Patent Description:
Audio signals can allow a listener to perceive a spatial sense in the sound field. However, many non-ideally configured stereo rendering systems employ moderately to severely unmatched drivers, which are mismatched by frequency response, output power, directionality, or any combination thereof. One such common example system could be a mobile phone or tablet capable of stereo audio playback, but employing only one "broadband" micro-loudspeaker orthogonally firing in relation to a band-limited earpiece driver with low frequency attenuation below <NUM>. The spatial sense in the sound field may be lost or distorted when an audio signal is reproduced using unmatched drivers.

<CIT>) describes a system, a method, and a non-transitory computer readable medium for producing a sound with enhanced spatial detectability and a crosstalk simulation. The audio processing system receives a left and right input channel of an audio input signal, and performs an audio processing to generate an output audio signal. The system generates left and right spatially enhanced signals by gain adjusting side subband components and mid subband components of the left and right input channels. The audio processing system generates left and right crosstalk channels such as by applying a filter and time delay to the left and right input channels, and mixes the spatially enhanced channels with the crosstalk channels.

<CIT>) describes a method and apparatus for audio bass enhancement using stereo speakers. By filtering a baseband signal of an input signal whose frequency is lower than a blocking frequency calculated based on the distance between first and second speakers, delaying the filtered signal for a predetermined time period, combining a signal component of the input signal output from the first speaker and a signal component of the delayed signal output from the first speaker and making the combined signal component correspond to the first speaker, and combining a signal component of the input signal output from the second speaker and a signal component of the delayed signal output from the second speaker and making the combined signal component correspond to the second speaker, deep and rich audio bass can be provided by a simple operation without structural modification of speakers with respect to micro speakers in which audio bass reproduction is not conventionally performed efficiently.

Embodiments relate to providing a virtual stereo audio reproduction (referred to herein as "VS-X") for non-ideally configured stereo rendering systems employing moderately to severely unmatched drivers, either by frequency response, output power, directionality, or any combination thereof.

In accordance with a first aspect of the present invention, there is provided a system for processing an input audio signal including a first plurality of channels, according to Claim <NUM>. The audio processing system includes a crossover network, a high frequency processor, and a low frequency processor. The crossover network separates an input audio signal into a low frequency signal and a high frequency signal. The high frequency processor applies a subband spatial processing and b-chain processing to the high frequency signal to spatially enhance the input signal, and adjust the input signal for the unmatched speakers. The low frequency processor applies a parametric band-pass filter and a first gain to the low frequency signal to generate a low frequency resonator signal, and a second gain to the low frequency signal to generate a low frequency passthrough signal. A combiner generates an output signal by combining the low frequency output signal with one of a left channel of the high frequency output signal for the left speaker or a right channel of the high frequency output signal for the right speaker. For example, if the left speaker handles lower frequencies than the right speaker, then the low frequency output signal is provided to the left speaker. In another example, if the right speaker handles lower frequencies than the left speaker, then the low frequency output signal is provided to the right speaker.

In accordance with a second aspect of the present invention, there is provided a computer-implemented method of processing an input audio signal including a first plurality of channels, according to Claim <NUM>. The method includes, by a computing system: separating the input audio signal into a low frequency signal and a high frequency signal; applying a b-chain processing to the high frequency signal to adjust for an asymmetry between a left speaker and a right speaker to generate a high frequency output signal; applying a parametric band-pass filter and a first gain to the low frequency signal to generate a low frequency resonator signal; applying a second gain to the low frequency signal to generate a low frequency passthrough signal; generating a low frequency output signal by combining the low frequency resonator signal with the low frequency passthrough signal; and generating an output signal by combining the low frequency output signal with one of a left channel of the high frequency output signal for the left speaker or a right channel of the high frequency output signal for the right speaker.

In accordance with a third aspect of the present invention, there is provided a non-transitory computer-readable storage medium comprising instructions which, when executed by a computer, causes the computer to carry out the method of the second aspect.

The figures depict, and the detailed description describes, various non-limiting embodiments for purposes of illustration only.

However, the described embodiments may be practiced without these specific details.

Example embodiments relate to providing a virtual stereo audio reproduction (referred to herein as "VS-X") for non-ideally configured stereo rendering systems employing moderately to severely unmatched drivers, such as by frequency response, output power, directionality, or any combination thereof. VS-X is an audio signal processing algorithm designed to restore and enhance the perceived spatial sound stage on such non-ideally configured stereo rendering systems. A primary role of the VS-X system is to address time alignment and frequency response asymmetries between loudspeakers in such a way as to create a stable non-spatial image (e.g. voice and bass guitar in a stereo mix), perceptually positioned at the ideal location directly in front of the listener's head. It also helps to create a stable and symmetric spatial image (e.g. balanced left/right components in a stereo mix, etc.). Further, by correcting the above asymmetries in the system, it provides the opportunity to apply increased immersion via sound stage enhancement techniques, such as subband spatial processing and crosstalk cancellation. The result of an optimally tuned VS-X system is an enhanced and spatially immersive transaural sound field, as perceived from the ideal listener "sweet spot.

Figure (<FIG> is an example of a mobile device <NUM> with non-ideal audio rendering, in accordance with some embodiments. The mobile device <NUM> includes a left speaker <NUM> (or <NUM>L) and a right speaker 110R (or <NUM>R). The speakers <NUM> and 110R are mismatched. For instance, the speaker <NUM> may be an earpiece driver with significant low frequency attenuation below <NUM>. The speaker 110R may be a "broad-band" micro-loudspeaker capable of rendering low and mid-frequency energy below <NUM> to <NUM>. Furthermore, the speaker 110R has more output power than the speaker <NUM>, and is orthogonally firing with respect to the speaker <NUM>. The speakers <NUM> and 110R may be mismatched with respect to the listener <NUM> in terms of frequency response, output power, directionality, or any combination thereof.

<FIG> is a schematic block diagram of an audio processing system <NUM>, in accordance with some example embodiments. The audio processing system <NUM> compensates for mismatch between a left speaker <NUM> and a right speaker 110R in terms of frequency response, output power, directionality, or any combination thereof. The audio processing system <NUM> receives an input audio signal X including a left input channel XL (or XL) and right input channel XR (or XR), and generates an output audio signal O including a left output channel OL (or OL) for the left speaker <NUM> and a right output channel OR (or OR) for the right speaker 110R.

The audio processing system <NUM> includes a crossover network <NUM> that is coupled to a low frequency processor <NUM> and a high frequency processor <NUM>. The crossover network <NUM> receives the left input channel XL and right input channel XR, and creates low frequency and high frequency channels. For example, the crossover network <NUM> includes filters that create low frequency (LF) channels including a left channel LFL (or LFL) and a right channel LFR (or LFR), and high frequency (HF) channels including a left channel HFL (or HFL), and a right channel HFR (or HFR). The left channel LFL is generated from the low frequency portions of the left input channel OL, and a right channel LFR is generated from the low frequency portions of the right input channel OR. The left channel LFL and the right channel LFR collectively form a low frequency signal <NUM>. The left channel HFL and the right channel HFR collectively form a high frequency signal <NUM>.

