Figure 7 shows a graph depicting a triangle wave and a corresponding graph depicting harmonics of the triangle wave;

Figure 8 shows a schematic representation of another example of a system in accordance with embodiments;

Figure 9 shows a schematic representation of another example of a receiver device in accordance with embodiments;

Figure 10 shows a schematic representation of another example of a transmitter device in accordance with embodiments; and

Figure 11 shows a schematic representation of another example of a system in accordance with embodiments.

Detailed Description Like features are shown in different drawings using the same reference numeral but incremented by a multiple of 100.

In general terms, examples described herein provide transmitter devices, receiver devices and systems configured to communicate data-over-audio. Such communication may involve transmitting and/or receiving data-over-audio. In examples, data can be modulated onto analogue audio and communicated along a differential cable (also known as a "balanced cable") with no, or limited, adverse audible effect to the audio, thereby preserving audio integrity. The modulated data may be digital data. The modulated data may comprise peripheral configuration data, which can be used to configure peripheral devices. Such communication may occur while audio is playing in real-time (in other words, "live"). The differential cable may be a shielded cable, such as an XLR cable.

As will be explained in more detail below, the data may be applied to the analogue audio by modulating a common-mode voltage of a differential pair of audio signals. In examples, the data frequency is sub-20Hz, which is outside the 20Hz-20kHz audio band and, specifically, is below the lower limit of this frequency range. This can avoid affecting, at least significantly, the audio band of 20Hz-20kHz. Although frequencies above 20kHz are also outside the 20Hz-20kHz audio band, it has been identified that use of such higher frequencies can affect audio integrity when data is modulated onto the common-mode voltage. As such, although both frequencies below 20Hz and above 20kHz are outside the 20Hz-20kHz audio band, examples described herein use the lower frequencies. This differs from some known systems which transfer data using higher frequencies. The transmitted common-mode voltage waveform may be shaped such that it does not contain high-frequency harmonics, or at least contains reduced high-frequency harmonics compared to an unshaped waveform. For example, the transmitted common-mode voltage waveform may be shaped to be a triangular wave. This, again, can maintain audio integrity. The low-rate, sub-20Hz data can, however, be used to trigger the system to switch to a high-rate data mode. This may involve temporarily disabling audio to send data at a higher rate, namely at 20Hz or above. In examples, the transmitter device does not require the receiver device to have circuitry to derive the data from the analogue audio for the transmitter device and the receiver device to operate exclusively in an audio transfer mode (in other words, with no data transfer), and vice versa.

Referring now to Figure 1, there is shown an example of a system 100. The example system 100 comprises a transmitter device 102, a receiver device 104, and a differential cable 106 coupled to the transmitter and receiver devices 102, 104. Although only a single transmitter device 102, receiver device 104, and differential cable 106 are shown in Figure 1, the system 100 may comprise multiple transmitter devices 102, receiver devices 104, and/or differential cables 106.

The system 100 may comprise a public address (PA) system. The PA system may be for a live venue, where the transmitter device 102 corresponds to a main mixing desk and the receiver device(s) 104 correspond(s) to peripheral speakers. In such a system 100, the mixing desk can have control over the peripheral speakers using the data-over-audio technology described herein.

The example system 100 can therefore allow for data transfer between two devices, namely the transmitter and receiver devices 102, 104, via an existing, wired connection, namely the differential cable 106.

As explained above, the differential cable 106 may be an XLR cable, which is a cable with XLR connectors as its ends. An XLR cable comprises three wires, which may be known as "Hot", "Cold", and "Shield". The Hot and Cold wires are a differential, twisted pair, resistant to common-mode noise (also known as "common-mode interference"). This allows for much longer cable runs than would otherwise be possible. The shielding also helps suppress noise.

Transferring data using a wired connection can, in accordance with example, use existing cabling that is already in place by the very nature of example setups described herein. This reduces or removes the need for additional system setup. This also provides a physical connection to one or more peripheral devices, which reduces the inherent risk of losing connection with wireless technology.

