Temporal offset estimation
A method of non-causally shifting a channel includes estimating comparison values at an encoder. Each comparison value is indicative of an amount of temporal mismatch between a previously captured reference channel and a corresponding previously captured target channel. The method also includes smoothing the comparison values to generate smoothed comparison values based on historical comparison value data and a smoothing parameter. The method further includes estimating a tentative shift value based on the smoothed comparison values. The method also includes non-causally shifting a target channel by a non-causal shift value to generate an adjusted target channel that is temporally aligned with a reference channel. The non-causal shift value is based on the tentative shift value. The method further includes generating, based on reference channel and the adjusted target channel, at least one of a mid-band channel or a side-band channel.
1. A method comprising:
estimating comparison values at an encoder, each comparison value indicative of an amount of temporal mismatch between a previously captured reference channel and a corresponding previously captured target channel;
smoothing the comparison values to generate smoothed comparison values based on historical comparison value data and a smoothing parameter, the smoothing parameter having a value that is based on at least one short-term signal level indicator of input channels and at least one long-term signal level indicator of the input channels;
estimating a tentative shift value based on the smoothed comparison values;
non-causally shifting a particular target channel by a non-causal shift value to generate an adjusted particular target channel that is temporally aligned with a particular reference channel, the non-causal shift value based on the tentative shift value; and
generating at least one of a mid-band channel or a side-band channel based on the particular reference channel and the adjusted particular target channel.
2. The method of claim 1 , wherein the smoothing parameter is adaptive.
3. The method of claim 1 , further comprising adapting the smoothing parameter based on a variation in short-term comparison values relative to long-term comparison values.
4. The method of claim 1 , wherein the value of the smoothing parameter is reduced if the short-term signal level indicators are greater than the long-term signal level indicators.
5. The method of claim 1 , wherein the value of the smoothing parameter is adjusted based on a variation in short-term smoothed comparison values relative to long-term smoothed comparison values.
6. The method of claim 5 , wherein the value of the smoothing parameter is increased if the variation exceeds a threshold.
7. The method of claim 1 , wherein the comparison values comprise cross-correlation values of down-sampled reference channels and corresponding down-sampled target channels.
8. The method of claim 1 , further comprising adjusting a range of the comparison values, wherein the tentative shift value is associated with a comparison value in the range of the comparison values having a highest cross-correlation.
9. The method of claim 8 , wherein adjusting the range comprises:
determining whether particular comparison values at a boundary of the range are monotonously increasing; and
expanding the boundary in response to a determination that the particular comparison values at the boundary are monotonously increasing.
10. The method of claim 9 , wherein the boundary includes a left boundary or a right boundary.
11. The method of claim 1 , wherein a reference frame of the particular reference channel and a target frame of the particular target channel are one of voiced frames, transition frames, or unvoiced frames.
12. The method of claim 1 , wherein estimating the comparison values, smoothing the comparison values, estimating the tentative shift value, and non-causally shifting the target channel are performed at a mobile device.
13. The method of claim 1 , wherein estimating the comparison values, smoothing the comparison values, estimating the tentative shift value, and non-causally shifting the target channel are performed at a base station.
14. The method of claim 1 , wherein the input channels correspond to previously captured reference channels and corresponding previously captured target channels.
15. The method of claim 1 , wherein the short-term signal level indicator is based on a sum of absolute values of the input channels.
16. The method of claim 1 , wherein the short-term signal level indicator is based on a sum of squares of the input channels.
17. The method of claim 1 , wherein the short-term signal level indicator is based on a sum of absolute values of down-sampled channels associated with the input channels.
