Acoustic crosstalk cancellation

Circuitry for acoustic crosstalk cancellation between first and second acoustic signals, the circuitry comprising: crosstalk cancellation circuitry configured to: receive a first audio signal and, based on the received first audio signal, generate a first crosstalk cancellation signal; receive a second audio signal and, based on the received second audio signal, generate a second crosstalk cancellation signal; combine the first crosstalk cancellation signal with a signal indicative of the second audio signal to generate a first crosstalk cancellation circuitry output signal; and combine the second crosstalk cancellation signal with a signal indicative of the first audio signal to generate a second crosstalk cancellation circuitry output signal; and output stage circuitry configured to: receive the first crosstalk cancellation circuitry output signal and, based on the received first crosstalk cancellation circuitry, generate a first drive signal for driving a first speaker to generate the first acoustic signal; and receive the second crosstalk cancellation circuitry output signal and, based on the received second crosstalk cancellation circuitry, generate a second drive signal for driving a second speaker to generate the second acoustic signal, wherein a parameter of the crosstalk cancellation circuitry is variable based on one or more of: a position of a user of a host device incorporating the circuitry with respect to the host device; a volume setting of the host device; a level of the first and/or second crosstalk cancellation signal; and an operational parameter of the output stage circuitry.

FIELD OF THE INVENTION

The present disclosure relates to circuitry for acoustic crosstalk cancellation.

BACKGROUND

Stereo playback of audio signals typically involves delivering a left audio signal channel and a right audio signal channel to respective left and right speakers. However, stereo playback depends upon the left and right speakers being positioned sufficiently wide apart relative to the listener. In particular, there must be a relatively large difference between the angles of incidence of the respective acoustic signals from the left and right speakers in order for the listener's natural binaural stereo hearing to produce a stereo perception. This is because if playback occurs from two relatively closely spaced loudspeakers which present a relatively small difference in angle of incidence of the respective acoustic signals, then the acoustic signal from each respective speaker is also heard by the contralateral ear at a similar amplitude and with relatively little differential delay. This effect is known as acoustic crosstalk. The perceptual result of crosstalk is that perceived stereo cues of the played audio may be severely deteriorated, so that little or no stereo effect is perceived.

Acoustic crosstalk can be sufficiently avoided, and a stereo perception can be delivered to the listener(s), by placing the left and right speakers far apart relative to the listener(s), such as many meters apart at opposite sides of a room or theatre. However, this is not possible when using a physically compact audio playback device such as a smartphone or tablet computer, as the onboard speakers of such devices cannot be positioned far apart relative to the listener. In such devices the onboard speakers can be positioned no further apart than the furthest apart corners or sides of the respective device. Even if the device is brought inconveniently close to the listener in an attempt to increase the difference between the respective angles of incidence of the left and right acoustic signals to the listener's ears, this still fails to generate any significant stereo perception from the onboard speakers due to the small size of the compact device.

One way to achieve a suitable perceptible stereo playback when using compact playback devices is to use additional external speakers, such as headphone speakers or loudspeakers, driven from the playback device. However this introduces additional cost, size and weight of such external hardware and runs counter to the intended compact and lightweight mode of use of compact devices, while also reducing the achieved utility of the onboard speakers.

Attempts have been made to pre-process the left and right audio signal channels prior to playback in order to cancel acoustic crosstalk and provide the listener with a stereo perception when the speakers are relatively close together. However, these approaches have suffered from a number of problems including being highly sensitive to the position of the listener's head relative to the playback device, whereby even very slight head movements significantly diminish the perceived stereo effect and rapidly escalate spectral coloration producing unpleasant sound corruption, and also adding a substantial load on both transducers.

Additionally, existing acoustic crosstalk cancellation systems can lead to amplifier saturation and attendant distortion in the output acoustic signals. In general, such systems add a crosstalk cancellation signal to an input audio signal and output a combined audio and crosstalk cancellation signal to an amplifier of an output stage that drives a speaker. If the level of the combined audio and crosstalk cancellation signal is sufficiently high the amplifier may saturate, leading to distortion in the signal output by the amplifier and consequently to distortion in the acoustic signal output by the speaker.