To transfer data in the system 100, for example from the transmitter device 102 to the receiver device 104, the Hot and Cold wires of the differential cable 106 may be physically switched from an audio-and-data line to a data-only line to allow data transfer to occur independently of the audio. The data transfer may, in such cases, use a data rate of at least 20Hz and, in particular, significantly higher data rates than 20Hz. However, this may involve both the transmitter side and the receiver side being instructed to switch from the audio-and- data transfer mode to the data-only transfer mode, and back. In some examples described herein, data is modulated onto an analogue audio signal and data transfer can be initiated from only the transmitter side.

Referring to Figure 2, there is shown an example of a transmitter device 202. The example transmitter device 202 comprises a component 208, in this example a single-ended to differential converter, configured to convert a single-ended analogue audio input signal 210 into a differential pair of analogue audio input signals 212, 214. The differential pair of analogue audio input signals 212, 214 comprises an in-phase analogue audio input signal 212 (which may also be known as a "positive analogue audio input signal") and an anti-phase analogue audio input signal 214 (which may also be known as a "negative analogue audio input signal").

The example transmitter device 202 also comprises a component 216, in this example a differential amplifier 216, configured to receive the in-phase and anti-phase analogue audio input signals 212, 214 from the single-ended to differential converter 208. The differential amplifier 216 is also configured to receive a common-mode voltage data signal 218. The differential amplifier 216 is configured to generate first and second analogue audio output signals 220, 222 of a differential pair of analogue audio output signals 220, 222 by modulating the common-mode voltage data signal 218 onto the in-phase and anti-phase analogue audio input signals 212, 214 respectively.

The example transmitter device 202 also comprises a component 224, in this example an interface 224, configured to output the differential pair of analogue audio output signals 220, 222 to the receiver device 104 along the differential cable 106. The interface 224 may correspond to an XLR connector and the differential pair of analogue audio output signals 220, 222 may be output via Hot and Cold wires of an XLR cable 106.

As will be explained in more detail below, the example transmitter device 202 is operable to output the differential pair of analogue audio output signals 220, 222 while the receiver device 104 is playing, in real-time, the audio from the differential pair of analogue audio output from signals 220, 222. In particular, the system 100 is configured such that the receiver device 104 does not need to stop playing audio for the example transmitter device 202 to output the differential pair of analogue audio output signals 220, 222 with the modulated common-mode voltage data signal 218.

It should be understood that Figure 2, and other Figures described in more detail below, show, schematically, a low audio-signal-to-common-mode-voltage ratio to facilitate understanding and demonstration of the above-described modulation of the common-mode voltage data signal 218 onto the in-phase and anti-phase analogue audio input signals 212, 214 respectively. However, as will be explained in more detail below, examples described herein actually provide measures to increase the audio-signal-to-common-mode-voltage ratio.

Referring to Figure 3, there is shown an example graph.

The common-mode voltage of the differential pair of wires of the differential cable 106 is the voltage common to both of the wires. In theory, the common-mode voltage can be modulated without affecting analogue audio on those wires. This is because the purpose of using a differential pair of wires is to eliminate common-mode voltages (in other words, noise) at the receiving end. However, in practice, a parameter known as "Common-Mode Rejection Ratio" (CMRR) determines how much of the common-mode voltage is removed (in other words, rejected). CMRR decreases as frequency increases, primarily owing to parasitic capacitance of Printed Circuit Board (PCB) layouts, cables, Integrated Circuits (ICs) and so on. This means that the higher the frequency of the CMRR modulation, the more the CMRR will negatively affect the analogue audio at the receiver side. Modulating data at low frequencies therefore maintains the integrity of the audio signal, albeit with a trade-off of a lower data rate. In examples, the data rate is limited to be less than 20Hz while audio is also being conveyed, such that the data is outside and, in particular, below the 20Hz-20kHz audio band. While data could, in principle, be transmitted at 20Hz or above while audio is also being conveyed, the integrity of the audio would be reduced. This applies if the data were transmitted at a rate of 20Hz-20kHz. This applies even more if the data were transmitted at a rate above 20kHz because of the above-mentioned decrease in CMRR, primarily owing to parasitic capacitance.