The low frequency signal <NUM> is processed by the low frequency processor <NUM>, and the high frequency signal <NUM> is processed by the high frequency processor <NUM>. As such, the audio processing system <NUM> treats the low frequency signal <NUM> independently from and in parallel to the counterpart high frequency signal <NUM>.

Assuming the non-ideal nature of a given stereo audio system, the ability of the listener <NUM> to perceive the device <NUM> as rendering a spatially immersive sound field from the vantage of a "sweet spot" depends on the treatment of the mid and high frequency audio bands, where both speakers <NUM>L and <NUM>R can be employed in combination. To that end, the high frequency processor <NUM> performs subband spatial enhancement, b-chain processing, equalization filtering, and amplification on the high frequency signal <NUM>.

The high frequency processor <NUM> includes a spatial enhancement processor <NUM>, a b-chain processor <NUM>, a high frequency (HF) equalization (EQ) filter <NUM>, and a high frequency gain <NUM>. The spatial enhancement processor <NUM> receives the left channel HFL and the right channel HFR, and processes these channels to generate a spatially enhanced signal A including a left spatially enhanced channel AL and a right spatially enhanced channel AR. In some embodiments, the spatial enhancement processor <NUM> applies a subband spatial processing that includes gain adjusting mid and side subband components of the high frequency signal <NUM> (including the left channel HFL and the right channel HFR). The spatial enhancement processor <NUM> may further perform a crosstalk compensation and a crosstalk cancellation. Additional details regarding the spatial enhancement processor <NUM> are discussed below in connection with <FIG>, <FIG>, <FIG> and <FIG>.

The b-chain processor <NUM> is coupled to the spatial enhancement processor <NUM>. "B-chain processing," as used herein, refers to processing of an audio signal that adjusts for mismatch of at least two speakers (e.g., left and right speakers) in terms of frequency response, output power, directionality, etc. The b-chain processor <NUM> adjusts for mismatch between the speakers <NUM>L and <NUM>R. Among other things, the b-chain processor <NUM> can adjust for overall time delay difference between speakers <NUM>L and <NUM>R and the listener's head, signal level (perceived and objective) difference between the speakers <NUM>L and <NUM>R and the listener's head, and frequency response difference between the speakers <NUM>L and <NUM>R and the listener's head. The b-chain processor <NUM> receives the left spatially enhanced channel AL and a right spatially enhanced channel AR, and adjusts for various mismatches between the speakers <NUM>L and <NUM>R to generate a left channel BL and a right channel BR. Additional details regarding the b-chain processor <NUM> are discussed below in connection with <FIG>.

The HF EQ filter <NUM> is coupled to the b-chain processor <NUM>. The HF EQ filter <NUM> receives the left channel BL and a right channel BR, and adjusts the relative level and frequency response of the left channel BL and the right channel BR. The HF EQ filter <NUM> can be used to provide additional flexibility in balancing the mix between the high and low frequency signals. In some embodiments, the HF EQ filter <NUM> is omitted. In some embodiments, the functionality of the HF EQ filter <NUM> is integrated with the b-chain processor <NUM>. For example, the N-band parametric EQ <NUM> may be configured to perform the functionality of the HF EQ filter <NUM>.

The HF gain <NUM> is coupled to the HF EQ filter <NUM>. The HF gain <NUM> receives the output of the HF EQ filter <NUM>, and adjusts the overall signal level of the high frequency signal relative to the low frequency signal and its signal path through the low frequency processor <NUM>. In some embodiments, different gains are applied to the left channel and the right channel of the high frequency signal by the HF gain <NUM>. The output of the HF gain <NUM> represents the output of the high frequency processor <NUM>, and includes a left high frequency output channel HFOL and a right high frequency output channel HFOR. The left channel HFOL and the right channel HFOR represent a spatially-enhanced transaural image that is combined with the low frequency signal <NUM> subsequent to processing by the low frequency processor <NUM>.

The low frequency processor <NUM> provides a stable non-spatial image (e.g., centerpanned elements) and sufficient punch and body to the perceived overall sound field while avoiding excessive low frequency energy that may degrade and mask the effects of the spatially-enhanced transaural image. The low frequency processor <NUM> includes a combiner <NUM>, a low frequency (LF) boost resonator <NUM>, an LF boost gain <NUM>, a LF passthrough gain <NUM>, and a combiner <NUM>. The combiner <NUM> is coupled to the crossover network <NUM> and receives the left channel LFL and the right channel LFR. The combiner <NUM> is further coupled to the LF boost resonator <NUM> and the LF passthrough gain <NUM>. The LF boost resonator <NUM> is coupled to the LF boost gain <NUM>. The LF boost gain <NUM> and LF passthrough gain <NUM> are coupled to the combiner <NUM>.

The combiner <NUM> combines the left channel LFL and the right channel LFR to generate the low frequency signal <NUM> (also shown as "LFS" in <FIG>). In some embodiments, a phase adjustment such as polarity inversion, Hilbert transform, or Allpass filter, may be applied to the left channel LFL and the right channel LFR prior to combination by the combiner <NUM> to compensate for any phase shifts introduced by the filters in the crossover network <NUM>.

Subsequent to the combination, the low frequency signal <NUM> is split into two parallel low frequency paths for processing: a resonator path including the LF boost resonator <NUM> and LF boost gain <NUM>, and a passthrough path including the LF passthrough gain <NUM>. The LF boost resonator <NUM> may be a parametric low-frequency band-pass filter, and the LF boost gain <NUM> applies a gain or attenuation on the output of the LF boost resonator <NUM>. The resonator path enhances the bass in such a way that low/mid frequency transients in the mix (e.g., kick drum and bass guitar attacks) or other targeted parts of the low/mid frequency spectrum are made to perceptually stand out. The resonator path additionally may further condition the low frequency signal <NUM> to suit the frequency response characteristics of a given system's "broadband" micro-loudspeaker (e.g., speaker <NUM>R), for optimal performance. The resonator path results in a low frequency resonator signal LFR.

In the passthrough path, the LF passthrough gain <NUM> attenuates the overall low frequency signal band enough to minimize negative impacts the non-enhanced low frequency signal <NUM> may have on the primarily mid and high frequency transaural sound field, while still providing enough broad low-frequency energy to prevent the stereo mix from sounding "anemic. " The pass-through path results in a low frequency passthrough signal LFP.