Past attempts at acoustic crosstalk cancellation (XTC) have also suffered from a failure to optimise crosstalk cancellation evenly across the audio spectrum. It has been suggested to resolve this by frequency dependent regularisation involving hierarchical spectral division responsive to listening conditions, however this entails determining the frequency divisions and in turn complicates the crosstalk canceller design, which imports a significant processing burden and increased memory requirements, which is undesirable for typical compact playback devices. In particular the band branching method requires the input audio to be divided into numerous sub-bands, the widths of which are dependent on the playback geometry, sampling frequency etc. Then, each band is processed separately by a XTC design specifically for each band using a corresponding regularisation parameter. This is thus a complex XTC structure which undesirably increases processor and memory requirements of the crosstalk canceller.

SUMMARY

According to a first aspect, the invention provides circuitry for acoustic crosstalk cancellation between first and second acoustic signals, the circuitry comprising:crosstalk cancellation circuitry configured to:receive a first audio signal and, based on the received first audio signal, generate a first crosstalk cancellation signal;receive a second audio signal and, based on the received second audio signal, generate a second crosstalk cancellation signal;combine the first crosstalk cancellation signal with a signal indicative of the second audio signal to generate a first crosstalk cancellation circuitry output signal; andcombine the second crosstalk cancellation signal with a signal indicative of the first audio signal to generate a second crosstalk cancellation circuitry output signal; andoutput stage circuitry configured to:receive the first crosstalk cancellation circuitry output signal and, based on the received first crosstalk cancellation circuitry, generate a first drive signal for driving a first speaker to generate the first acoustic signal; andreceive the second crosstalk cancellation circuitry output signal and, based on the received second crosstalk cancellation circuitry, generate a second drive signal for driving a second speaker to generate the second acoustic signal,wherein a parameter of the crosstalk cancellation circuitry is variable based on one or more of:a position of a user of a host device incorporating the circuitry with respect to the host device;a volume setting of the host device;a level of the first and/or second crosstalk cancellation signal; andan operational parameter of the output stage circuitry.

The circuitry may further comprise user position detection circuitry configured to detect the position of the user with respect to the host device.

The user position detection circuitry may be configured to detect a distance and/or an angle of the user with respect to the host device.

The user position detection circuitry may be configured to detect the distance and/or angle of the user with respect to the host device based on one or more of:detected reflections of ultrasonic signals transmitted by a transducer of the host device; andimages generated by a camera of the host device.

The crosstalk cancellation circuitry may comprise:a first crosstalk cancellation filter for generating the first crosstalk cancellation signal; anda second crosstalk cancellation filter for generating the second crosstalk cancellation signal,wherein the user position detection circuitry is configured to output a coefficient control signal to the crosstalk cancellation circuitry to cause the crosstalk cancellation circuitry to adjust filter coefficients of the first and/or second crosstalk cancellation filters, based on the detected position of the user.

The crosstalk cancellation circuitry may be configured to select new filter coefficients for the first and/or second crosstalk cancellation filters from a memory based on the detected position of the user.

The crosstalk cancellation circuitry may be configured to calculate new filter coefficients for the first and/or second crosstalk cancellation filters based on the detected position of the user.

The circuitry may further comprise monitoring circuitry configured to monitor one or more operational parameters of the output stage circuitry.

The monitoring circuitry may be configured to output a level control signal to the crosstalk cancellation circuitry to adjust a level of the first and/or the second crosstalk cancellation signal if the monitoring circuitry detects, based on the one or more monitored operational parameters, that the output stage circuitry is at or is approaching a saturation state.

The monitoring circuitry may comprise circuitry for monitoring an output current and/or an output voltage associated with the output stage circuitry.

The monitoring circuitry may be configured to compare the monitored output current or output voltage to a predetermined current or voltage threshold to detect if the output stage circuitry is at or approaching a saturation state.

The monitoring circuitry may be configured to monitor the volume setting of the host device to output a level control signal to the crosstalk cancellation circuitry to adjust a level of the first and/or the second crosstalk cancellation signal if the volume setting meets or exceeds a predefined volume threshold.

The monitoring circuitry may be configured to monitor a level of the first and/or second crosstalk cancellation signal and to adjust the level of the first and/or second crosstalk cancellation signal if it is determined that the level of the first and/or second crosstalk cancellation signal could cause saturation of the output stage circuitry.