Referring again to Figure 3, in accordance with examples described herein, the common-mode voltage data signal 318 has a frequency of less than 20Hz.

The transmitter device 102, 202 may be operable in a low-rate date mode in which the transmitter device 102, 202 conveys information to the receiver device 104 using a common-mode voltage data signal 318 having a frequency of less than 20Hz.

The transmitter device 102, 202 may also be operable in a high-rate data mode in which the transmitter device 102, 202 conveys information to the receiver device 104 by outputting data having a frequency of at least 20Hz to the receiver device 102 along the differential cable 106. This may involve the differential wires being physically switched to a data-only line to allow high-rate data transfer to occur independently of audio. The transmitter device 102, 202 may be operable to include, in the common-mode voltage data signal 318, data indicative of the transmitter device 102, 202 switching to the high-rate data mode.

The transmitter device 102, 202 may be operable to include, in the data having the frequency of at least 20 Hz, data indicative of the transmitter device 102, 202 switching from the high-rate data mode to the low-rate data mode.

As such, the high-rate data mode can be provided by implementing the physical wire switching described above. The low-rate data mode can be used to trigger the high-rate data mode on both the transmitter device 102, 202 and the receiver device 104. The high-rate data mode allows for larger data transfers. Such data transfers may be for software updates, for example. Audio transfer and/or audio playback may be disabled during the high-rate data mode.

Referring to Figure 4, there is shown an example of a receiver device 404.

The example receiver device 404 comprises a component 426, in this example an interface, configured to receive a differential pair of analogue audio signals 428, 430 from the transmitter device 102, 202 along the differential cable 106. The differential pair of analogue audio signals 428, 430 received by the receiver device 404 corresponds to the differential pair of analogue audio output signals 220, 222 output by the transmitter device 102, 202 along the differential cable 106. The interface 246 may correspond to an XLR connector and the differential pair of analogue audio signals 428, 430 may be received via Hot and Cold wires of an XLR cable 106.

The example receiver device 404 comprises one or more components 432, 434, 436 configured to be used to derive a common-mode voltage data signal 438 and an amplified differential pair of analogue audio signals 440, 442 using the differential pair of analogue audio signals 428, 430. In examples, such deriving involves demodulating the differential pair of analogue audio signals 428, 430. The derived common-mode voltage data signal 438 corresponds to the common-mode voltage data signal 218, 318 used by the transmitter device 102, 202. The amplified differential pair of analogue audio signals 440, 442 corresponds to the differential pair of analogue audio signals 428, 430, but amplified based on the gain of the components 432, 434, 436. The common-mode voltage at point 444 is equal to the voltage which is common (mode) to both of the amplified differential pair of analogue audio signals 440, 442. Point 444, in effect, exposes the common mode voltage in the amplified differential pair of analogue audio signals 440, 442. This is because the audio parts of the amplified differential pair of analogue audio signals 440, 442 are exactly opposite to each other and cancel out. In this example, the derived common-mode voltage data signal 438 has a frequency of less than 20Hz.

The example receiver device 404 also comprises a component 446, in this example a differential line receiver, configured to combine the amplified differential pair of analogue audio signals 440, 442 into a single-ended analogue audio signal 448. As such, the single- ended analogue audio signal 448 is derived by the component 446 using the amplified differential pair of analogue audio signals 440, 442, which is based on the differential pair of analogue audio signals 428, 430. In particular, the component 446 derives the single-ended analogue audio signal 448 as the difference between the amplified differential pair of analogue audio signals 440, 442, rejecting the common mode voltage in the amplified differential pair of analogue audio signals 440, 442. The single-ended analogue audio signal 448 corresponds to the single-ended analogue audio input signal 210. The single-ended analogue audio signal 448 may be played by the receiver device 404.

As such, the example receiver device 404, in effect, splits the differential pair of analogue audio signals 428, 430 into the common-mode voltage data signal 438 and the single-ended analogue audio signal 448. The derived common-mode voltage data signal 438, in effect, has audio removed and the single-ended analogue audio signal 448, in effect, has the data signal removed.