The combiner <NUM> combines the low frequency resonator signal LFR and the low frequency passthrough signal LFP to generate a low frequency output signal LFO. For example, the combiner <NUM> sums the signals LFR and LFP to generate the signal LFO. The combiner <NUM> may be coupled to the micro-loudspeaker to route the signal LFO to the appropriate micro-loudspeaker capable of reproducing low frequency content.

With reference back to <FIG>, for example, the speaker <NUM> may be an earpiece driver with significant low frequency attenuation below <NUM>, while the speaker 110R be the "broad-band" micro-loudspeaker capable of rendering low and mid-frequency energy down to <NUM>. Here, the low frequency output signal LFO is routed to the micro-loud speaker 110R, and not the earpiece speaker <NUM>. The left high frequency output channel HFOL is transmitted to the left speaker <NUM> as the output channel OL. The right high frequency output channel HFOR is combined with the low frequency output signal LFO to generate an output channel OR, which is transmitted to the right speaker 110R. In an example where the speaker <NUM> handles lower frequencies than the speaker 110R, the low frequency output signal LFO may be routed to the speaker <NUM> instead of the speaker 110R.

<FIG> is a schematic block diagram of a spatial enhancement processor <NUM>, in accordance with some embodiments. The spatial enhancement processor <NUM> spatially enhances an input audio signal, and performing crosstalk cancellation on spatially enhanced audio signal. To that end, the spatial enhancement processor <NUM> receives the high frequency signal <NUM> including the left high frequency channel HFL and the right high frequency channel HFR.

The spatial enhancement processor <NUM> generates the spatially enhanced signal A including the left spatially enhanced channel AL and the right spatially enhanced channel AR by processing the input channels HFL and HFR. The output audio signal A is a spatially enhanced audio signal of the high frequency signal <NUM> with crosstalk compensation and crosstalk cancellation. Although not shown in <FIG>, the spatial enhancement processor <NUM> may further include an amplifier that amplifies the output audio signal A from the crosstalk cancellation processor <NUM>, and provides the signal A to output devices, such as the loudspeakers <NUM>L and <NUM>R, that convert the output channels AL and AR into sound.

The spatial enhancement processor <NUM> includes a subband spatial processor <NUM>, a crosstalk compensation processor <NUM>, a combiner <NUM>, and a crosstalk cancellation processor <NUM>. The spatial enhancement processor <NUM> performs crosstalk compensation and subband spatial processing of the input channels HFL and HFR, combines the result of the subband spatial processing with the result of the crosstalk compensation, and then performs a crosstalk cancellation on the combined signals.

The subband spatial processor <NUM> includes a spatial frequency band divider <NUM>, a spatial frequency band processor <NUM>, and a spatial frequency band combiner <NUM>. The spatial frequency band divider <NUM> is coupled to the input channels HFL and HFR and the spatial frequency band processor <NUM>. The spatial frequency band divider <NUM> receives the left input channel HFL and the right input channel HFR, and processes the input channels into a spatial (or "side") component Xs and a nonspatial (or "mid") component Xm. For example, the spatial component Xs can be generated based on a difference between the left input channel HFL and the right input channel HFR. The nonspatial component Xm can be generated based on a sum of the left input channel HFL and the right input channel HFR. The spatial frequency band divider <NUM> provides the spatial component Xs and the nonspatial component Xm to the spatial frequency band processor <NUM>.

The spatial frequency band processor <NUM> is coupled to the spatial frequency band divider <NUM> and the spatial frequency band combiner <NUM>. The spatial frequency band processor <NUM> receives the spatial component Xs and the nonspatial component Xm from spatial frequency band divider <NUM>, and enhances the received signals. In particular, the spatial frequency band processor <NUM> generates an enhanced spatial component Es from the spatial component Xs, and an enhanced nonspatial component Em from the nonspatial component Xm.

For example, the spatial frequency band processor <NUM> applies subband gains to the spatial component Xs to generate the enhanced spatial component Es, and applies subband gains to the nonspatial component Xm to generate the enhanced nonspatial component Em. In some embodiments, the spatial frequency band processor <NUM> additionally or alternatively provides subband delays to the spatial component Xs to generate the enhanced spatial component Es, and subband delays to the nonspatial component Xm to generate the enhanced nonspatial component Em. The subband gains and/or delays can be different for the different (e.g., n) subbands of the spatial component Xs and the nonspatial component Xm, or can be the same (e.g., for two or more subbands). The spatial frequency band processor <NUM> adjusts the gain and/or delays for different subbands of the spatial component Xs and the nonspatial component Xm with respect to each other to generate the enhanced spatial component Es and the enhanced nonspatial component Em. The spatial frequency band processor <NUM> then provides the enhanced spatial component Es and the enhanced nonspatial component Em to the spatial frequency band combiner <NUM>.

The spatial frequency band combiner <NUM> is coupled to the spatial frequency band processor <NUM>, and further coupled to the combiner <NUM>. The spatial frequency band combiner <NUM> receives the enhanced spatial component Es and the enhanced nonspatial component Em from the spatial frequency band processor <NUM>, and combines the enhanced spatial component Es and the enhanced nonspatial component Em into a left enhanced channel EL (or EL) and a right enhanced channel ER (or ER). For example, the left enhanced channel EL can be generated based on a sum of the enhanced spatial component Es and the enhanced nonspatial component Em, and the right enhanced channel ER can be generated based on a difference between the enhanced nonspatial component Em and the enhanced spatial component Es. The spatial frequency band combiner <NUM> provides the left enhanced channel EL and the right enhanced channel ER to the combiner <NUM>.

The crosstalk compensation processor <NUM> performs a crosstalk compensation to compensate for spectral defects or artifacts in the crosstalk cancellation. The crosstalk compensation processor <NUM> receives the input channels HFL and HFR, and performs a processing to compensate for any artifacts in a subsequent crosstalk cancellation of the enhanced nonspatial component Em and the enhanced spatial component Es performed by the crosstalk cancellation processor <NUM>. In some embodiments, the crosstalk compensation processor <NUM> may perform an enhancement on the nonspatial component Xm and the spatial component Xs by applying filters to generate a crosstalk compensation signal Z, including a left crosstalk compensation channel ZL (or ZL) and a right crosstalk compensation channel ZR (or ZR). In other embodiments, the crosstalk compensation processor <NUM> may perform an enhancement on only the nonspatial component Xm.

The combiner <NUM> combines the left enhanced channel EL with the left crosstalk compensation channel ZL to generate a left enhanced compensation channel TL (or TL), and combines the right enhanced channel ER with the right crosstalk compensation channel ZR to generate a right enhanced compensation channel TR (or TR). The combiner <NUM> is coupled to the crosstalk cancellation processor <NUM>, and provides the left enhanced compensation channel TL and the right enhanced compensation channel TR to the crosstalk cancellation processor <NUM>.

