A BACKGROUND NOISE GENERATOR

A noise generator

The present invention relates to methods and apparatus for obscuring sound and particularly to noise generators and methods of making noise for simulating an acoustic scene and sound masking applications.

In addition to the voice of a user, electronic communication devices such as, for example, landline telephones and mobile telephones, transmit the signal of the background noise. This is often undesirable as the user may be disclosing confidential information by way of transmitting the background noise, such as, for example, in the case of call centres other background conversations.

Sound masking is a technique whereby an acoustic noise is deliberately introduced to obscure or mask unwanted sound. This may be desirable so as to reduce the distracting potential of certain sounds or to reduce the intelligibility of sound.

Sound masking systems having an electronic noise source, an amplifier and a loudspeaker, are commercially available. Such systems generate noise by filtering white noise signals using a shaping filter. The shaping filter modifies the white noise into a sound capable of adequately masking the components of the unwanted sound. A filter is also used to shape the masking noise such that it is more tolerable for the human ear as a background noise. The resulting masking noise may, for example, be described as a woosh, rush or hiss.

It is also desirable to create a virtual acoustic background, using a generated noise, which conveys a predetermined acoustic scene that a user may wish to portray, such as, for example, a user of a telephone may wish to convey a particular acoustic scene to whomever they are communicating with.

It is an object of the present invention to provide apparatus and a method for making an improved and more acceptable masking noise.

It is also an object of the present invention to provide apparatus and a method for making a virtual acoustic background.

According to the present invention there is provided a noise generator comprising signal processing means operable to receive one or more signals and process the one or more signals to generate a virtual acoustic background which simulates a predetermined acoustic scene and carries no discernable information content.

Also according to the present invention there is provided a method of generating a noise for simulating a predetermined acoustic scene, comprising the steps of providing signal processing means for receiving one or more sound signals, receiving at least one sound signal, and adapting the at least one sound signal to generate a virtual acoustic background of a predetermined acoustic scene and having no useful information content.

Also according to the present there is provided a communications system comprising a noise generator or a method for generating a noise, as described in the two preceding paragraphs, respectively.

Also according to the present invention there is provided an electrical or electromagnetic signal representing program codes for causing a noise generator to perform steps comprising: selecting at least one sound signal, from a plurality of sound signals, and adapting said selected one or more sound signals to generate a virtual acoustic background, which simulates a predetermined acoustic scene and carries no discernable information content.

Also according to the present invention there is provided a data carrier carrying a record of a signal as described in the preceding paragraph.

One or more sound signals may be received from a live source. The live source may be disposed within the environment in which the signal processing means is disposed or, alternatively, may be remote from the environment in which the signal processing means is disposed.

The noise generator may additionally comprise storage means for storing one or more recorded sound signals. The sound signals received by the signal processing means may be one or more of the recorded sound signals.

The storage means may be disposed proximate to the signal processing means. Alternatively, the storage means may be disposed remote from the signal processing means.

The noise generator, and method of generating a noise, may additionally comprise selecting means operable to select at least one of the sound signals. The selecting means may be operable to select two or more sound signals and advantageously be operable to select at least one of the two or more sound signals randomly.

At least one of the two or more selected sound recordings may be a sound clip of the selected sound signal. The, or each, sound clip may be less than or equal to half the length of the selected sound signal. The, or each, sound clip may be randomly selected from the length of the respective selected sound signal. The, or each, sound clip is preferably one second, or less, in duration. The duration of the, or each, sound clip may be determined randomly.

The amplitude of at least one of the two or more selected sound signals may be altered. The at least one selected sound recording having altered amplitude maybe randomly selected. The altered amplitude may be determined randomly.

The sound signals may comprise speech or any other sound suitable for creating desired acoustic scene.

The noise generator, or method of generating a noise, may further comprise sound recording means operable to record the sound recordings prior to being stored in the

storage means.

The invention will now be described by way of example with reference to the following diagrams, of which:

Figure 1 is a schematic drawing of a noise generator according to the present invention;

Figure 2 is a schematic drawing of a Virtual Acoustic Background (VAB) signal generated by the noise generator of Figure 1 ;

Figure 3 a is a graphical representation of a typical speech signal;

Figure 3b is a graphical representation of a typical background noise signal.

Figure 3 c is a graphical representation of a typical combined signal of the speech and background signals of Figures 3 a and 3b, respectively.

Figure 3d is a graphical representation of a digital Voice Activity Detector (VAD) signal;

Figure 3e is a graphical representation of a simple Virtual Acoustic Background (VAB) signal;

Figure 4 is a schematic drawing of a communication device according to the present invention.