The circuitry may further comprise input filter circuitry configured to receive first and second input audio signals and to generate a first plurality of sub-band signals based on the first input audio signal and a second plurality of sub-band signals based on the second input audio signal.

The first audio signal received by the crosstalk cancellation circuitry may be based on a first sub-band signal of the first plurality of sub-band signals output by the input filter circuitry, and the second audio signal received by the crosstalk cancellation circuitry may be based on a first sub-band signal of the second plurality of sub-band signals output by the input filter circuitry.

The circuitry may further comprise equalisation circuitry configured to receive first and second input audio signals and to output first and second equalised audio signals to the crosstalk cancellation circuitry.

The equalisation circuitry may comprise:a first set of biquadratic filters configured to receive the first input audio signal and to output the first equalised audio signal; anda second set of biquadratic filters configured to receive the second input audio signal and to output the second equalised audio signal.

According to a second aspect, the invention provides an integrated circuit comprising the circuitry of the first aspect.

According to a third aspect, the invention provides a host device comprising circuitry according to the first aspect.

The host device may comprise a laptop, notebook, netbook or tablet computer, a gaming device, a games console, a controller for a games console, a virtual reality (VR) or augmented reality (AR) device, a mobile telephone, a portable audio player, a portable device, an accessory device for use with a laptop, notebook, netbook or tablet computer, a gaming device, a games console a VR or AR device, a mobile telephone, a portable audio player or other portable device.

According to a fourth aspect, the invention provides a crosstalk cancellation system for applying crosstalk cancellation to an audio signal, wherein a level of the crosstalk cancellation applied is variable based on one or more of:a volume setting of the host device;a level of a crosstalk cancellation signal to be applied to the audio signal; andan operational parameter of output stage circuitry for driving a transducer.

According to a fifth aspect, the invention provides a crosstalk cancellation system for applying crosstalk cancellation to an audio signal, wherein a parameter of the crosstalk cancellation applied is variable based on one or more of:a position of a user of a host device incorporating the circuitry with respect to the host device;a volume setting of the host device;a level of a crosstalk cancellation signal to be applied to the audio signal; andan operational parameter of output stage circuitry for driving a transducer.

According to a sixth aspect, the invention provides circuitry for acoustic crosstalk cancellation between first and second acoustic signals, the circuitry comprising:input filter circuitry configured to receive first and second audio input signals and to generate a first plurality of sub-band signals based on the first audio input signal and a second plurality of sub-band signals based on the second audio input signal; andcrosstalk cancellation circuitry configured to:generate a first crosstalk cancellation signal based on a first sub-band signal of the first plurality of sub-band signals;generate a second crosstalk cancellation signal based on a first sub-band signal of the second plurality of sub-band signals;combine the second crosstalk cancellation signal with a signal indicative of the first audio signal and a second sub-band signal of the first plurality of sub-band signals to generate a first crosstalk cancellation circuitry output signal; andcombine the first crosstalk cancellation signal with a signal indicative of the second audio signal and a second sub-band signal of the second plurality of sub-band signals to generate a second crosstalk cancellation circuitry output signal.

According to a seventh aspect, the invention provides circuitry for acoustic crosstalk cancellation between first and second acoustic signals, the circuitry comprising:crosstalk cancellation circuitry configured to:receive a first audio signal and, based on the received first audio signal, generate a first crosstalk cancellation signal; andreceive a second audio signal and, based on the received second audio signal, generate a second crosstalk cancellation signal; andposition detection circuitry configured to detect the position of a user of a host device incorporating the circuitry with respect to the host device, wherein the position detection circuitry is configured to output a control signal to cause adjustment of an operational parameter of the crosstalk cancellation circuitry based on the detected position of the user.

