Non-causal postfilter

• US 8,620,645 B2
• Filed: 12/14/2007
• Issued: 12/31/2013
• Est. Priority Date: 03/02/2007
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Bruhn, Stefan
• Primary Examiner(s): COLUCCI, MICHAEL C
• Application Number:
  US12/529,682
• Publication Number:
  US 20100063805A1
• Time in Patent Office: 2,209 Days
• Field of Search: 704/211, 704/230, 704/270, 704/228, 704/223, 704/221, 704/219, 704/214, 704/200.1, 370/516, 370/503, 370/352, 375/285, 375/240.5
• US Class Current: 704/207
• CPC Class Codes: G10L 19/26 Pre-filtering or post-filtering

Abstract

A decoder arrangement comprising a receiver input for parameters of frame-based coded signals and a decoder arranged to provide frames of decoded audio signals based on the parameters. The receiver input and/or the decoder is arranged to establish a time difference between the occasion when parameters of a first frame is available at the receiver input and the occasion when a decoded audio signal of the first frame is available at an output of the decoder, which time difference corresponds to at least one frame. A postfilter is connected to the output of the decoder and to the receiver input. The postfilter is arranged to provide a filtering of the frames of decoded audio signals into an output signal in response to parameters of a respective subsequent frame.

Claims

1. A decoder arrangement, comprising:

a receiver input for parameters of frame-based coded signals;

a decoder connected to said receiver input, arranged to provide frames of decoded audio signals based on said parameters;

a postfilter connected to an output of said decoder and arranged to provide an output signal based on said frames of decoded audio signals;

wherein at least one of said receiver input and said decoder is arranged to establish a time difference between the occasion when parameters of a first frame (x(n)) is available at said receiver input and the occasion when a decoded audio signal of said first frame (y(n)) is available at said output of said decoder, which time difference corresponds to at least one frame;

the postfilter further arranged to receive said first frame of the decoded audio signals (y(n)) essentially simultaneously as the parameter of a respective subsequent frame (x(n+1));

wherein said postfilter is connected to said receiver input; and

,

wherein said postfilter is arranged to provide a filtering of said first frame of the decoded audio signals (y(n)) into an output signal (y_out(n)) using said parameter of the respective subsequent frame (x(n+1)).

2. The decoder arrangement according to claim 1, wherein said receiver input comprises a storage for parameters of at least two consecutive frames, wherein said decoder is provided with parameters of a first frame and said postfilter has access to parameters of a subsequent second frame.

3. The decoder arrangement according to claim 1, wherein said decoder comprises means for delaying said frames of decoded audio signals before being outputted to said postfilter.

4. The decoder arrangement according to claim 1, wherein said postfilter comprises a pitch postfilter, wherein a pitch parameter used in said pitch postfilter is based on a pitch parameter of said subsequent frame.

5. The decoder arrangement according to claim 4, wherein said pitch postfilter of said postfilter is arranged for determining, for a following subframe, a value of a time index reduced by a pitch value for said following subframe, and taking, if said determined value is larger or equal to a present time index, said pitch value for said following subframe as pitch lead parameter for said present frame.

6. The decoder arrangement according to claim 4, further comprising an audio characteristics detector, an output of which is connected to said postfilter;

wherein said postfilter is arranged to adapt the degree in which said pitch parameter used in said pitch postfilter is based on said pitch parameter of said subsequent frame dependent on a measure of a significance of change in audio characteristics between a present frame and at least one of a previous frame and a subsequent frame.

7. The decoder arrangement according to claim 6, wherein said audio characteristics detector is at least one of a voice activity detector and a voicing detector, wherein said postfilter is arranged to base said pitch parameter used in said pitch postfilter on said pitch parameter of said subsequent frame in case of a detected voiced speech onset.

8. The decoder arrangement according to claim 1, wherein said postfilter is arranged to have access also to a decoded signal of said subsequent frame.

9. The decoder arrangement according to claim 1, wherein said decoder is a scalable decoder or a part of a scalable decoder, wherein a secondary decoder of said scalable decoder has a higher delay than a primary decoder of said scalable decoder.

10. A decoder arrangement comprising a scalable decoder and at least two decoder arrangements according to claim 7.

11. A decoding method, comprising the steps of:

receiving parameters of frame-based coded signals;

decoding said parameters into frames of decoded audio signals;

wherein at least one of said step of receiving and said step of decoding causes a time difference between the occasion when parameters of a first frame (x(n)) is available after reception and the occasion when a decoded audio signal of the first frame (y(n)) is available after decoding, which time difference corresponds to at least one frame;

receiving, at a postfilter, said first frame of the decoded audio signals (y(n)) essentially simultaneously as the parameter of a respective subsequent frame (x(n+1));

postfiltering said first frame of the decoded audio signals (y(n)) into an output signal (y_out(n)) using said parameter of the respective subsequent frame (x(n+1)); and

,

outputting said output signal.

12. The decoding method according to claim 11, further comprising the step of storing parameters of at least two consecutive frames at each instant, wherein said step of decoding is performed with parameters of a first frame and said postfiltering is performed with access to parameters of a subsequent second frame.

13. The decoding method according to claim 11, further comprising the step of delaying said frames of decoded audio signals before performing said step of postfiltering.

14. The decoding method according to claim 11, wherein said step of postfiltering comprises pitch postfiltering, wherein a pitch parameter used in said pitch postfiltering is based on a pitch parameter of said subsequent frame.

15. The decoding method according to claim 14, wherein said pitch postfiltering in said step of postfiltering comprises:

determining, for a following subframe, a value of a time index reduced by a pitch value for said following subframe; and

,

taking, if said determined value is larger or equal to a present time index, said pitch value for said following subframe as pitch lead parameter for said present frame.

16. The decoding method according to claim 14, further comprising the step of detecting audio characteristics of said frame-based coded signals;

wherein said step of postfiltering adapts the degree in which said pitch parameter is based on said pitch parameter of said subsequent frame dependent on a measure of a significance of change in audio characteristics between a present frame and at least one of a previous frame and a subsequent frame.

17. The decoding method according to claim 16, wherein said step of detecting comprises detecting of at least one of voice activity and voicing and wherein said step of postfiltering bases said pitch parameter on said pitch parameter of said subsequent frame only in case of a detected voiced speech onset.

18. The decoding method according to claim 11, wherein said step of postfiltering is performed also in response to a decoded signal of said respective subsequent frame.

19. The decoding method according to claim 11, wherein said step of decoding comprises decoding in a scalable decoder wherein a secondary decoding involves a higher delay than a primary decoding.

20. A decoding method comprising at least two decoding methods according to claim 19.