Referring to Figure 1, a noise generator 10, according to the present invention, comprises signal processing means 12 for receiving one or more sound signals 14.

The signal processing means 12 adapts the received sound signals 14 to generate a virtual acoustic background (VAB) signal 18 which simulates a predetermined acoustic scene.

The sound signals 14 may be either live sound signals 20 or recorded sound signals 22, or both. The live sound signals are transmitted from a live source 24 and the recorded sound signals 22 are stored on storage means 26, such as, for example, a hard disk drive or solid state digital media storage, or the like. The storage means 16 may be located within the noise generator 10, or alternatively, located remotely from the noise generator, depending on which is most suitable for situation in which the noise generator is being used.

It will be appreciated that for particular applications, as described below, the one or more received sound signals 14 are solely recorded sound signals 22 derived from the storage means 26. Similarly, it will be appreciated that for other applications, as described below, the one or more received sound signals 14 are solely live sound signals 20, derived from the live source 24. Similarly, it will be appreciated that for other applications described below, the received sound signals 14 may be a combination of live sound signals 20 and recorded sound signals 22.

The context of the sound signals 14 is dependent on the desired acoustic scene, which it is intended to portray. For example, to portray an acoustic scene of a busy office, or call centre, the sound recordings would include speech and perhaps telephones ringing. Alternatively, if, for example, the acoustic scene to be conveyed relates to travelling then the sound recordings 14 may be, for example, aircraft taking-off, a departure lounge announcement, or alternatively, sounds of motor vehicles or boats.

The noise generator 10, further comprises selecting means 16, disposed in the noise generator 10, which continuously and randomly selects the one or more sound signals 14 that form the VAB signal 18. The selecting means may be any suitable digital electronic circuitry for random selection.

The selecting means 16 is located within the noise generator 10. However, it will be appreciated that, if required, the selecting means may be located remotely from the noise generator 10, in which case selected sound signals would be transmitted to the noise generator over a communications network.

Referring also to Figure 2, in addition, or as an alternative, to selecting a complete sound signal 14, the selecting means randomly selects sound clips 28 from the sound signals 14. Further, the duration of each sound clip 28 and the portion of the respective sound signal 14, which forms the sound clip 28, are selected randomly.

Each sound clip 28 is less than half the duration of the complete sound signal 14 from. which it is derived and, depending on the context of the VAB signal 18 to be generated, some or all the sound clips 28 are less than one second in duration.

The selected sound signals 14 and/or sound clips 28 are summed, by the signal processing means 12, to generate a VAB signal 18.

An example of an algorithm which the signal processing means may use to generate the VAB signal, follows. However, it will be appreciated that other algorithms may be used within the working of the present invention.

The algorithm generates a random VAB signal from a finite set of sound signals 14. The set of sound signals are predetermined to relate contextually to a particular acoustic scene to be portrayed by the VAB signal. The algorithm is described in discrete time as it is implemented on a digital signal processing system.

Given a set of n sound signals, each of length L, W(i,j)(iεl : n, j<?l : L) , the algorithm generates a VAB signal by summing randomly selected sound signals and/or sound clips, of the n sound signals. The output of the algorithm at any time is formed from the sum of the contributions of each selected sound signal and/or sound clips.

In order to obtain the required randomness, each sound clip is taken from a different randomly selected portion of each respective sound signal and weighted with different amplitude.

The output at time k is given by:

y* = ∑lsmpM _h Start; + Index,] (1)

The pointer indices, Index,, are incremented after each selected sound signal and/or sound clip has terminated, such that the VAB signal is generated from the sum of continuous sound signals or sound clips selected at that particular moment in time. The start point within the duration of each selected sound signal, Starts is randomly chosen, along with the sound clip length, C _L eng _th , such that:

Start, + C ₁ ^ < L (2)

Following termination of each selected sound clip, the indices are compared with the relevant lengths of the sound signals in the set. If Index _t = C _Lenglh then Index, is reset

to 1 and a new C _Lenglhι and a new Amplitude _t are selected at random.

For practical purposes a lower limit on the length of the sound clip is useful. An upper limit on the start indices (e.g. to L/2) imposes an upper limit on the length of the clip, C _Length » by way of equation 2 above.

Figure 2 is a time line of sound signals 14 and/or sound clips 28, randomly selected for a period of time between t and t+x. The length of the sound signals 14 and/or sound clips 28 is randomly selected as is the portion of the original sound signal 14 from which each respective sound clip 28 is derived. The VAB signal 18 for the period of time x to x+t is the sum of the sound signals and/or sound clips continuously selected for that period at random. Because the VAB signal is formed of sound signals and/or sound clips which are derived from a real noise background which it is intended to portray, the real noise background is simulated. However, because the VAB signal is generated by summing a plurality of randomly selected and processed sound signals and/or clips, the VAB signal carries no discernable information content.