The crosstalk cancellation processor <NUM> receives the left enhanced compensated channel TL and the right enhanced compensation channel TR, and performs crosstalk cancellation on the channels TL, TR to generate the spatially enhanced signal A including the left spatially enhanced channel AL (or AL) and the right spatially enhanced channel AR (or AR).

Additional details regarding the subband spatial processor <NUM> are discussed below in connection with <FIG>, additional details regarding the crosstalk compensation processor <NUM> are discussed below in connection with <FIG>, and additional details regarding the crosstalk cancellation processor <NUM> are discussed below in connection with <FIG>.

<FIG> is a schematic block diagram of a subband spatial processor <NUM>, in accordance with some embodiments. The subband spatial processor <NUM> includes the spatial frequency band divider <NUM>, the spatial frequency band processor <NUM>, and the spatial frequency band combiner <NUM>. The spatial frequency band divider <NUM> is coupled to the spatial frequency band processor <NUM>, and the spatial frequency band processor <NUM> is coupled to the spatial frequency band combiner <NUM>.

The spatial frequency band divider <NUM> includes an L/R to M/S converter <NUM> that receives the left input channel HFL and a right input channel HFR, and converts these inputs into the spatial component Xs and the nonspatial component Xm. The spatial component Xs may be generated by subtracting the left input channel XL and right input channel XR. The nonspatial component Xm may be generated by adding the left input channel XL and the right input channel XR.

The spatial frequency band processor <NUM> receives the nonspatial component Xm and applies a set of subband filters to generate the enhanced nonspatial subband component Em. The spatial frequency band processor <NUM> also receives the spatial subband component Xs and applies a set of subband filters to generate the enhanced nonspatial subband component Em. The subband filters can include various combinations of peak filters, notch filters, low pass filters, high pass filters, low shelf filters, high shelf filters, bandpass filters, bandstop filters, and/or all pass filters.

In some embodiments, the spatial frequency band processor <NUM> includes a subband filter for each of n frequency subbands of the nonspatial component Xm and a subband filter for each of the n frequency subbands of the spatial component Xs. For n = <NUM> subbands, for example, the spatial frequency band processor <NUM> includes a series of subband filters for the nonspatial component Xm including a mid-equalization (EQ) filter <NUM>(<NUM>) for the subband (<NUM>), a mid EQ filter <NUM>(<NUM>) for the subband (<NUM>), a mid EQ filter <NUM>(<NUM>) for the subband (<NUM>), and a mid EQ filter <NUM>(<NUM>) for the subband (<NUM>). Each mid EQ filter <NUM> applies a filter to a frequency subband portion of the nonspatial component Xm to generate the enhanced nonspatial component Em.

The spatial frequency band processor <NUM> further includes a series of subband filters for the frequency subbands of the spatial component Xs, including a side equalization (EQ) filter <NUM>(<NUM>) for the subband (<NUM>), a side EQ filter <NUM>(<NUM>) for the subband (<NUM>), a side EQ filter <NUM>(<NUM>) for the subband (<NUM>), and a side EQ filter <NUM>(<NUM>) for the subband (<NUM>). Each side EQ filter <NUM> applies a filter to a frequency subband portion of the spatial component Xs to generate the enhanced spatial component Es.

Each of the n frequency subbands of the nonspatial component Xm and the spatial component Xs may correspond with a range of frequencies. For example, the frequency subband (<NUM>) may corresponding to <NUM> to <NUM>, the frequency subband(<NUM>) may correspond to <NUM> to <NUM>, the frequency subband(<NUM>) may correspond to <NUM> to <NUM>, and the frequency subband(<NUM>) may correspond to <NUM> to Nyquist frequency. In some embodiments, the n frequency subbands are a consolidated set of critical bands. The critical bands may be determined using a corpus of audio samples from a wide variety of musical genres. A long term average energy ratio of mid to side components over the <NUM> Bark scale critical bands is determined from the samples. Contiguous frequency bands with similar long term average ratios are then grouped together to form the set of critical bands. The range of the frequency subbands, as well as the number of frequency subbands, may be adjustable.

In some embodiments, the mid EQ filters <NUM> or side EQ filters <NUM> may include a biquad filter, having a transfer function defined by Equation <NUM>: <MAT>.

The biquad can then be used to implement any second-order filter with real-valued inputs and outputs. To design a discrete-time filter, a continuous-time filter is designed and transformed it into discrete time via a bilinear transform. Furthermore, compensation for any resulting shifts in center frequency and bandwidth may be achieved using frequency warping.

For example, a peaking filter may include an S-plane transfer function defined by Equation <NUM>: <MAT>.

The spatial frequency band combiner <NUM> receives mid and side components, applies gains to each of the components, and converts the mid and side components into left and right channels. For example, the spatial frequency band combiner <NUM> receives the enhanced nonspatial component Em and the enhanced spatial component Es, and performs global mid and side gains before converting the enhanced nonspatial component Em and the enhanced spatial component Es into the left spatially enhanced channel EL and the right spatially enhanced channel ER.

More specifically, the spatial frequency band combiner <NUM> includes a global mid gain <NUM>, a global side gain <NUM>, and an M/S to L/R converter <NUM> coupled to the global mid gain <NUM> and the global side gain <NUM>. The global mid gain <NUM> receives the enhanced nonspatial component Em and applies a gain, and the global side gain <NUM> receives the enhanced spatial component Es and applies a gain. The M/S to L/R converter <NUM> receives the enhanced nonspatial component Em from the global mid gain <NUM> and the enhanced spatial component Es from the global side gain <NUM>, and converts these inputs into the left enhanced channel EL and the right enhanced channel ER.

<FIG> is a schematic block diagram of a crosstalk compensation processor <NUM>, in accordance with some embodiments. The crosstalk compensation processor <NUM> receives left and right input channels HFL and HFR, and generates left and right output channels by applying a crosstalk compensation on the input channels. The crosstalk compensation processor <NUM> includes a L/R to M/S converter <NUM>, a mid-component processor <NUM>, a side component processor <NUM>, and an M/S to L/R converter <NUM>.

The crosstalk compensation processor <NUM> receives the input channels HFL and HFR, and performs a preprocessing to generate the left crosstalk compensation channel ZL and the right crosstalk compensation channel ZR. The channels ZL, ZR may be used to compensate for any artifacts in crosstalk processing, such as crosstalk cancellation or simulation. The L/R to M/S converter <NUM> receives the left channel HFL and the right channel HFR, and generates the nonspatial component Xm and the spatial component Xs of the input channels XL, XR. The left and right channels may be summed to generate the nonspatial component of the left and right channels, and subtracted to generate the spatial component of the left and right channels.