In this example, the receiver device 404 is operable to derive the common-mode voltage data signal 438 and the single-ended analogue audio signal 448 while the receiver device 404 is playing, in real-time, the audio received from the transmitter device 102, 202.

In this example, the differential audio signals only have the common-mode voltage data signal 438 removed after they pass through the component 446. The component 446 only amplifies the differences between the signals 440 and 442 and rejects anything that is common (mode). The receive point 444 of the common-mode voltage data signal 438 is the point in the circuit where the audio parts of the two differential signals 440, 442 combine to cancel each other out (as they are opposite), whereas the common mode does not cancel out. In this specific example, the common mode is presented at unity gain.

Reference is now made to Figures 5 to 7. Figure 5 shows a set of corresponding graphs showing an example sine wave having no higher-order harmonics. Figure 6 shows a set of corresponding graphs showing an example square wave having higher-order harmonics. Figure 7 shows a set of corresponding graphs showing an example triangle wave having reduced higher-order harmonics compared to those of the square wave shown in Figure 6.

Traditionally, data signals are square waves having values of "0" or "1", such as is shown in Figure 6. Flowever, as also shown in Figure 6, they have high-frequency harmonics from the sharp edge. A square wave modulated onto an analogue audio signal is relatively likely to be heard at the receiver end in view of the high-frequency harmonics. As shown in Figure 7, a triangle wave has far fewer high-frequency harmonics than a square wave and, therefore, is less likely to be audible at the receiver end if modulated onto an analogue audio signal. As will be explained in more detail below, examples shape a square wave input data signal to be a triangle wave, or at least to have fewer high-frequency harmonics.

Referring to Figure 8, there is shown another example system 800.

In the example system 800, a single-ended to differential converter 808 of a transmitter device 802 receives a single-ended analogue audio input signal 810 (labelled "Audiojn" in Figure 8) and outputs a differential pair of analogue audio input signals 812, 814 (labelled "Audio_ln_±" in Figure 8), comprising in-phase and anti-phase analogue audio input signals 812, 814 (labelled "Audio_ln_+" and "Audio_ln_-" respectively in Figure 8), to a differential amplifier 816.

The example system 800 also comprises a component 850, which in this example is a low-pass filter 850. The low-pass filter 850 is configured to receive a signal 852 (referred to hereinafter as the "low-pass filter input data signal") having higher-order harmonics of the frequency (of less than 20Flz) of the common-mode voltage data signal 818. In this example, the low-pass filter input data signal 852 is a square wave. The low-pass filter 850 is configured to output a signal 854, which is referred to hereinafter as the "low-pass filter output data signal". The low-pass filter output data signal 854 has reduced (for example, fewer) higher- order harmonics than the low-pass filter input data signal 852. In this example, the low-pass filter output data signal 854 is a triangle wave. The common-mode voltage data signal 818 is based at least on the low-pass filter output data signal 854. As such, and with reference again to Figures 6 and 7, the low-pass filter 850 may therefore remove the sharp edge of the square- wave low-pass filter input data signal 852 to provide a triangle-wave low-pass filter output data signal 854. The example transmitter device 802 comprises a component 856, which in this example is a voltage reduction component 856. In this specific example, the voltage reduction component 856 is a voltage divider. The voltage reduction component 856 is configured to receive a signal 858 (referred to hereinafter as the "voltage reduction component input data signal") having a given voltage level. In this example, the voltage reduction component input data signal 858 is the low-pass filter output data signal 854 output by the low-pass filter 850. In this example, the voltage reduction component 856 is configured to output a signal 860 (referred to hereinafter as the "voltage reduction component output data signal") having a reduced voltage level compared to the voltage reduction component input data signal 856. In this example, the voltage reduction component output data signal 860 is a triangle wave. The common-mode voltage data signal 818 is based at least on the voltage reduction component output data signal 860. In this example, the common-mode voltage data signal 818 is the voltage reduction component output data signal 860. As such, in this example, the common-mode voltage data signal 218, 318, 818 is a triangle wave.