18. An apparatus comprising:
a first microphone configured to capture a particular reference channel;
a second microphone configured to capture a particular target channel; and
an encoder configured to:
estimate comparison values, each comparison value indicative of an amount of temporal mismatch between a previously captured reference channel and a corresponding previously captured target channel;
smooth the comparison values to generate smoothed comparison values based on historical comparison value data and a smoothing parameter, the smoothing parameter having a value that is based on at least one short-term signal level indicator of input channels and at least one long-term signal level indicator of the input channels;
estimate a tentative shift value based on the smoothed comparison values;
non-causally shift the particular target channel by a non-causal shift value to generate an adjusted particular target channel that is temporally aligned with the particular reference channel, the non-causal shift value based on the tentative shift value; and
generate at least one of a mid-band channel or a side-band channel based on the particular reference channel and the adjusted particular target channel.
19. The apparatus of claim 18 , wherein the smoothing parameter is adaptive.
20. The apparatus of claim 18 , wherein the encoder is further configured to adapt the smoothing parameter based on a correlation of short-term comparison values to long-term comparison values.
21. The apparatus of claim 18 , wherein the encoder is further configured to reduce the value of the smoothing parameter if the short-term signal level indicators are greater than the long-term signal level indicators.
22. The apparatus of claim 18 , wherein the encoder is further configured to adjust the value of the smoothing parameter based on a correlation of short-term smoothed comparison values to long-term smoothed comparison values.
23. The apparatus of claim 22 , wherein the encoder is further configured to increase the value of the smoothing parameter if the correlation exceeds a threshold.
24. The apparatus of claim 18 , wherein the comparison values are cross-correlation values of down-sampled reference channels and corresponding down-sampled target channels.
25. The apparatus of claim 18 , wherein the encoder is further configured to adjust adjusting a range of the comparison values, wherein the tentative shift value is associated with a comparison value in the range of the comparison values having a highest cross-correlation.
26. The apparatus of claim 18 , wherein the encoder is integrated into a mobile device.
27. The apparatus of claim 18 , wherein the encoder is integrated into a base station.
28. A non-transitory computer-readable medium comprising instructions that, when executed by an encoder, cause the encoder to perform operations comprising:
estimating comparison values, each comparison value indicative of an amount of temporal mismatch between a previously captured reference channel and a corresponding previously captured target channel;
smoothing the comparison values to generate smoothed comparison values based on historical comparison value data and a smoothing parameter, the smoothing parameter having a value that is based on at least one short-term signal level indicator of input channels and at least one long-term signal level indicator of the input channels;
estimating a tentative shift value based on the smoothed comparison values;
non-causally shifting a particular target channel by a non-causal shift value to generate an adjusted particular target channel that is temporally aligned with a particular reference channel, the non-causal shift value based on the tentative shift value; and
generating at least one of a mid-band channel or a side-band channel based on the particular reference channel and the adjusted particular target channel.
29. The non-transitory computer-readable medium of claim 28 , wherein the smoothing parameter is adaptive.
30. The non-transitory computer-readable medium of claim 28 , wherein the operations further comprise adapting the smoothing parameter based on a correlation of short-term comparison values to long-term comparison values.
31. An apparatus comprising:
means for estimating comparison values, each comparison value indicative of an amount of temporal mismatch between a previously captured reference channel and a corresponding previously captured target channel;
means for smoothing the comparison values to generate smoothed comparison values based on historical comparison value data and a smoothing parameter, the smoothing parameter having a value that is based on at least one short-term signal level indicator of input channels and at least one long-term signal level indicator of the input channels;
means for estimating a tentative shift value based on the smoothed comparison values;
means for non-causally shifting a particular target channel by a non-causal shift value to generate an adjusted particular target channel that is temporally aligned with a particular reference channel, the non-causal shift value based on the tentative shift value; and
means for generating at least one of a mid-band channel or a side-band channel based on the particular reference channel and the adjusted particular target channel.
32. The apparatus of claim 31 , wherein the smoothing parameter is adaptive.
33. The apparatus of claim 31 , wherein the means for estimating the comparison values, the means for smoothing the comparison values, the means for estimating the tentative shift value, and the means for non-causally shifting the target channel are integrated into a mobile device.
34. The apparatus of claim 31 , wherein the means for estimating the comparison values, the means for smoothing the comparison values, the means for estimating the tentative shift value, and the means for non-causally shifting the target channel are integrated into a base station.