The mid component processor <NUM> includes a plurality of filters <NUM>, such as m mid filters <NUM>(a), <NUM>(b), through <NUM>(m). Here, each of the m mid filters <NUM> processes one of m frequency bands of the nonspatial component Xm and the spatial component Xs. The mid component processor <NUM> generates a mid-crosstalk compensation channel Zm by processing the nonspatial component Xm. In some embodiments, the mid filters <NUM> are configured using a frequency response plot of the nonspatial component Xm with crosstalk processing through simulation. In addition, by analyzing the frequency response plot, any spectral defects such as peaks or troughs in the frequency response plot over a predetermined threshold (e.g., <NUM> dB) occurring as an artifact of the crosstalk processing can be estimated. These artifacts result primarily from the summation of the delayed and inverted contralateral signals with their corresponding ipsilateral signal in the crosstalk processing, thereby effectively introducing a comb filter-like frequency response to the final rendered result. The mid crosstalk compensation channel Zm can be generated by the mid component processor <NUM> to compensate for the estimated peaks or troughs, where each of the m frequency bands corresponds with a peak or trough. Specifically, based on the specific delay, filtering frequency, and gain applied in the crosstalk processing, peaks and troughs shift up and down in the frequency response, causing variable amplification and/or attenuation of energy in specific regions of the spectrum. Each of the mid filters <NUM> may be configured to adjust for one or more of the peaks and troughs.

The side component processor <NUM> includes a plurality of filters <NUM>, such as m side filters <NUM>(a), <NUM>(b) through <NUM>(m). The side component processor <NUM> generates a side crosstalk compensation channel Zs by processing the spatial component Xs. In some embodiments, a frequency response plot of the spatial component Xs with crosstalk processing can be obtained through simulation. By analyzing the frequency response plot, any spectral defects such as peaks or troughs in the frequency response plot over a predetermined threshold (e.g., <NUM> dB) occurring as an artifact of the crosstalk processing can be estimated. The side crosstalk compensation channel Zs can be generated by the side component processor <NUM> to compensate for the estimated peaks or troughs. Specifically, based on the specific delay, filtering frequency, and gain applied in the crosstalk processing, peaks and troughs shift up and down in the frequency response, causing variable amplification and/or attenuation of energy in specific regions of the spectrum. Each of the side filters <NUM> may be configured to adjust for one or more of the peaks and troughs. In some embodiments, the mid component processor <NUM> and the side component processor <NUM> may include a different number of filters.

In some embodiments, the mid filters <NUM> and side filters <NUM> may include a biquad filter having a transfer function defined by Equation <NUM>: <MAT>.

The biquad can then be used to implement a second-order filter with real-valued inputs and outputs. To design a discrete-time filter, a continuous-time filter is designed, and then transformed into discrete time via a bilinear transform. Furthermore, resulting shifts in center frequency and bandwidth may be compensated using frequency warping.

For example, a peaking filter may have an S-plane transfer function defined by Equation <NUM>: <MAT>.

Furthermore, the filter quality Q may be defined by Equation <NUM>: <MAT> where Δf is a bandwidth and fc is a center frequency.

The M/S to L/R converter <NUM> receives the mid crosstalk compensation channel Zm (or Zm) and the side crosstalk compensation channel Zs (or Zs), and generates the left crosstalk compensation channel ZL (or ZL) and the right crosstalk compensation channel ZR (or ZR). In general, the mid and side channels may be summed to generate the left channel of the mid and side components, and the mid and side channels may be subtracted to generate right channel of the mid and side components.

<FIG> is a schematic block diagram of a crosstalk cancellation processor <NUM>, in accordance with some embodiments. The crosstalk cancellation processor <NUM> receives the left enhanced compensation channel TL (or TL) and the right enhanced compensation channel TR (or TR) from the combiner <NUM>, and performs crosstalk cancellation on the channels TL, TR to generate the left output channel AL (or AL), and the right output channel AR (or AR).

The crosstalk cancellation processor <NUM> includes an in-out band divider <NUM>, inverters <NUM> and <NUM>, contralateral estimators <NUM> and <NUM>, combiners <NUM> and <NUM>, and an in-out band combiner <NUM>. These components operate together to divide the input channels TL, TR into in-band components and out-of-band components, and perform a crosstalk cancellation on the in-band components to generate the output channels AL, AR.

By dividing the input audio signal T into different frequency band components and by performing crosstalk cancellation on selective components (e.g., in-band components), crosstalk cancellation can be performed for a particular frequency band while obviating degradations in other frequency bands. If crosstalk cancellation is performed without dividing the input audio signal T into different frequency bands, the audio signal after such crosstalk cancellation may exhibit significant attenuation or amplification in the nonspatial and spatial components in low frequency (e.g., below <NUM>), higher frequency (e.g., above <NUM>), or both. By selectively performing crosstalk cancellation for the in-band (e.g., between <NUM> and <NUM>), where the vast majority of impactful spatial cues reside, a balanced overall energy, particularly in the nonspatial component, across the spectrum in the mix can be retained.

The in-out band divider <NUM> separates the input channels TL, TR into in-band channels TL,In, TR,In (or TL,In, TR,In) and out of band channels TL,Out, TR,Out (or TL,Out, TR,Out), respectively. Particularly, the in-out band divider <NUM> divides the left enhanced compensation channel TL into a left in-band channel TL,In and a left out-of-band channel TL,Out. Similarly, the in-out band divider <NUM> separates the right enhanced compensation channel TR into a right in-band channel TR,In and a right out-of-band channel TR,Out. Each in-band channel may encompass a portion of a respective input channel corresponding to a frequency range including, for example, <NUM> to <NUM>. The range of frequency bands may be adjustable, for example according to speaker parameters.

The inverter <NUM> and the contralateral estimator <NUM> operate together to generate a left contralateral cancellation component SL to compensate for a contralateral sound component due to the left in-band channel TL,In. Similarly, the inverter <NUM> and the contralateral estimator <NUM> operate together to generate a right contralateral cancellation component SR to compensate for a contralateral sound component due to the right in-band channel TR,In.

In one approach, the inverter <NUM> receives the in-band channel TL,In and inverts a polarity of the received in-band channel TL,In to generate an inverted in-band channel TL,In'. The contralateral estimator <NUM> receives the inverted in-band channel TL,In' (or TL,In'), and extracts a portion of the inverted in-band channel TL,In' corresponding to a contralateral sound component through filtering. Because the filtering is performed on the inverted in-band channel TL,In', the portion extracted by the contralateral estimator <NUM> becomes an inverse of a portion of the in-band channel TL,In attributing to the contralateral sound component. Hence, the portion extracted by the contralateral estimator <NUM> becomes a left contralateral cancellation component SL, which can be added to a counterpart in-band channel TR,In to reduce the contralateral sound component due to the in-band channel TL,In. In some embodiments, the inverter <NUM> and the contralateral estimator <NUM> are implemented in a different sequence.