The voltage reduction component 856 enables the common-mode voltage swing, namely the variation in the common-mode voltage, to be reduced relative to the audio signal voltage such that the common-mode voltage is much smaller than the audio signal voltage. In other words, the audio-signal-to-common-mode-voltage ratio is increased. This reduces the likelihood of the data being heard over the audio.

In the example system 800, the differential amplifier 816 receives the in-phase and anti-phase analogue audio input signals 812, 814 from the single-ended to differential converter 808 and receives the common-mode voltage data signal 818 from the voltage reduction component 856. The differential amplifier 816 then modulates the common-mode voltage data signal 818 onto the in-phase and anti-phase analogue audio input signals 812, 814, and outputs the differential pair of analogue audio output signals 820, 822 (labelled "Signal_Out_±" in Figure 8) via the interface 824. In this specific example, the differential pair of analogue audio output signals 820, 822 comprises first and second analogue audio output signals 820, 822 (labelled "Signal_Out_+" and "Signal_Out_-" respectively in Figure 8). In this specific example, the interface 824 comprises an XLR (male) connector.

The receiver device 804 of the example system 800 comprises componentry 832, 834 that receives a differential pair of analogue audio signals 828, 830 (labelled "Signal_ln_±" in Figure 8) from the interface 826. The differential pair of analogue audio signals 828, 830 correspond to the differential pair of analogue audio output signals 820, 822. In this example, the componentry 832, 834 comprises an instrumentation amplifier. The instrumentation amplifier 832, 834 derives an amplified differential pair of analogue audio signals 840, 842 (labelled "lnst_Amp_±" in Figure 8) using the differential pair of analogue audio signals 828, 830. A differential line receiver 844 receives the amplified differential pair of analogue audio signals 840, 842 from the instrumentation amplifier 832, 834 and combines them to output a single-ended analogue audio signal 848 (labelled "Audio_Out" in Figure 8). The receiver device 804 may then play audio based on the single-ended analogue audio signal 848. In this specific example, the interface 826 comprises an XLR (female) connector. In this specific example, the differential pair of analogue audio signals 828, 830 comprises first and second analogue audio signals 828, 830 (labelled "Signal_ln_+" and "Signal_ln_-" respectively in Figure 8).

The instrumentation amplifier 832, 834 also derives a common-mode voltage data signal 838 using the differential pair of analogue audio signals 828, 830. A component 862, in this example a Schmitt Trigger, of the receiver device 804 receives the derived common-mode voltage data signal 838 (labelled "VcmRX_a" in Figure 8) from the instrumentation amplifier 832, 834 and re-clocks the common-mode voltage data signal 838 to a square wave 864 (labelled "VcmRX" in Figure 8) at a particular voltage level (also known as "logic level").

As explained above, the common-mode voltage data signal 818 may be based at least on the low-pass filter output data signal 854 and may be based at least on the voltage reduction component output data signal 860. In this example in which the example system 100 comprises both the low-pass filter 850 and the voltage reduction component 856, the common-mode voltage data signal 818 is based on both the low-pass filter output data signal 854 and the voltage reduction component output data signal 860. Flowever, in other examples, the common-mode voltage data signal 818 may be based on only one, or neither, of these signals 854, 860, for example where the system 800 comprises one but not the other, or neither, of the low-pass filter 850 and the voltage reduction component 856.

Examples described above provide one-way communication of a data signal from a transmitter device 102, 202, 802 to a receiver device 104, 404, 804 using data-over-audio technology as described herein. Examples that will now be described provide for two-way (also referred to herein as "bi-directional") data communication. Referring to Figure 9, there is shown another example of a receiver device 904. In this example, the receiver device 904 is operable, via components 966, to output a common mode voltage data signal 968 to the transmitter device 102, 202, 802 along the differential cable 106. In this example, the components 966 comprise two resistors configured to provide a direct current (DC) reference voltage (common-mode voltage) for the differential analogue audio signals 928, 930.

