Comfort Noise Generation

Patent metadata

Field	Value
Publication number	US-2016133264-A1
Application number	US-201514934658-A
Country	US
Kind code	A1
Filing date	Nov 6, 2015
Priority date	Nov 6, 2014
Publication date	May 12, 2016
Grant date	—

Abstract

A system for generating comfort noise for a stream of frames carrying an audio signal includes frame characterizing logic configured to generate a set of filter parameters characterising the frequency content of a frame; an analysis filter adapted using the filter parameters and configured to filter the frame so as to generate residual samples; an analysis controller configured to cause the residual samples to be stored in a store responsive to receiving an indication that the frame does not comprise speech; and a synthesis controller operable to select stored residual samples from the store and cause a synthesis filter, inverse to the analysis filter and adapted using filter parameters generated by the frame characterizing logic for one or more frames not comprising speech, to filter the selected residual samples so as to generate a frame of comfort noise.

First claim

1 . A system for generating comfort noise for a stream of frames carrying an audio signal, the system comprising:
frame characterizing logic configured to generate a set of filter parameters characterizing the frequency content of a frame; an analysis filter adapted using the filter parameters and configured to filter the frame so as to generate residual samples; an analysis controller configured to cause the residual samples to be stored in a store responsive to receiving an indication that the frame does not comprise speech;
and
a synthesis controller operable to select stored residual samples from the store and cause a synthesis filter, inverse to the analysis filter and adapted using filter parameters generated by the frame characterising logic for one or more frames not comprising speech, to filter the selected residual samples so as to generate a frame of comfort noise.

2 . The system as claimed in claim 1 , wherein the analysis controller is further configured to cause the residual samples to be stored at the store responsive to receiving at least a predetermined number of the indications in respect of consecutive frames of the stream indicating that those respective frames do not comprise speech.

3 . The system as claimed in claim 2 , wherein the analysis controller is further configured to store residual samples generated for one or more preceding frames of the consecutive frames of the stream in respect of which indications are received.

4 . The system as claimed in claim 1 , wherein the frame characterizing logic is further configured to generate the set of filter parameters using linear predictive coding.

5 . The system as claimed in claim 4 , wherein the analysis filter comprises an inverse LPC filter and wherein the synthesis filter comprises an LPC filter.

6 . The system as claimed in claim 1 , wherein the frame characterizing logic is further configured to, responsive to the indication that the frame does not comprise speech, store the set of filter parameters at a parameter buffer and wherein the synthesis controller is further configured to select a set of filter parameters from the parameter buffer for use at the synthesis filter.

7 . The system as claimed in claim 6 , wherein the synthesis controller is further configured to select the set of filter parameters at random from the parameter buffer.

8 . The system as claimed in claim 1 , wherein the analysis controller is further configured to cause the frame characterizing logic to generate the set of filter parameters for the frame and the analysis filter to filter the frame in response to the indication that the frame does not comprise speech.

9 . The system as claimed in claim 1 , wherein the store comprises an auxiliary buffer and a residue buffer, wherein the analysis controller is further configured to cause the residual samples generated at the analysis filter to be stored at the auxiliary buffer and to copy one or more residual samples from the auxiliary buffer to the residue buffer when the auxiliary buffer holds a predefined number of residual samples, and wherein the synthesis controller is further configured to perform the selection of the stored residual samples from the residue buffer.

10 . The system as claimed in claim 9 , wherein the analysis controller is further configured to copy all of the residual samples stored at the auxiliary buffer into the residue buffer when the auxiliary buffer is full and to flush the auxiliary buffer.

11 . The system as claimed in claim 9 , wherein the analysis controller is further configured to flush the auxiliary buffer responsive to receiving an indication that the frame of the stream comprises speech.

12 . The system as claimed in claim 1 , wherein the synthesis controller is further configured to select stored residual samples at random from the store sufficient to generate the frame of comfort noise.

13 . The system as claimed in claim 1 , further comprising a voice activity detector for identifying speech in the frame and for providing said indication to the analysis controller.

14 . The system as claimed in claim 13 , wherein the system is implemented at a communication device having a microphone for capturing near-end speech and a speaker for outputting far-end speech received from another communication device, wherein the audio signal represents an output of the microphone, and wherein the voice activity detector is configured to provide the indication to the analysis controller responsive to determining that the frame does not include near-end speech.

15 . The system as claimed in claim 1 , wherein the indication that the frame does not comprise speech comprises an indication that the frame is a noise frame which does not comprise near-end speech or an echo of far-end speech.

16 . The system as claimed in claim 1 , wherein the synthesis controller is activated independently from the analysis controller in respect of a frame of the stream which is to be replaced with a frame of comfort noise.

17 . The system as claimed in claim 1 , wherein the synthesis controller is further configured to, in response to a request for a frame of comfort noise, select stored residual samples and cause the synthesis filter to filter the selected residual samples so as to generate a frame of comfort noise.

18 . The system as claimed in claim 1 , wherein the frame characterizing logic, the analysis filter, and the synthesis filter comprise part of one processing path of a plurality of processing paths, wherein each processing path of the plurality of processing paths comprises a frame characterizing logic, an analysis filter, and a synthesis filter, and wherein each processing path is arranged to independently generate comfort noise for a respective one of a plurality of frequency sub-bands of the audio signal comprised in the stream of frames, wherein the system further comprises an analysis filter bank arranged to decompose the frame into the plurality of frequency sub-bands and a synthesis filter bank arranged to combine the comfort noise generated for each frequency sub-band into said frame of comfort noise.

19 . A method for generating comfort noise for a stream of frames carrying an audio signal, the method comprising the steps of:
receiving a frame; generating a set of filter parameters characterising the frequency content of the frame; adapting an analysis filter using the filter parameters; filtering the frame at the analysis filter so as to generate residual samples; in response to determining that the frame does not comprise speech, causing the residual samples to be stored in a store;
and, in response to receiving a request for comfort noise in respect of the frame:
selecting stored residual samples from the store;
adapting a synthesis filter using filter parameters generated for one or more frames not comprising speech; and
filtering the selected residual samples at the synthesis filter so as to generate a frame of comfort noise.

20 . A non-transitory machine readable storage medium having encoded thereon machine readable code that, when executed at a computer system, causes the computer system to perform a method of generating comfort noise for a stream of frames carrying an audio signal, the method comprising the steps of:
receiving a frame; generating a set of filter parameters characterising the frequency content of the frame; adapting an analysis filter using the filter parameters; filtering the frame at the analysis filter so as to generate residua

Assignees

• Imagination Tech Ltd

Inventors

• Mani Senthil Kumar
• Akella Srinivas

Classifications

• G10L19/012 Primary

  Comfort noise or silence coding · CPC title

• G10L25/78 Primary

  Detection of presence or absence of voice signals (switching of direction of transmission by voice frequency in two-way loud-speaking telephone systems H04M9/10) · CPC title

• G10L19/06

  Determination or coding of the spectral characteristics, e.g. of the short-term prediction coefficients · CPC title

• H04M9/082

  using echo cancellers (echo cancellers per se H04B3/23) · CPC title

• H04M3/002

  Applications of echo suppressors or cancellers in telephonic connections (in two-way loud-speaking telephone systems H04M9/08, echo suppressors or cancellers per se H04B3/20) · CPC title