According to an eighth aspect, the invention provides circuitry for acoustic crosstalk cancellation between first and second acoustic signals, the circuitry comprising:crosstalk cancellation circuitry configured to:receive a first audio signal and, based on the received first audio signal, generate a first crosstalk cancellation signal; andreceive a second audio signal and, based on the received second audio signal, generate a second crosstalk cancellation signal; andoutput stage circuitry configured to:receive the first crosstalk cancellation circuitry output signal and, based on the received first crosstalk cancellation circuitry, generate a first drive signal for driving a first speaker to generate the first acoustic signal; andreceive the second crosstalk cancellation circuitry output signal and, based on the received second crosstalk cancellation circuitry, generate a second drive signal for driving a second speaker to generate the second acoustic signal,wherein the circuitry is configured to adjust a level of the first and/or the second crosstalk cancellation signal responsive to an indication of possible saturation of the output stage circuitry.

DETAILED DESCRIPTION

Referring first toFIG.1, a device such as a smartphone or tablet computer that is capable of audio playback is shown generally at100.

The device, shown generally at100, includes a housing110that includes first and second speaker ports112,114which, in the illustrated example, are provided at opposite ends of a front face120of the device100. As will be appreciated by those skilled in the art, in other examples the first and second speaker ports112,114may be positioned differently, e.g., in opposite ends of the housing110, or at opposite ends of a single side or end face of the housing110.

The device100also includes a microphone116, which in this example is positioned towards one end of the front face120of the device100, adjacent the second speaker port114. It will be appreciated that the device100may include one or more additional microphones116, which may be positioned, for example, in the front face120, in a side or end face of the housing110, or in any other convenient location.

The device100may further include one or more cameras118, positioned, for example, towards one end of the front face120of the device100, and/or on a rear face of the device100.

FIG.2is a schematic representation of internal components of the device100ofFIG.1.

As shown inFIG.2, the device100includes audio processor circuitry210for generating left and right audio output signals for driving speakers of the device100. The audio processor circuitry210may be implemented as a single integrated circuit (IC) and may be configured to perform signal processing operations (e.g. filtering, crosstalk cancellation) on one or more received audio data streams to generate the left and right audio output signals.

The microphone(s)116are coupled to inputs of the audio processor circuitry210.

The device100further includes left and right speakers212,214which are coupled to the audio processor circuitry210to receive the respective left and right audio output signals from the audio processor circuitry210. The left and right speakers212,214are mounted in the left and right speaker ports112,114of the device housing110.

The device100further includes memory220, coupled to the audio processor circuitry210, for storing data used by the audio processor circuitry210to generate the left and right audio output signals, e.g., audio data, filter coefficients or other parameters used in the signal processing operations performed by the audio processor circuitry210.

The device100further includes processing circuitry230coupled to the audio processor circuitry210. The processing circuitry230may be, for example, an applications processor of the device100.

As will be appreciated by those of ordinary skill in the art, a practical implementation of the device100will include additional components such as a battery, communications circuitry and the like, which are not relevant to the present disclosure and will not be described here for the sake of clarity and brevity.

Because of the small form factor of the device100, the physical distance between the speaker ports112,114(and thus between the left and right speakers212,214) is limited, and thus acoustic crosstalk can occur during playback of audio through the speakers212,214.

This is illustrated inFIG.3, which shows that acoustic signals from each speaker212,214are also received by the contralateral ear314,312of a user300of the device. Thus, a first left acoustic signal component LL (denoting left speaker to left ear) output by the left speaker212travels along a first propagation path from the left speaker212to the user's left ear312. A second left acoustic signal component LR (denoting left speaker to right ear) output by the left speaker212travels along a second propagation path from the left speaker212to the user's right ear314. Similarly, a first right acoustic signal component RR (denoting right speaker to right ear) output by the right speaker214travels along a third propagation path from the right speaker to the user's right ear314, and a second right acoustic signal component RL (denoting right speaker to left ear) output by the right speaker214travels along a fourth propagation path from the right speaker to the user's left ear312.

As will be appreciated, the second left acoustic signal component LR and the second right acoustic signal component RL are acoustic crosstalk signals, and as explained above, this acoustic crosstalk can severely degrade the user's perception of stereo effects in the acoustic signals output by the speakers212,214.

FIG.4is a schematic representation of example circuitry for acoustic crosstalk cancellation according to the present disclosure. The circuitry may be implemented in, or form part of, the audio processor circuitry210of a device100such as a mobile telephone, smartphone, tablet computer or other small form factor device capable of audio playback.