It should be understood that the receiver device 904 can output the common-mode voltage data signal 968 along the differential cable 106 even if the transmitter device 102, 202, 802 is communicating analogue audio to the receiver device 904 over the differential cable 106 at the same time. In such cases, the DC voltages on each the differential wires of the differential cable 106 will increase by the common-mode voltage. The receiver device 904 can still derive the audio from the differential analogue audio signals 928, 930 and, in effect, ignore the common-mode voltage data signal 938 that could also be derived.

Referring to Figure 10, there is shown another example of a transmitter device 1002.

The example transmitter device 1002 is operable to derive the common-mode voltage of the differential cable 106 using components 1070, 1072, 1074 to obtain a common-mode voltage data signal 1076. The common-mode voltage data signal 1076 obtained by the transmitter device 1002 corresponds to the common-mode voltage data signal 968 sent by the receiver device 104, 404, 804, 904. In particular, as explained above, the transmitter device 1002 can derive the common-mode voltage data signal 1076 even if the transmitter device 1002 is transferring analogue audio to the receiver device 104, 404, 804, 904 at the same time.

In this example, a single element comprising both single-ended to differential converter and differential amplifier functionality is shown using reference numerals 1008 and 1016.

In some examples, the derived common-mode voltage represents data (in particular, the common-mode voltage data signal 1076) having a frequency of less than 20Flz. In some examples, the transmitter device 1002 is operable to derive the common-mode voltage while outputting differential analogue audio output signals to the receiver device 104, 404, 804, 904 along the differential cable 106. In some examples, the derived common-mode voltage represents peripheral status data. In some examples, the transmitter device 1002 with bi-directional data communication functionality is configured to signal to the receiver device 904 with bi directional data communication functionality that it is switching into a listening mode such that, rather than communicating data to the receiver device 904, it will listen for data from the receiver device 904. The transmitter device 1002 may stay in the listening mode for a predetermined amount of time before reverting to a data transmitter mode, the receiver device 904 may signal once it has completed its data transfer to trigger the transmitter device 1002 to revert to the data transmitter mode, or otherwise. In other examples, the transmitter and receiver devices 1002, 904 with the bi-directional data communication functionality may switch intermittently between transmitting and listening in accordance with a predetermined switching pattern.

Referring to Figure 11, there is shown another example system 1100.

In this example, the system 1100 is a PA system for a live venue and comprises a main mixing desk 1102 connected to a series of 'N' peripheral speakers 1104 via a set of XLR cables 1106. In this specific example, some of the peripheral speakers 1104 are in a daisy-chain arrangement. In this specific example, others of the peripheral speakers 1104 have respective one-to-one connections with the mixing desk 1102 with no direct interconnectivity between each such peripheral speaker 1104. Such a in which mixing desk 1102 connects directly to each external peripheral speaker 1104, for example, using respective XLR cables, uses multiple outputs on the mixing desk 1102. Other arrangements are possible, such as one using only one-to-one connections, only daisy-chain connections, or otherwise.

The example system 1100 can be used to for live setup-configuration and A/B listening using the using the data-over-audio technology described herein. The mixing desk 1102 may communicate various different types of data to the peripheral speakers 1104. Such data may be configured to instruct the peripheral speakers 1104 to change a parameter that affects the audio, or to switch an internal feature, function and/or light on or off, for example.

Each peripheral speaker 1104 may comprise a digital signal processor (DSP). Each DSP may be configured to, amongst other things, monitor the status of its respective peripheral speaker 1104 and report peripheral status data to the main mixing desk 1102 based on the monitored status. Such reporting may be via one or more intermediate peripheral speakers 1104, between the reporting peripheral speaker 1104 and the main mixing desk 1102. The peripheral status data may comprise heartbeat data, via which a peripheral speaker 1104 can indicate that it is functioning correctly. The peripheral status data may comprise a warning about thermal shutdowns or one or more other errors. This adds reliability to the example system 1100. Other types of peripheral status data may be used. Additionally or alternatively, the peripheral speakers 1104 may report other types of data. For example, the peripheral speakers 1104 may report sonic quality or output.

