Device for Perceptual Weighting in Audio Encoding/Decoding

• US 20090076829A1
• Filed: 02/07/2007
• Published: 03/19/2009
• Est. Priority Date: 02/14/2006
• Status: Active Grant

• Current Assignee: Orange S.A.
• Original Assignee: Orange S.A.
• Inventors: Ragot, Stephane, Trilling, Romain
• Granted Patent: US 8,260,620 B2
• Time in Patent Office: Days
• US Class Current: 704/500
• CPC Class Codes: G10L 19/0208 Subband vocoders
• CPC Class Codes: G10L 19/24 Variable rate codecs, e.g. for generating different qualities using a scalable representation such as hierarchical encoding or layered encoding

Abstract

A hierarchical audio coder for use in a frequency band divided into adjacent first and second sub-bands, said coder comprising: a core coder (305) for coding an original signal in the first sub-band of said frequency band; a stage (306) for calculating a residual signal (e) from said original signal and the signal from said core coder; a device (307) for perceptually weighting said residual signal (e). The perceptual weighting device includes a perceptually weighted filter (307) with gain compensation adapted to realize spectral continuity between the output signal of said perceptually weighted filter with gain compensation and the signal in the second sub-band. Application to transmitting and storing digital signals, such as audio-frequency speech, music, etc. signals.

Claims

1. A perceptual weighting device for coding/decoding of an audio signal in a given frequency band, said coding/decoding being effected in a plurality of adjacent sub-bands in said given frequency band, wherein said device includes, in at least one sub-band, a perceptually weighted filter (307) with gain compensation adapted to realize spectral continuity between the output signal of said perceptually weighted filter with gain compensation and the signals in the sub-bands adjacent to said sub-band.

2. The device according to claim 1, wherein said perceptually weighted filter (307) with gain compensation includes a perceptually weighted filter (501, 502) and a gain compensation module (503).

3. The device according to claim 2, wherein said gain compensation module (503) is disposed at the output of said perceptually weighted filter (501, 502).

4. The device according to claim 2, wherein said gain compensation module is disposed at the input of said perceptually weighted filter.

5. The device according to claim 1, wherein said perceptually weighted filter with gain compensation includes a perceptually weighted filter incorporating gain compensation.

6. The device according to claim 2, wherein said perceptually weighted filter is of the form Â

(z/γ

₁)/Â

(z/γ

₂) where Â

(z) represents a linear prediction filter and 0≦

γ

₂≦

1 and 0≦

γ

₁≦

1.

7. The device according to claim 6, wherein said gain compensation effects multiplication by a factor fac equal to:

$\mathrm{fac}=<br><br>\frac{\underset{i=0}{\overset{p}{\sum <br><br>}}<br><br><br><br>{\left(-{\mathrm{\gamma <br><br>}}_2\right)}^i<br><br>{\hat{a}}_i}{\underset{i=0}{\overset{p}{\sum <br><br>}}<br><br><br><br>{\left(-{\mathrm{\gamma <br><br>}}_1\right)}^i<br><br>{\hat{a}}_i}<br><br>$

where â

₁ are the coefficients of said linear prediction filter Â

(z)=â

₀+â

₁z<sup>−

1</sup>+â

₂z<sup>−

2</sup>+ . . . +â

_pz<sup>−

p</sup>.

8. A hierarchical audio coder for use in a frequency band divided into adjacent first and second sub-bands, said coder comprising:

a core coder (305;

905) for coding an original signal in a first sub-band of said frequency band;

a stage (306;

906) for calculating a residual signal (e) from said original signal and the signal from said core coder;

a device for perceptually weighting said residual signal (e);

wherein said perceptual weighting device includes a perceptually weighted filter (307;

907) with gain compensation adapted to realize spectral continuity between the output signal of said perceptually weighted filter with gain compensation and the signal in the second sub-band.

9. The coder according to claim 8, wherein said perceptually weighted filter (307) with gain compensation includes a perceptually weighted filter (501, 502) in the first sub-band.

10. The coder according to claim 9, wherein said perceptually weighted filter (501, 502) in the first sub-band is of the form Â

₁(z/γ

₁)/Â

₁(z/γ

₂) where Â

₁(z) represents a linear prediction filter and 0≦

γ

₂≦

1 and 0≦

γ

₁≦

1.

11. The coder according to claim 10, wherein gain compensation in the first sub-band effects a multiplication by a factor fac₁ equal to:

$\mathrm{fac}=<br><br>\frac{\underset{i=0}{\overset{p}{\sum <br><br>}}<br><br><br><br>{\left(-{\mathrm{\gamma <br><br>}}_2\right)}^i<br><br>{\hat{a}}_i}{\underset{i=0}{\overset{p}{\sum <br><br>}}<br><br><br><br>{\left(-{\mathrm{\gamma <br><br>}}_1\right)}^i<br><br>{\hat{a}}_i}<br><br>$

where â

_i are the coefficients of said linear prediction filter Â

₁(z)=â

₀+â

₁z<sup>−

1</sup>+â

₂z<sup>−

2</sup>+ . . . +â

_pz<sup>−

p</sup>.