The circuitry, shown generally at400inFIG.4, includes input filter circuitry410, equalisation circuitry420, adaptive crosstalk cancellation circuitry430, output stage circuitry450, monitoring circuitry460and user position detection circuitry470.

The circuitry400receives left and right audio signals LAUDIO, RAUDIO from a stereo audio source (not shown) at respective left and right audio input terminals402,404.

The input filter circuitry410is configured to divide the left and right input audio signals LAUDIO, RAUDIO into a plurality of sub-band signals. To this end, the input filter circuitry410includes a first plurality of filters which each receive the right input audio signal RAUDIO and a second plurality of filters which each receive the left input audio signal LAUDIO.

Thus, in the illustrated example the first plurality of filters comprises a first high-pass filter412and a first low-pass filter414which each receive the left input audio signal LAUDIO. The first high-pass filter412passes frequency components of the left input audio signal LAUDIO at frequencies above a threshold frequency to output a first high frequency sub-band signal, and the first low-pass filter414passes frequency components of the left input audio signal LAUDIO at frequencies below the threshold frequency to output a first low frequency sub-band signal.

Similarly, the second plurality of filters comprises a second high-pass filter416and a second low-pass filter, which each receive the right input audio signal RAUDIO. The second high-pass filter416passes frequency components of the right input audio signal RAUDIO at frequencies above the threshold frequency to output a second high frequency sub-band signal, and the second low-pass filter418passes frequency components of the right input audio signal RAUDIO at frequencies below the threshold frequency, to output a second low frequency sub-band signal.

In the illustrated example the first and second pluralities of filters each comprise two filters, but it will be appreciated by those of ordinary skill in the art that the input filter circuitry410could include any number of filters for dividing the input audio signals LAUDIO, RAUDIO into a plurality of sub-band signals with different frequency content.

The equalisation circuitry420is configured to process the sub-band signals output by the input filter circuitry410to maintain the spectral coloration of the input audio signals LAUDIO, RAUDIO. To this end the equalisation circuitry420includes first and second equalisation filters422,424(or sets of equalisation filters, where a set of equalisation filters comprises one or more equalisation filters). The equalisation filters may be, for example, biquadratic filters.

The first equalisation filter422receives the first low frequency sub-band signal output by the first low-pass filter414, and outputs a first equalised (or, more accurately, pre-equalised) signal to the adaptive crosstalk cancellation circuitry430. Similarly, the second equalisation filter424receives the second low frequency sub-band signal output by the second low-pass filter418, and outputs a second equalised (or, more accurately, pre-equalised) signal to the adaptive crosstalk cancellation circuitry430.

The adaptive crosstalk cancellation circuitry430is configured to receive the first and second equalised signals output by the equalisation circuitry420, and to output first and second crosstalk canceller output signals that compensate, at least partially, for the acoustic crosstalk between the acoustic signals output by the left and right speakers212,214of the device100and the user's opposite ears314,312, such that the acoustic crosstalk signals that arrive at the user's ears from the opposite speaker (i.e. the acoustic crosstalk signal RL that travels along the propagation path from the right speaker214to the user's left ear312and the acoustic crosstalk signal LR that travels along the propagation path from the left speaker212to the user's right ear314) are at least partially cancelled or attenuated.

The adaptive crosstalk cancellation circuitry430thus includes a first audio output signal filter432and a first crosstalk cancellation filter434, which each receive the equalised signal output by the first equalisation filter422. The adaptive crosstalk cancellation circuitry430further includes a second audio output signal filter436and a second crosstalk cancellation filter438, which each receive the equalised signal output by the second equalisation filter424.

The first audio output signal filter432is configured to generate, based on the received equalised signal, an audio signal ll representative of the acoustic signal component LL, and this audio signal ll is output by the first audio output signal filter432to a first input of a first summing node442of the adaptive crosstalk cancellation circuitry430.

The first crosstalk cancellation filter434is configured to generate, based on the received equalised signal, a first crosstalk cancellation signal −lr, which is an audio signal representative of the inverse of the acoustic signal component LR, and this audio signal −lr is output by the first crosstalk cancellation filter434to a first input of a second summing node444of the adaptive crosstalk cancellation circuitry430.

The second audio output signal filter436is configured to generate, based on the received equalised signal, an audio signal rr representative of the acoustic signal component RR, and this audio signal rr is output by the second audio output signal filter436to a second input of the second summing node444.