The inverter <NUM> and the contralateral estimator <NUM> perform similar operations with respect to the in-band channel TR,In to generate the right contralateral cancellation component SR. Therefore, detailed description thereof is omitted herein for the sake of brevity.

In one example implementation, the contralateral estimator <NUM> includes a filter <NUM>, an amplifier <NUM>, and a delay unit <NUM>. The filter <NUM> receives the inverted input channel TL,In' and extracts a portion of the inverted in-band channel TL,In' corresponding to a contralateral sound component through a filtering function. An example filter implementation is a Notch or Highshelf filter with a center frequency selected between <NUM> and <NUM>, and Q selected between <NUM> and <NUM>. Gain in decibels (GdB) may be derived from Equation <NUM>: <MAT>.

The configurations of the crosstalk cancellation can be determined by the speaker parameters. In one example, filter center frequency, delay amount, amplifier gain, and filter gain can be determined, according to an angle formed between two speakers <NUM> and 110R with respect to a listener. In some embodiments, values between the speaker angles are used to interpolate other values.

The combiner <NUM> combines the right contralateral cancellation component SR to the left in-band channel TL,In to generate a left in-band compensation channel UL, and the combiner <NUM> combines the left contralateral cancellation component SL to the right in-band channel TR,In to generate a right in-band compensation channel UR. The in-out band combiner <NUM> combines the left in-band compensation channel UL with the out-of-band channel TL,Out to generate the left output channel AL, and combines the right in-band compensation channel UR with the out-of-band channel TR,Out to generate the right output channel AR.

Accordingly, the left output channel AL includes the right contralateral cancellation component SR corresponding to an inverse of a portion of the in-band channel TR,In attributing to the contralateral sound, and the right output channel AR includes the left contralateral cancellation component SL corresponding to an inverse of a portion of the in-band channel TL,In attributing to the contralateral sound. In this configuration, a wavefront of an ipsilateral sound component output by the speaker 110R according to the right output channel AR arrived at the right ear can cancel a wavefront of a contralateral sound component output by the loudspeaker <NUM>L according to the left output channel AL. Similarly, a wavefront of an ipsilateral sound component output by the speaker <NUM> according to the left output channel AL arrived at the left ear can cancel a wavefront of a contralateral sound component output by the speaker <NUM>R according to right output channel AR. Thus, contralateral sound components can be reduced to enhance spatial detectability.

<FIG> is a schematic block diagram of a b-chain processor <NUM>, in accordance with some embodiments. The b-chain processor <NUM> includes the speaker matching processor <NUM> and the delay and gain processor <NUM>. The speaker matching processor <NUM> includes an N-band equalizer (EQ) <NUM> coupled to a left amplifier <NUM> and a right amplifier <NUM>. The delay and gain processor <NUM> includes a left delay <NUM> coupled to a left amplifier <NUM>, and a right delay <NUM> coupled to a right amplifier <NUM>.

With reference to <FIG>, assuming the orientation of the listener <NUM> remains fixed towards the center of an ideal spatial image generated by the speakers <NUM>L and <NUM>R (e.g., the virtual lateral center of the sound stage, given symmetric, matched, and equidistant loudspeakers), the transformational relationship between the ideal and real rendered spatial image can be described based on (a) overall time delay between one speaker and the listener <NUM> being different from that of another speaker, (b) signal level (perceived and objective) between one speaker and the listener <NUM> being different from that of another speaker, and (c) frequency response between one speaker and the listener <NUM> being different from that of another speaker.

The b-chain processor <NUM> corrects the above relative differences in delay, signal level, and frequency response, resulting in a restored near-ideal spatial image, as if the listener <NUM> (e.g., head position) and/or rendering system were ideally configured.

Returning to <FIG>, the b-chain processor <NUM> receives as input the audio signal A including the left enhanced channel AL and the right enhanced channel AR from the spatial enhancement processor <NUM>. If the audio signal A has no spatial asymmetries and if no other irregularities exist in the system, the spatial enhancement processor <NUM> provides a dramatically enhanced sound stage for the listener <NUM>. However, if asymmetries do exist in the system, as illustrated by the mismatched speakers <NUM>L and <NUM>R in <FIG>, the b-chain processor <NUM> may be applied to retain the enhanced sound stage under non-ideal conditions.

Whereas the ideal listener/speaker configuration includes a pair of loudspeakers with matching left and right speaker-to-head distances, many real-world setups do not meet these criteria, resulting in a compromised stereo listening experience. Mobile devices, for example, may include a front facing earpiece loudspeaker with limited bandwidth (e.g. <NUM> - <NUM> frequency response), and an orthogonally (down or side-ward) facing micro-loudspeaker (e.g., <NUM> - <NUM> frequency response). Here, the speaker system is unmatched in a two-fold manner, with audio driver performance characteristics (e.g., signal level, frequency response, etc.) being different, and time alignment relative to the "ideal" listener position being un-matched because the non-parallel orientation of the speakers. Another example is where a listener using a stereo desktop loudspeaker system does not arrange either the loudspeakers or themselves in the ideal configuration. The b-chain processor <NUM> thus provides for tuning of the characteristics of each channel, addressing associated system-specific asymmetries, resulting in a more perceptually compelling transaural sound stage.

After spatial enhancement processing or some other processing has been applied to the stereo input signal X, tuned under the assumption of an ideally configured system (i.e. listener in sweet spot, matched, symmetrically placed loudspeakers, etc.), the speaker matching processor <NUM> provides practical loudspeaker balancing for devices that do not provide matched speaker pairs, as is the case in the vast majority of mobile devices. The N-band parametric EQ <NUM> of the speaker matching processor <NUM> receives the left enhanced channel AL and the right enhanced channel AR, and applies an equalization to each of the channels AL and AR.

In some embodiments, the N-band EQ <NUM> provides various EQ filter types such as a low and high-shelf filter, a band-pass filter, a band-stop filter, and peak-notch filter, or low and high pass filter. If one loudspeaker in a stereo pair is angled away from the ideal listener sweet spot, for example, that loudspeaker will exhibit noticeable high-frequency attenuation from the listener sweet spot. One or more bands of the N-band EQ <NUM> can be applied on that loudspeaker channel in order to restore the high frequency energy when observed from the sweet spot (e.g., via high-shelf filter), achieving a near-match to the characteristics of the other forward facing loudspeaker. In another scenario, if both loudspeakers are front-facing but one of them has a vastly different frequency response, then EQ tuning can be applied to both left and right channels to strike a spectral balance between the two. Applying such tunings can be equivalent to "rotating" the loudspeaker of interest to match the orientation of the other, forward-facing loudspeaker. In some embodiments, the N-band EQ <NUM> includes a filter for each of n bands that are processed independently. The number of bands may vary. In some embodiments, the number of bands correspond with the subbands of the subband spatial processing.