As explained above, wireless technology can be unreliable generally, and more so in the context of a music venue when potentially thousands of people are in a room. People themselves impact wireless signals reception, especially at Wi-Fi™ and Bluetooth™ frequencies. In addition, large numbers of mobile telephones in such music venues also impact reliability. The data-over-audio technology described herein can use existing cabling for reliable communications and also such that no extra cabling is used, which in turn reduces setup overheads, such as time and cost.

Live venues generally have long runs of cable, which have a significant capacitance. This limits the speed of data they could carry, likely to within the audio band. Even if that data was run along separate cables, they would be parallel to the audio cables, and inevitably cause crosstalk or interference owing to the capacitive coupling of long runs of cable. This also effectively doubles amount of cable used. Examples described herein use existing, industry-standard cable interconnects and, therefore, do not require outlay for replacement.

Using the data-over-audio technology described herein in the example system 1100, a sound technician can sound check while audio is playing, as opposed to pausing the audio, adjusting the settings, and then playing the audio again. Such live A/B testing is especially effective in the context of a live PA system.

Another example of a system in which the data-over-audio technology described herein may be applied is a pedalboard system. In such a system, effects pedals on a pedalboard may be controlled via a single footswitch controller via existing audio connections. This can provide a powerful tool for pre-set control.

Features described above in relation to one example may be combined with features described above in relation to another example.

In addition, in examples described above, the common-mode voltage data signal 218, 318, 438, 818, 838, 858, 938, 968, 1018, 1076 has a frequency of less than 20Flz. In other examples, the common-mode voltage data signal 218, 318, 438, 818, 838, 858, 938, 968, 1018, 1076 has a higher maximum frequency. The maximum frequency may be in the audio band. For example, the higher maximum frequency may be 50Hz or 70Hz. The higher maximum frequency allows for a higher data rate. In addition, the extent to which such data would be audible depends, at least in part, on characteristics of the receiver device 104, 404, 804, 904, 1104. For example, using a 50Flz or 70Flz data rate may not reduce audible audio integrity where certain types of loudspeaker are used. As such, a higher data rate may be used without reduced audible audio integrity in such examples. Flowever, examples in which the common-mode voltage data signal 218, 318, 438, 818, 838, 858, 938, 968, 1018, 1076 has a frequency of less than 20Flz enable audible audio integrity to be maintained irrespective of the type of loudspeaker used, for example. Various measures (for example transmitter devices, receiver devices and systems) are therefore provided herein in which data having a frequency of at most 70Flz is modulated onto analogue audio signals and is transmitted over a balanced cable from a transmitter device to a receiver device. In some examples, the data has a frequency of at most 50Flz and, in some, specific examples has a frequency of less than 20Hz.

In examples described above, the input data signal has two logical values, corresponding to "0" or "1". In other examples, the input data signal may have more than two logical values, such as four logical values representing "00", "01", "10" and "11". Twice as much information could be conveyed in such examples, doubling the effective bit rate. Flowever, this may involve increasing the common-mode voltage swing such that additional logical values can readily be detected. This, in turn, reduces the audio-signal-to- common- mode-voltage ratio, which could introduce additional audible artefacts. The common-mode voltage swing could be maintained to mitigate this, though with an increased risk of errors in common-mode voltage data signal recovery.

In examples described above, the balanced cable 106, 1106 is an XLR cable, having XLR connectors at its ends. Other types of balanced cables may be used, an example of which is a balanced cable with TRS connectors at its ends, for example depending on the nature of the interfaces 224, 426, 824, 826.

In addition to measures (for example transmitter devices, receiver devices and systems) described in detail above, additional measures such as methods and computer- readable instructions to cause, when executed, some or all of such methods to be performed, are also provided by the present disclosure. One such example method comprises: generating a differential pair of analogue audio output signals by modulating a common-mode voltage data signal onto in-phase and anti-phase analogue audio input signals of a differential pair of analogue audio input signals; and outputting the differential pair of analogue audio output signals along a differential cable, wherein the common-mode voltage data signal has a frequency of less than 20Hz.