The second crosstalk cancellation filter438is configured to generate, based on the received equalised signal, a second crosstalk cancellation signal −rl, which is an audio signal representative of the inverse of the acoustic signal component RL, and this audio signal −rl is output by the second crosstalk cancellation filter438to a second input of the first summing node442.

The first summing node442also receives the first high frequency sub-band signal output by the first high-pass filter412of the input filter circuitry410, and the second summing node444also receives the second high frequency sub-band signal output by the second high-pass filter416of the input filter circuitry410.

Thus, the first summing node442is configured to output a signal including the first high frequency sub-band signal and components ll and −rl, while the second summing node444is configured to output a signal including the second high frequency sub-band signal and components rr and −lr.

It will be noted that the first and second high frequency sub-band signals output, respectively, by the first and second high-pass filters412,416of the input filter circuitry410are not processed by the equalisation circuitry420or by the adaptive crosstalk cancellation circuitry430, but are instead added to the outputs of the filters of the adaptive crosstalk cancellation circuitry430. By applying crosstalk cancellation processing only to the low frequency sub-bands of the input audio signals in this manner it may be possible to reduce or avoid audio coloration that may otherwise be introduced into the acoustic output signals as a result of applying crosstalk cancellation processing to the full-band input audio signals, as the higher frequency sub-bands of the input audio signals that may give rise to such audio coloration are not processed by the adaptive crosstalk cancellation circuitry430.

In alternative examples of the circuitry400, the input filter circuitry410may be omitted, in which case the equalisation circuitry420receives and processes the left and right input audio signals LAUDIO, RAUDIO rather than any sub-band signals, and no separate high frequency sub-band signals are received by the first or second summing nodes442,444.

The output stage circuitry450comprises first amplifier circuitry452and second amplifier circuitry454. The first amplifier circuitry452is configured to receive the signal output by the first summing node442and, based on this received signal, generate and output a drive signal for driving a first speaker (e.g., a left speaker212) of a host device incorporating the circuitry400. Similarly, the second amplifier circuitry454is configured to receive the signal output by the second summing node444and, based on this received signal, generate and output a drive signal for driving a second speaker (e.g., a right speaker214) of the host device.

The monitoring circuitry460is configured to monitor one or more operational parameters such as an output signal level of the output stage circuitry450, to detect if one or both of the first and second amplifier circuitry452,454is at or approaching a saturation state.

If the monitoring circuitry460detects (based on the monitored operational parameter(s)) that one or both of the first and second amplifier circuitry452,454is at or approaching a saturation state, it may output a level control signal to the adaptive crosstalk cancellation circuitry430, to cause the adaptive crosstalk cancellation circuitry430to adjust a level of one or both of the crosstalk cancellation signals −lr, −rl, to reduce the signal level of the signal(s) received at the input of the first and/or second amplifier circuitry452,454to a level at which saturation of the amplifier circuitry452,454can be avoided.

In some examples, the monitoring circuitry460may include circuitry for monitoring an output voltage and/or an output current of the first and/or second amplifier circuitry452,454and comparing the output voltage and/or current to one or more predefined voltage and/or current thresholds to detect whether the first and/or second amplifier circuitry452,454is at or approaching a saturation state.

Thus, if the monitored output voltage and/or current of one or both of the first and second amplifier circuitry452,454meets or exceeds a predefined threshold, the monitoring circuitry460may output the level control signal to the adaptive crosstalk cancellation circuitry430to cause the adaptive crosstalk cancellation circuitry430to adjust the signal level of the crosstalk cancellation signal(s) −lr, −rl as described above.

Additionally or alternatively, the monitoring circuitry460may be configured to monitor a volume setting of the host device and to output a level control signal to the adaptive crosstalk cancellation circuitry430to cause the adaptive crosstalk cancellation circuitry430to adjust the signal level of the crosstalk cancellation signal(s) −lr, −rl as described above if the volume setting meets or exceeds a predefined volume threshold.

For example, the monitoring circuitry460may be configured to monitor a volume control signal output by the processing circuitry230to determine the volume setting of the device, and based on this volume control signal determine whether an adjustment to the level of the crosstalk cancellation signals −lr, −ll is required to avoid saturation of the amplifier circuitry452,454.