12. The coder according to claim 10, wherein the coefficients of said linear prediction filter are supplied by said core coder (305).

13. The coder according to claim 8, wherein the signal from the perceptual weighting device (307) in the first sub-band and the original signal in the second sub-band are applied to respective transform analysis modules (308, 311) and said transform analysis modules are connected to a transform coder (313) in said frequency band.

14. The coder according to claim 8, wherein said coder includes also a perceptual weighting device for perceptually weighting the original signal in the second sub-band, comprising a perceptually weighted filter (912) with gain compensation adapted to realize spectral continuity between the output signal of said perceptually weighted filter (912) with gain compensation and the output signal of the perceptual weighting device (907) in the first sub-band.

15. The coder according to claim 14, wherein said perceptually weighted filter (912) with gain compensation includes a perceptually weighted filter in the second sub-band.

16. The coder according to claim 15, wherein said perceptually weighted filter in the second sub-band is of the form Â

₂(z/γ

′

₁)/Â

₂(z/γ

′

₂) where Â

₂(z) represents a linear prediction filter and 0≦

γ

′

₂≦

1 and 0≦

γ

′

₁≦

1.

17. The coder according to claim 16, wherein said gain compensation in the second sub-band effects multiplication by a factor fac₂ equal to:

${\mathrm{fac}}_2=<br><br>\frac{\underset{i=0}{\overset{p}{\sum <br><br>}}<br><br><br><br>{\left({\mathrm{\gamma <br><br>}}_2^{\mathrm{\prime <br><br>}}\right)}^i<br><br>\widehat{a_i^{\mathrm{\prime <br><br>}}}}{\underset{i=0}{\overset{p}{\sum <br><br>}}<br><br><br><br>{\left({\mathrm{\gamma <br><br>}}_1^{\mathrm{\prime <br><br>}}\right)}^i<br><br>\widehat{a_i^{\mathrm{\prime <br><br>}}}}<br><br>$

in which the â

′

_i are the coefficients of said linear prediction filter Â

₂(z)=â

′

₀+â

′

₁z<sup>−

1</sup>+â

′

₂z<sup>−

2</sup>+ . . . +â

′

_pz<sup>−

p</sup>.

18. The coder according to claim 16, wherein the coefficients of said linear prediction filter are supplied by a band expansion module (911).

19. The coder according to claim 14, wherein the signal from the perceptual weighting device (907) in the first sub-band and the signal from the perceptual weighting device (912) in the second sub-band are applied to respective transform analysis modules (908, 913) and said transform analysis modules are connected to a transform coder (914) in said frequency band.

20. The coder according to claim 8, wherein said core coder (305;

905) is a linear prediction based coder.

21. The coder according to claim 20, wherein said core coder (305;

905) is a CELP.

22. A hierarchical audio decoder for use in a frequency band divided into adjacent first and second sub-bands, said decoder comprising:

a core decoder (701;

1001) adapted to decode in the first sub-band of said frequency band a received signal coded by the coder according to claim 8; and

an inverse perceptual weighting device for inversely perceptually weighting a signal representing the residual signal (e) weighted in the first sub-band by the perceptual weighting device (307;

907) of said coder;

wherein said inverse perceptual weighting device (707;

1008) includes a perceptually weighted filter with gain compensation that is the inverse of the perceptually weighted filter (307) with gain compensation of the coder in the first sub-band.

23. The decoder according to claim 22, wherein said decoder also includes an inverse perceptual weighting device (1007) of the decoded signal in the second sub-band, comprising a perceptually weighted filter with gain compensation that is the inverse of the perceptually weighted filter with gain compensation of the coder in the second sub-band.

24. The decoder according to claim 23, wherein said inverse perceptually weighted filter with gain compensation includes an inverse perceptually weighted filter in the second sub-band.

25. The decoder according to claim 24, wherein said inverse perceptually weighted filter in the second sub-band is of the form Â

₂(z/γ

′

₂)/Â

₂(z/γ

′

₁), where 0≦

γ

′

₂≦

1 and 0≦

γ

′

₁≦

1.

26. The decoder according to claim 25, wherein the coefficients of the linear prediction filter Â

_2(z) are supplied by a band expansion module (1002).

27. A perceptual weighting method of coding an audio signal in a given frequency band, said coding being effected in a plurality of adjacent sub-bands in said frequency band, wherein said method includes, in at least one sub-band, a step of perceptual weighting with gain compensation adapted to realize spectral continuity between the signal from said perceptual weighting step with gain compensation and the signals in the sub-bands adjacent to said sub-band.

28. A method of perceptual weighting for decoding an audio signal coded in a given frequency band according to the method according to claim 27, wherein said method includes in said sub-band a step of perceptual weighting with gain compensation that is the inverse of said perceptual weighting step with gain compensation.

29. A computer program including a series of instructions stored on a medium for execution by a computer or a dedicated device, wherein execution of said instructions executes the perceptual weighting method according to claim 27.