Sinusoidal model based coding of audio signals

• US 7,120,587 B2
• Filed: 10/31/2001
• Issued: 10/10/2006
• Est. Priority Date: 11/03/2000
• Status: Expired due to Fees

• Current Assignee: Pendragon Wireless LLC (Pendrell Corporation)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Kleijn, Willem Bastiaan, Heusdens, Richard, Vafin, Renat
• Primary Examiner(s): SAINT CYR, LEONARD
• Application Number:
  US10/169,345
• Publication Number:
  US 20030009332A1
• Time in Patent Office: 1,805 Days
• Field of Search: 704/200.1, 704/203, 704/205, 704/503
• US Class Current: 704/500
• CPC Class Codes: G10L 19/02 using spectral analysis, e.g. transform vocoders or subband vocoders
• CPC Class Codes: G10L 2019/0014 Selection criteria for distances
• CPC Class Codes: G10L 21/0364 for improving intelligibility

Abstract

An apparatus and method of signal coding includes an analysis-by-synthesis algorithm for sinusoidal modeling. An input signal to be modeled is divided in time to produce a plurality of frames. Functions from a dictionary are selected to form an approximation of the section of the input signal contained in each frame, with the selection carried out based on a psychoacoustic norm. The function dictionary is made up of complex exponentials and these are selected iteratively to make up the section of the input signal contained in each frame. The psychoacoustic norm adapts after each iteration according to the changing masking threshold of the residual signal to be modeled in the next step.

Claims

1. A method of signal coding, the method comprising the acts of:

(a) receiving an input signal;

(b) dividing the input signal in time to produce a plurality of frames each containing a section of the input signal; and

(c) selecting functions from a function dictionary to form an approximation of the signal in each frame, the selecting act being carried out in sub-acts;

wherein the selection process of act (c) is carried out on the basis of a norm which is based on a combination, such as a product, of a weighting function expressed as a function of frequency and a product of a window function defining each frame in the plurality of frames and the section of the input signal to be modeled, the product of the window function and the section of the input signal to be modeled being expressed as a function of frequency; and

wherein a new norm is induced at each of said sub-acts based on a current residual signal, the weighting function being updated to take into account masking characteristics of the residual signal.

2. The method of signal coding according to claim 1, wherein the norm is defined by

∥

Rx∥

=√

{square root over (∫

{overscore (a)}(ƒ

)|({overscore (wRx)})(ƒ

)|²dƒ

)}

in which Rx represents a section of the input signal to be modeled, ā

(ƒ

) represents the weighting function expressed as a function of frequency and ({overscore (wRx)})(ƒ

) represents the transform, such as a Fourier transform, of the product of the window function defining each frame in the plurality of frames, w, and Rx.

3. The method of signal coding according to claim 1, wherein the weighting function incorporates knowledge of the psychoacoustics of human hearing to aid the selecting act.

4. The method of signal coding according to claim 3, wherein the knowledge of the psychoacoustics of human hearing is incorporated into the norm through the function ā

(ƒ

).

5. The method of signal coding according to claim 4, wherein ā

(ƒ

) is based on the masking threshold of the human auditory system and is the inverse of the masking threshold.

6. The method of signal coding according to claim 5, wherein ā

(ƒ

) is computed using a known model of the masking threshold.

7. The method of signal coding according to claim 1, wherein in each of said sub-acts a single function from a function dictionary being identified.

8. The method of signal coding according to claim 7, wherein the function identified at a first sub-act of said sub-acts is subtracted from the input signal in the frame to form a residual signal and at each subsequent sub-act of said sub-acts a function is identified and subtracted from the residual signal to form a further residual signal, with the sum of the functions identified at each of said sub-acts forming an approximation of the signal in each frame.

9. The method of signal coding according to claim 1, wherein the norm adapts at each of said sub-acts.

10. The method of signal coding according to claim 1, wherein the function ā

(ƒ

) is based on the masking threshold of the human auditory system, is the inverse of the masking threshold for the section of an input signal in a frame being coded and is calculated using a known model of the masking threshold.

11. The method of claim 1, wherein the norm is induced according to the inner product:

12. The method of audio coding according to claim 11, wherein denoting a residual at iteration m as R^mx and the weighting function from a previous iteration ā

<sub>m−

1</sub> a function identified from the function dictionary minimizes ∥

R^mx∥

<sub>ā

m−

1</sub>, with ∥

*∥

<sub>ā

m−

1</sub> representing the norm calculated using ā

<sub>m−

1</sub>.

13. The method of signal coding according claim 1, wherein convergence of the method of signal coding is guaranteed by validity of a theorem that for all m>

0 there exists a λ

>

0 such that ∥

R^mx∥

<sub>ā

m</sub>≦

2<sup>−

λ

m</sup>∥

x∥

<sub>ā

0</sub>, where x represents an initial section of the input signal to be modeled.

14. The method of signal coding according to claim 11, wherein the selecting act is carried out in sub-acts, and wherein the convergence of the method of audio coding is guaranteed by the increase or invariance in each frame of the masking threshold at each of said sub-acts, such that ā

_m(ƒ

)≦

ā

<sub>m−

1</sub>(ƒ

) over the entire frequency range ƒ

ε

[0,1).

15. The method of signal coding according to claim 1, wherein the window function is any one of a Hanning window, a Hamming window, a rectangular window or another suitable window.

16. A coding apparatus operating an accordance with the method of claim 1.

17. A transmitting apparatus comprising;

a source for providing an input signal;

a coding apparatus according to claim 16 for coding the input signal to obtain a coded signal, and

an output unit for outputting the coded signal.