In some embodiments, speaker asymmetry may be predefined for a particular set of speakers, with the known asymmetry being used as a basis for selecting parameters of the N-band EQ <NUM>. In another example, speaker asymmetry may be determined based on testing the speakers, such as by using test audio signals, recording the sound generated from the signals by the speakers, and analyzing the recorded sound.

The left amplifier <NUM> is coupled to the N-band EQ <NUM> to receive a left channel and the right amplifier <NUM> is coupled to the N-band EQ <NUM> to receive a right channel. The amplifiers <NUM> and <NUM> address asymmetries in loudspeaker loudness and dynamic range capabilities by adjusting the output gains on one or both channels. This is especially useful for balancing any loudness offsets in loudspeaker distances from the listening position, and for balancing unmatched loudspeaker pair that have vastly different sound pressure level (SPL) output characteristics.

The delay and gain processor <NUM> receives left and right output channels of the speaker matching processor <NUM>, and applies a time delay and gain or attenuation to one or more of the channels. To that end, the delay and gain processor <NUM> includes the left delay <NUM> that receives the left channel output from the speaker matching processor <NUM> and applies a time delay, and the left amplifier <NUM> that applies a gain or attenuation to the left channel to generate the left output channel BL. The delay and gain processor <NUM> further includes the right delay <NUM> that receives the right channel output from the speaker matching processor <NUM>, and applies a time delay, and the right amplifier <NUM> that applies a gain or attenuation to the right channel to generate the right output channel BR. As discussed above, the speaker matching processor <NUM> perceptually balances the left/right spatial image from the vantage of an ideal listener "sweet spot," focusing on providing a balanced SPL and frequency response for each driver from that position, and ignoring time-based asymmetries that exist in the actual configuration. After this speaker matching is achieved, the delay and gain processor <NUM> time aligns and further perceptually balances the spatial image from a particular listener head position, given the actual physical asymmetries in the rendering/listening system (e.g., off-center head position and/or non-equivalent loudspeaker-to-head distances).

The delay and gain values applied by the delay and gain processor <NUM> may be set to address a static system configuration, such as a mobile phone employing orthogonally oriented loudspeakers, or a listener laterally offset from the ideal listening sweet spot in front of a speaker, such as a home theater soundbar, for example.

The delay and gain values applied by the delay and gain processor <NUM> may also be dynamically adjusted based on changing spatial relationships between the listener's head and the loudspeakers, as might occur in a gaming scenario employing physical movement as a component of game play (e.g., location tracking using a depth-camera, such as for gaming or artificial reality systems ). In some embodiments, an audio processing system includes a camera, light sensor, proximity sensor, or some other suitable device that is used to determine the location of the listener's head relative to the speakers. The determined location of the user's head may be used to determine the delay and gain values of the delay and gain processor <NUM>.

Audio analysis routines can provide the appropriate inter-speaker delays and gains used to configure the b-chain processor <NUM>, resulting in a time-aligned and perceptually balanced left/right stereo image. In some embodiments, in the absence of measurable data from such analysis methods, intuitive manual user controls, or automated control via computer vision or other sensor input, can be achieved using a mapping as defined by equations <NUM> and <NUM> below: <MAT> <MAT> where delayDelta and delay are in milliseconds, and, gain is in decibels. The delay and gain column vectors assume their first component pertains to the left channel and their second to the right. Thus, delayDelta ≥ <NUM> indicates left speaker delay is greater than or equal to right speaker delay, and delayDelta < <NUM> indicates left speaker delay is less than right speaker delay.

In some embodiments, instead of applying attenuation to a channel, an equal amount of gain may be applied to the opposite channel, or a combination of gain applied to one channel and attenuation to the other channel. For example, a gain may be applied to the left channel rather than an attenuation on the left channel. For near-field listening, as occurs on mobile, desktop PC and console gaming, and home-theater scenarios, the distance deltas between a listener position and each loudspeaker are small enough, and therefore the SPL deltas between a listener position and each loudspeaker are small enough, such that any of the above mappings will serve to successfully restore the transaural spatial image while maintaining an overall acceptably loud sound stage, in comparison to an ideal listener/speaker configuration.

A result of an optimally tuned audio processing system <NUM> (also referred to as an "VS-X system") is an enhanced and spatially immersive transaural sound field, as perceived from the ideal listener "sweet spot," containing mostly spatial energy above <NUM>-<NUM>, but with enough low frequency energy rendered via the "broadband" micro-loudspeaker as to provide the perception of a full-band musical (or cinematic, etc.) listening experience.

Using VS-X, including the subband spatial processing (or other spatial enhancement processing), and assuming the appropriate amplification for both speakers, a mobile device with unmatched and non-ideally angled speakers can be transformed from a traditionally mono playback device to a perceived front-firing immersive stereo device.

<FIG> is a flow chart of a process <NUM> for virtual stereo audio reproduction (VS-X) processing of an input audio signal, in accordance with some embodiments. The process <NUM> is discussed as being performed by the audio processing system <NUM>, although other types of computing devices or circuitry may be used. The process <NUM> may include fewer or additional steps, and steps may be performed in different orders.

An audio processing system <NUM> (e.g., crossover network <NUM>) separates <NUM> an input audio signal into a low frequency signal and a high frequency signal.

The audio processing system <NUM> (e.g., high frequency processor <NUM>) applies <NUM> subband spatial processing to the high frequency signal. Applying the subband spatial processing may include gain adjusting mid subband components and side subband components of the high frequency signal to generate a high frequency output signal. The subband spatial processing enhances the spatial sense of the sound field for the high frequency signal. The subband spatial processing may further include crosstalk compensation and crosstalk cancellation.

The audio processing system <NUM> (e.g., high frequency processor <NUM>) applies <NUM> b-chain processing to the high frequency signal to adjust for an asymmetry between the speakers <NUM> and 110R. The b-chain processing corrects relative differences in delay, signal level, or frequency response between the speakers <NUM> and 110R, resulting in high frequency output signal having a restored near-ideal spatial image, as if the listener <NUM> (e.g., head position) and/or rendering system were ideally configured. In some embodiments, the audio processing system <NUM> determine asymmetries between the left speaker and the right speaker in frequency response, time alignment, and signal level for a listening position. The audio processing system <NUM> generates a left channel of the high frequency output signal and a right channel of the high frequency output signal by: applying an N-band equalization to the high frequency signal to adjust for the asymmetry in the frequency response, applying a delay to the high frequency signal to adjust for the asymmetry in the time alignment, and applying a gain to the high frequency signal to adjust for the asymmetry in the signal level.

