Techniques for distortion reducing multi-band compressor with timbre preservation

Patent metadata

Field	Value
Publication number	US-2018152166-A1
Application number	US-201815873814-A
Country	US
Kind code	A1
Filing date	Jan 17, 2018
Priority date	Mar 18, 2010
Publication date	May 31, 2018
Grant date	—

Abstract

Distortion reducing multi-band compressor with timbre preservation is provided. Timbre preservation is achieved by determining a time-varying threshold in each of a plurality frequency bands as a function of a respective fixed threshold for the frequency band and, at least in part, an audio signal level and a fixed threshold outside such frequency band. If a particular frequency band receives significant gain reduction due to being above or approaching its fixed threshold, then a time-varying threshold of one or more other frequency bands are also decreased to receive some gain reduction. In a specific embodiment, time-varying thresholds can be computed from an average difference of the audio input signal in each frequency band and its respective fixed threshold.

First claim

What is claimed is:

1 . A method for audio presentation, the method comprising:
splitting an audio signal into a plurality of frequency bands; determining a time-varying threshold for a first frequency band of the plurality of frequency bands, the time-varying threshold determined from a level of the audio signal and a fixed signal level threshold corresponding to each of a plurality of neighboring frequency bands; providing the time-varying threshold to a compression function element dedicated to the first frequency band; and audibly presenting an audio signal outputted from the compression function element.

2 . The method of claim 1 , wherein the time-varying threshold is determined from the level of the audio signal and a fixed signal level threshold corresponding to each frequency band of the plurality of frequency bands.

3 . The method of claim 1 , wherein the time-varying threshold is determined from the level of the audio signal and a fixed signal level threshold corresponding to each frequency band of some, but not all, of the plurality of frequency bands.

4 . The method of claim 1 , wherein the time-varying threshold is not based on isolated frequency bands of the plurality of frequency bands.

5 . The method of claim 4 , wherein the isolated frequency bands include the lowest-frequency bands of the plurality of frequency bands.

6 . The method of claim 4 , wherein the isolated frequency bands include frequency bands having lower fixed thresholds relative to the fixed thresholds of other frequency bands of the plurality of frequency bands.

7 . The method of claim 1 , wherein determining the time-varying threshold involves applying a frequency-dependent weighting function.

8 . The method of claim 7 , wherein the frequency-dependent weighting function applies a lower weight to relatively lower-frequency bands.

9 . The method of claim 1 , wherein the time-varying threshold is based, at least in part, on an average difference between an audio input signal level for each frequency band of the plurality of frequency bands and a fixed signal level of each frequency band of the plurality of frequency bands.

10 . The method of claim 1 , wherein the time-varying threshold is based, at least in part, on an average difference between an audio input signal level for each frequency band of the plurality of neighboring frequency bands and a fixed signal level of each frequency band of the plurality of neighboring frequency bands.

11 . The method of claim 1 , further comprising determining a gain for each frequency band of the plurality of frequency bands.

12 . The method of claim 11 , further comprising:
determining that a gain reduction should be applied to a gain of the first frequency band of the plurality of neighboring frequency bands; and decreasing a time-varying threshold of one or more neighboring frequency bands of the plurality of neighboring frequency bands based, at least in part, on the gain reduction.

13 . The method of claim 11 , further comprising:
applying a first smoothing function for smoothing levels of audio input signals used for determining the gains; and applying a second smoothing function for smoothing levels of audio input signals used for determining the time-varying threshold, wherein the second smoothing function includes longer time constants than first smoothing function.

14 . The method of claim 11 , further comprising:
determining a smoothed energy signal for each frequency band of the plurality of frequency bands; determining a difference between the smoothed energy signal and a fixed threshold for each frequency band of the plurality of frequency bands; and determining a minimum difference over all bands of the plurality of frequency bands.

15 . The method of claim 14 , further comprising determining a weighted average of the differences, wherein the time-varying threshold is based, at least in part, on the weighted average.

16 . The method of claim 11 , further comprising:
determining a smoothed energy signal for each frequency band of the plurality of frequency bands; determining a difference between the smoothed energy signal and a fixed threshold for each frequency band of the plurality of frequency bands; and determining a maximum difference over all bands of the plurality of frequency bands.

17 . The method of claim 16 , further comprising determining the time-varying threshold based, at least in part, on the maximum difference.

18 . An apparatus, comprising:
a multi-band filterbank configured for splitting an audio signal into a plurality of frequency bands; a timbre preservation element configured for determining a time-varying threshold for a first frequency band of the plurality of frequency bands, the time-varying threshold determined from a level of the audio signal and a fixed signal level threshold corresponding to each of a plurality of neighboring frequency bands; and a compression function element configured for receiving the time-varying threshold from the timbre preservation element and for applying an amount of compression for the first frequency band based, at least in part, on the time-varying threshold.

19 . The apparatus of claim 18 , further comprising an audio transducer, wherein the apparatus is configured for audibly presenting an audio signal outputted from the compression function element via the audio transducer.

20 . A non-transitory storage medium having instructions stored thereon for controlling one or more devices to perform a method for audio presentation, the method comprising:
splitting an audio signal into a plurality of frequency bands; determining a time-varying threshold for a first frequency band of the plurality of frequency bands, the time-varying threshold determined from a level of the audio signal and a fixed signal level threshold corresponding to each of a plurality of neighboring frequency bands; providing the time-varying threshold to a compression function element dedicated to the first frequency band; and audibly presenting an audio signal outputted from the compression function element.

Assignees

• Dolby Laboratories Licensing Corp

Inventors

• Seefeldt Alan Jeffrey

Classifications

• H03G9/18

  for tone control and volume expansion or compression · CPC title

• H03G9/025

  frequency-dependent volume compression or expansion, e.g. multiple-band systems (H03G9/10, H03G9/18 take precedence) · CPC title

• H03G9/10 Primary

  for tone control and volume expansion or compression · CPC title

• H03G9/005 Primary

  of digital or coded signals · CPC title

• H04R3/04

  for correcting frequency response · CPC title