Real background noise may be picked up by a microphone of a telephone, from the surrounding environment, and undesirably transmitted to a third party with a voice signal and during periods when there is no voice signal. As described above, the real background noise will often carry sensitive and confidential information which may be understood and used by third parties to the detriment of the call centre company or customer thereof.

In applications, such as, for example, communication systems for call centres, the VAB signal 18 is substituted for, or combined with, real background noise.

Figure 3a shows a typical voice signal 130 and periods of silence 132 and Figure 3b shows a typical signal for real background noise 134. The microphone of a telephone is exposed to the sum of the voice signal 130 and the background noise signal 132, i.e. a real output signal 136, as shown in Figure 3c, such that:

output signal=voice signal + background noise signal

A Voice Activity Detector (VAD), known in the art, is used to determine when near end speech is present and when speech is absent. Figure 3d shows a VAD Boolean output, voice, signal 138 of a perfect VAD detecting activity in the speech component of the voice signal 130.

When near end speech is absent (voice = 0), the real background noise 134 is substituted by a VAB signal 118. An example of a simple VAB signal 118 is shown in Figure 3e.

Where there is a high signal to noise ratio (SNR) and a perfect VAD, the VAD is used to switch between real background noise signal 134 and the VAB signal 118, such that:

Combined output signal = voice signal * signal + (1 -voice) * VAB

Such a combined VAB/voice output signal 140 is shown in Figure 3f, wherein the real background noise 134 has been substituted with the VAB signal 118, during periods of speech inactivity.

In addition to the above, it will be appreciated that the signal processing means may alternatively adapt the VAB signal 118 and voice signal 130 such that the VAB signal 118 is continuously in the background of the speech signal and/or reduces in amplitude during periods of speech.

Referring to Figure 4, a communications device 200, such as a telephone, comprises a communicating microphone 242 and a communicating receiver 244. The communications device 200 further comprises a noise generator 210, as described above, having signal processing means 212.

The microphone 242 picks up the speech of the operator and the background noise, within the surrounding environment of the operator, which together form a combined input signal 246. Both the speech and the background noise are, ordinarily,

transmitted to the receiving party through the communications network. The speech signal contains discernable information content as it contains information which the operator intends the receiving party to understand. The background noise may also contain discernable information content, which may be intelligible to receiving party. However, it may be undesirable for the receiving party to receive the discernable information content of the background noise as it maybe confidential, for example, where the telephone conversation is taking place from a call centre of a bank. Alternatively, or additionally, the background noise may undesirably portray an environment which the operator does not wish to portray such as, for example, a quite office which may benefit from being perceived, by a receiving party, as a busy bustling office.

The term discernable information content is herein defined as information which is intelligible and a receiving party is capable of understanding and using to the detriment of the transmitting party. Similarly, the term no discernable information content is herein defined as information which is not intelligible and the receiving party is not capable of understanding and/or using to the detriment of the transmitting party.

The combined input signal 246 is fed to the noise generator 210, through a noise generator input 248 and to a controllable gain amplifier 250, through an amplifier input link 252.

The noise generator 210 generates a V AB signal 218, as described above. The controllable gain amplifier 250 is controlled in relation to the amplitude of the VAB

signal 218, such that the optimum signal to noise ration can be maintained between the voice signal and the VAB signal. The VAB signal is fed into the controllable gain amplifier 250 through a second amplifier input link 254.

The VAB signal 218 is fed to a second signal processor 256, which either combines the combined input signal 246 with, or substitutes for, the VAB signal 218 to form a transmitted signal 258. The transmitted signal 258 is such that the integrity of the original speech signal component of the transmitted signal 258 is maintained and the background noise/ VAB signal component of the transmitted signal 258 has no discernable information content but simulates the original background noise or a desired background noise.

The VAB signal 218 signal is also fed to the communicating receiver 244 through a first receiver input link 260. A received signal 262 is combined with the VAB signal 218 to enable an operator to monitor the VAB signal 218.

It will be appreciated that for the example of a bank call centre the emphasis will be on security and confidentiality and therefore the transmitted signal should have no discernable information content. However, for other applications, such as, for example, a quite office wishing to portray a busy environment or a mobile phone user, the emphasis will be on the creation of a VAB signal simulating a predetermined acoustic scene.

It will also be appreciated that the present invention is not limited to the application mentioned herein, but applicable to any application in which it is desirable to create a

virtual acoustic background having no discernable information content and portraying a predetermined acoustic scene.