The audio processing system <NUM> (e.g., the high frequency processor <NUM>) applies <NUM> an equalization filter to adjust a left channel of the high frequency signal relative to a right channel of the high frequency signal, and a gain to the high frequency signal to adjust the high frequency signal relative to the low frequency signal. For example, the HF EQ filter <NUM> applies to equalization filter, and the HF gain <NUM> applies the gain.

The audio processing system <NUM> (e.g., low frequency processor <NUM>) applies <NUM> a parametric band-pass filter and gain to the low frequency signal. For example, the LF boost resonator <NUM> may include the parametric band-pass filter. The filter may enhance one or more targeted portions of the mid/low frequency spectrum. The filter may also adjust the low frequency signal based on a frequency response of a "broadband" micro-loudspeaker that is to receive the processed low frequency signal. Furthermore the LF boost gain <NUM> applies a gain to the output of the filter to generate a low frequency resonator signal.

The audio processing system <NUM> (e.g., the low frequency processor <NUM>) applies <NUM> a gain to the low frequency signal to generate a low frequency passthrough signal. For example, the LF passthrough gain <NUM> attenuates the overall low frequency signal band.

The audio processing system (e.g., the low frequency processor <NUM>) combines <NUM> the low frequency resonator signal with the low frequency passthrough signal to generate a low frequency output signal.

The audio processing system <NUM> combines <NUM> the low frequency output signal to one of a left channel of the high frequency output signal or a right channel of the high frequency output signal. For example, the low frequency output signal is provided to a speaker more capable of handling low frequency reproduction in a mismatched speaker system, such as a "broad-band" micro-loudspeaker 110R of the device <NUM>. Furthermore, the low frequency output signal is not provided to another speaker that is less capable of handling the low frequency reproduction, such as the earpiece speaker <NUM> of the device <NUM>.

As such, the audio processing system generates an output signal including a left output channel and a right output channel. The left output channel includes the left channel of the high frequency output signal, and the right output channel includes the right channel of the high frequency output signal. Furthermore, one of the left output channel or the right output channel includes the low frequency output signal for the speaker more capable of handling lower frequencies in a mismatched speaker system.

The steps process <NUM> may be performed in various orders. For example, the steps <NUM>, <NUM>, and <NUM> for processing the high frequency signal may be performed in parallel with the steps <NUM>, <NUM>, and <NUM> for the processing the low frequency signal. Furthermore, the steps <NUM> and <NUM> may be performed in parallel for the low frequency signal.

<FIG> is an example of a perceived sound field of the mobile device <NUM> shown in <FIG> after VS-X processing, in accordance with some embodiments. The left output channel OL from the audio processing system <NUM> has been provided to the left speaker <NUM>L, and the right output channel OR from the audio processing system <NUM> has been provided to the right speaker <NUM>R. The resulting sound field from the mismatched left speaker <NUM>L and right speaker <NUM>R is perceived by the listener <NUM> as originating from matched, virtual speakers <NUM>L and <NUM>R.

It is noted that the systems and processes described herein may be embodied in an embedded electronic circuit or electronic system. The systems and processes also may be embodied in a computing system that includes one or more processing systems (e.g., a digital signal processor) and a memory (e.g., programmed read only memory or programmable solid state memory), or some other circuitry such as an application specific integrated circuit (ASIC) or field-programmable gate array (FPGA) circuit.

<FIG> illustrates an example of a computer system <NUM>, according to one embodiment. The audio processing system <NUM> may be implemented on the system <NUM>. Illustrated are at least one processor <NUM> coupled to a chipset <NUM>. The chipset <NUM> includes a memory controller hub <NUM> and an input/output (I/O) controller hub <NUM>. A memory <NUM> and a graphics adapter <NUM> are coupled to the memory controller hub <NUM>, and a display device <NUM> is coupled to the graphics adapter <NUM>. A storage device <NUM>, keyboard <NUM>, pointing device <NUM>, and network adapter <NUM> are coupled to the I/O controller hub <NUM>. Other embodiments of the computer <NUM> have different architectures. For example, the memory <NUM> is directly coupled to the processor <NUM> in some embodiments.

The storage device <NUM> includes one or more non-transitory computer-readable storage media such as a hard drive, compact disk read-only memory (CD-ROM), DVD, or a solid-state memory device. The memory <NUM> holds program code (or software) and data used by the processor <NUM>. The program code may be one or more instructions executable by athe processor <NUM>. For example, the memory <NUM> may store instructions that when executed by the processor <NUM> causes or configures the processor <NUM> to perform the functionality discussed herein, such as the process <NUM>. The pointing device <NUM> is used in combination with the keyboard <NUM> to input data into the computer system <NUM>. The graphics adapter <NUM> displays images and other information on the display device <NUM>. In some embodiments, the display device <NUM> includes a touch screen capability for receiving user input and selections. The network adapter <NUM> couples the computer system <NUM> to a network. Some embodiments of the computer <NUM> have different and/or other components than those shown in <FIG>. For example, the computer system <NUM> may be a server that lacks a display device, keyboard, and other components, or may use other types of input devices.

The disclosed configuration may include a number of benefits and/or advantages. For example, an input signal can be output to unmatched loudspeakers while preserving or enhancing a spatial sense of the sound field. A high quality listening experience can be achieved even when the speakers are unmatched or when the listener is not in an ideal listening position relative to the speakers.

Claim 1:
A system (<NUM>) for processing an input audio signal including a left input channel and a right input channel, the system comprising:
a crossover network (<NUM>) configured to separate (<NUM>) the input audio signal into a low frequency signal (<NUM>) and a high frequency signal (<NUM>);
a high frequency processor (<NUM>) configured to apply (<NUM>) a b-chain processing to the high frequency signal (<NUM>) to generate a high frequency output signal, the b-chain processing comprising adjusting for an asymmetry between a left speaker (<NUM>) and a right speaker (110R) in at least one of a frequency response, a time alignment, or a signal level;
a low frequency processor (<NUM>) configured to:
apply (<NUM>) a parametric band-pass filter and a first gain to the low frequency signal (<NUM>) to generate a low frequency resonator signal,
apply (<NUM>) a second gain to the low frequency signal to generate a low frequency passthrough signal, and
generate (<NUM>) a low frequency output signal by combining the low frequency resonator signal with the low frequency passthrough signal; and
a combiner (<NUM>) configured to generate an output signal including a left channel of the high frequency output signal for the left speaker and a right channel of the high frequency output signal for the right speaker, wherein the combiner is further configured to combine (<NUM>) the low frequency output signal with one of the left channel of the high frequency output signal for the left speaker or the right channel of the high frequency output signal for the right speaker.