In some examples the monitoring circuitry460may monitor a level of the crosstalk cancellation signals −lr, −ll in addition to monitoring the volume setting of the device, to determine whether the level of the signals received at the first and second amplifier circuitry452,454could cause saturation of the first and/or second amplifier circuitry452,454. If so, the monitoring circuitry460may output the level control signal to the adaptive crosstalk cancellation circuitry430to cause the adaptive crosstalk cancellation circuitry430to adjust the signal level of the crosstalk cancellation signal(s) −lr, −rl as described above.

By adjusting the level of the crosstalk cancellation signals −lr, −ll based on one or more operational parameters of the output stage circuitry450, and/or based on a volume setting of the host device, and/or based on the level of one or both of the crosstalk cancellation signals −lr, −rl in this way, saturation of the amplifier circuitry452,454and the attendant distortion in the acoustic signals output by the speakers212,214can be avoided.

The user position detection circuitry470is configured to detect a position, e.g. a distance and/or an angle, of a user with respect to the speakers212,214or some other reference point of the host device, and to output a coefficient control signal to the adaptive crosstalk cancellation circuitry430to cause the adaptive crosstalk cancellation circuitry430to dynamically adjust filter coefficients of the first and/or second crosstalk cancellation filters434,438based on the detected position of the user.

In some examples a plurality of sets of filter coefficients for the second and fourth crosstalk cancellation filters are stored in a memory (e.g. memory220). In response to the coefficient control signal, the adaptive crosstalk cancellation circuitry430may retrieve from the memory a set of filter coefficients suitable for the detected distance and/or angle of the user with respect to the host device, and apply the retrieved set of coefficients to the first and/or second crosstalk cancellation filters434,438.

The plurality of sets of filter coefficients may be stored in a lookup table in the memory, indexed by distance and/or by angle. The coefficient control signal output by the user position detection circuitry470may be representative of the detected distance and/or the detected angle, and the adaptive crosstalk cancellation circuitry430may select a new set of filter coefficients from the lookup table based on the detected distance and/or the detected angle, as represented by the coefficient control signal.

Alternatively, the adaptive crosstalk cancellation circuitry430may be configured to calculate new filter coefficients for the first and/or second crosstalk cancellation filters434,438on the fly based on the coefficient control signal, and to apply the determined filter coefficients to the first and/or second crosstalk cancellation filters434,438.

By dynamically adjusting the filter coefficients of the first and/or second crosstalk cancellation filters434,438based on the detected distance and/or angle of the user with respect to the host device, the crosstalk cancellation signals −rl, −lr output by the crosstalk cancellation filters434,438can be tuned to optimise (or at least improve) the crosstalk cancellation effect for a wide range of user positions relative to the host device, thereby increasing the size of the “sweet spot” within which stereo effects in the acoustic signals output by the speakers are perceptible to a user of a host device incorporating the circuitry400. In other words, the dynamic adjustment of the filter coefficients allows the user to perceive the stereo effects in the acoustic signals output by the speakers212,214at a greater range of relative distances and/or angles of the user with respect to the host device than in existing crosstalk cancellation systems.

The user position detection circuitry470may be configured to detect the position (distance and/or angle) of the user with respect to the host device in a number of different ways. For example, the user position detection circuitry470may detect the position of the user by processing reflections, detected by the microphone(s)116, of ultrasonic signals transmitted by one or both of the speakers212,214. Additionally or alternatively, the user position detection circuitry470may detect the position of the user based on images generated by the camera118and processed by the processing circuitry230. Those of ordinary skill in the art will be aware of other methods for detecting the position of a user relative to the host device which could be employed by the user position detection circuitry470.

The circuitry described above with reference to the accompanying drawings may be incorporated in a host device such as a laptop, notebook, netbook or tablet computer, a gaming device such as a games console or a controller for a games console, a virtual reality (VR) or augmented reality (AR) device, a mobile telephone, a portable audio player or some other portable device, or may be incorporated in an accessory device for use with a laptop, notebook, netbook or tablet computer, a gaming device, a VR or AR device, a mobile telephone, a portable audio player or other portable device.