Binaural synthesis
Embodiments relate to obtaining filter coefficients for a binaural synthesis filter; and applying a compensation filter to reduce artifacts resulting from the binaural synthesis filter; wherein the filter coefficients and compensation filter are configured to be used to obtain binaural audio output from a monaural audio input. The filter coefficients and compensation filter may be applied to the monaural audio input to obtain the binaural audio output. The compensation filter may comprise a timbre compensation filter.
1. A method comprising:
obtaining one or more sets of initial filter coefficients, each set of initial filter coefficients corresponding to an angular position defined by an azimuth angle and an elevation angle; and
adjusting each set of initial filter coefficients with a timbre compensation filter to reduce artefacts associated with a binaural audio output resulting from a binaural synthesis filter;
wherein the adjusted sets of filter coefficients are provided to the binaural synthesis filter to synthesise the binaural audio output based on a monaural input, wherein synthesising the binaural audio output comprises convolving at least one of the adjusted sets of filter coefficients with the monaural audio input.
2. The method of claim 1 , wherein the artefacts comprise a reduction in quality of the binaural audio output.
3. The method of claim 1 , wherein the artefacts comprise at least one of: a change in amplitude of the binaural audio output, a change in delay of the binaural audio output, and a change in frequency of the binaural audio output.
4. The method of claim 1 , wherein the binaural audio output occupies a frequency range, and wherein the artefacts are present in a sub-region of the frequency range.
5. The method of claim 4 , wherein the sub-region comprises audible frequencies of human voice.
6. The method of claim 1 , wherein adjusting each set of initial filter coefficients with the timbre compensation filter comprises applying the timbre compensation filter to each set of filter coefficients to obtain the adjusted filter coefficients.
7. The method of claim 1 , further comprising:
receiving the monaural audio input, the monaural audio input corresponding to and audio source having an associated position; and
synthesising binaural audio output from the monaural audio input using the binaural synthesis filter, wherein the synthesising depends on the position associated with the audio source.
8. The method of claim 1 , wherein each set of filter coefficients is adjusted with the timbre compensation filter such that the binaural audio output synthesised using the adjusted coefficients has a different timbre from binaural audio output synthesised using the initial filter coefficients to reduce an effect of the artefacts.
9. The method of claim 8 , wherein the synthesising is performed in real time, the position the audio source changes with time, and the synthesising of the binaural audio output is updated with the changing position of the audio source.
10. The method of claim 1 , further comprising generating the timbre compensation filter from one of the sets of initial filter coefficients.
11. The method of claim 10 , wherein generating the timbre compensation filter from one of the sets of initial filter coefficients comprises:
applying a filter defined by one of the sets of initial filter coefficients to a test audio input to obtain an impulse response;
obtaining a transfer function by applying a Fourier transfer to the impulse response; and
generating the timbre compensation filter from the transfer function.
12. The method of claim 11 , wherein generating the timbre compensation filter from the transfer function comprises inverting the transfer function.
13. The method of claim 12 , wherein generating the timbre compensation filter further comprises reducing an effect of the timbre compensation filter at low frequencies, and wherein the low frequencies comprise frequencies below 400 Hz.
14. The method of claim 10 , wherein generating the timbre compensation filter comprises generating the timbre compensation filter for each of a plurality of sampling rates.
15. The method of claim 10 , wherein generating the timbre compensation filter comprises truncating the timbre compensation filter to an order no higher than an order of the binaural synthesis filter.
16. The method of claim 10 , wherein the test audio input comprises an audio input having a known frequency profile, and wherein the generating of the timbre compensation filter depends on a difference between a frequency profile of the binaural audio output and the known frequency profile of the test audio input.
17. The method of claim 1 , wherein the binaural synthesis filter comprises a pinna model filter.
18. The method of claim 17 , wherein synthesising the binaural audio output further comprises:
applying an interaural time delay; and
applying a head shadow filter.
19. The method of claim 18 , further comprising determining values for the interaural time delay using the equation:
T
(
θ
,
ϕ
)
=
{
-
a
c
*
cos
(
θ
)
*
cos
(
ϕ
)
,
0
≤
θ
<
π
2
a
c
*
(
θ
-
π
2
)
*
cos
(
ϕ
)
,
π
2
≤
θ
≤
π
wherein T (θ,ϕ) is the interaural time delay, a is an average head size, c is the speed of sound, θ is an azimuth angle in radians and ϕ is an elevation angle in radians.
20. The method of claim 18 , further comprising determining values for the head shadow filter using the equation:
H
(
ω
,
θ
)
=
(
1
+
j
(
α
*
ω
)
(
2
ω
0
)
)
(
1
+
j
ω
2
ω
0
)
,
0
≤
α
(
θ
)
≤
2
wherein H(ω,θ) is a head shadow filter value, θ is an azimuth angle in degrees, ω is a radian frequency, a is an average head size, c is the speed of sound, ω 0 =c/a, and
α
(
θ
)
=
1.05
+
0.95
*
cos
(
θ
*
π
180
)
.
21. The method of claim 1 , wherein adjusting each set of initial filter coefficients with the timbre compensation filter comprises, for each angular position, applying the timbre compensation filter to the set of filter coefficients for the angular position—to obtain adjusted filter coefficients for the angular position.
22. A method comprising:
obtaining a set of initial filter coefficients for a binaural synthesis filter, the set of initial filter coefficients corresponding to an angular position defined by an azimuth angle and an elevation angle; and
generating a timbre compensation filter from the set of initial filter coefficients,
wherein the timbre compensation filter is used to adjust the set of initial filter coefficients to reduce artefacts associated with a binaural audio output resulting from the binaural synthesis filter, and
wherein the adjusted set of filter coefficients is provided to the binaural synthesis filter to synthesise the binaural audio output based on a monaural audio input, wherein synthesising of the binaural audio output comprises convolving the adjusted set of filter coefficients with the monaural audio input.
23. A method comprising:
receiving a monaural audio signal corresponding to an audio source, the audio source having an associated position; and
synthesising a binaural audio output from the monaural audio signal using a binaural synthesis filter, wherein the synthesising depends on the position associated with the audio source,
wherein the binaural synthesis filter uses adjusted filter coefficients that were adjusted using a timbre compensation filter to reduce artefacts associated with the synthesised binaural audio output.
24. An apparatus comprising:
a means for obtaining one or more sets of initial filter coefficients, each set of initial filter coefficients corresponding to an angular position defined by an azimuth angle and an elevation angle; and
a means for adjusting each set of initial filter coefficients with a timbre compensation filter to reduce artefacts associated with a binaural audio output resulting from a binaural synthesis filter;
wherein the adjusted sets of filter coefficients are provided to the binaural synthesis filter to synthesise the binaural audio output based on a monaural audio input, wherein synthesising the binaural audio output comprises convolving at least one of the adjusted sets of filter coefficients with the monaural audio input.
25. A non-transitory computer readable storage medium storing instructions, the instructions when executed by a processor cause the processor to:
obtain one or more sets of initial filter coefficients, each set of initial filter coefficients corresponding to an angular position defined by an azimuth angle and an elevation angle; and
adjust each set of initial filter coefficients with a timbre compensation filter to reduce artefacts associated with a binaural audio output resulting from a binaural synthesis filter;
wherein the adjusted sets of filter coefficients are provided to the binaural synthesis filter to synthesise the binaural audio output based on a monaural audio input, wherein synthesising the binaural audio output comprises convolving at least one of the adjusted sets of filter coefficients with the monaural audio input.