Simultaneous time-domain and frequency-domain noise shaping for TDAC transforms

• US 8,626,517 B2
• Filed: 10/15/2010
• Issued: 01/07/2014
• Est. Priority Date: 10/15/2009
• Status: Active Grant

• Current Assignee: VoiceAge Corporation
• Original Assignee: VoiceAge Corporation
• Inventors: Bessette, Bruno
• Primary Examiner(s): Hudspeth, David R
• Assistant Examiner(s): Nguyen, Timothy
• Application Number:
  US12/905,750
• Publication Number:
  US 20110145003A1
• Time in Patent Office: 1,180 Days
• Field of Search: 704/500
• US Class Current: 704/500
• CPC Class Codes: G10L 19/0204 using subband decomposition
• CPC Class Codes: G10L 19/0212 using orthogonal transformation
• CPC Class Codes: G10L 19/032 Quantisation or dequantisation of spectral components
• CPC Class Codes: G10L 19/18 Vocoders using multiple modes
• CPC Class Codes: G10L 19/26 Pre-filtering or post-filtering
• CPC Class Codes: G10L 2019/0008 Algebraic codebooks
• CPC Class Codes: G10L 21/0208 Noise filtering

Abstract

A frequency-domain noise shaping method and device interpolates a spectral shape and a time-domain envelope of a quantization noise in a windowed and transform-coded audio signal. In the method and device, transform coefficients of the windowed and transform-coded audio signal are split into a plurality of spectral bands. For each spectral band, a first gain representing a spectral shape of the quantization noise at a first transition between a first time window and a second time window is calculated, a second gain representing a spectral shape of the quantization noise at a second transition between the second time window and a third time window is calculated, and the transform coefficients of the second time window are filtered based on the first and second gains, to interpolate between the first and second transitions the spectral shape and the time-domain envelope of the quantization noise.

Claims

1. A frequency-domain noise shaping method for interpolating a spectral shape and a time-domain envelope of a quantization noise in a windowed and transform-coded audio signal, comprising:

splitting transform coefficients of the windowed and transform-coded audio signal into a plurality of spectral bands; and

for each spectral band;

calculating a first gain representing, together with corresponding gains calculated for the other spectral bands, a spectral shape of the quantization noise at a first transition between a first time window and a second time window;

calculating a second gain representing, together with corresponding gains calculated for the other spectral bands, a spectral shape of the quantization noise at a second transition between the second time window and a third time window; and

an operation of filtering the transform coefficients of the second time window, the filtering operation receiving as first input the transform coefficients of the second time window and as second input the first and second gains to filter said transform coefficients of the second time window using the second input, first and second gains to interpolate between the first and second transitions the spectral shape and the time-domain envelope of the quantization noise.

3. The frequency-domain noise shaping method of claim 1, wherein calculating the first gain and calculating the second gain comprises applying a linear predictive coding to the windowed and transform-coded audio signal.

5. The frequency-domain noise shaping method of claim 1, wherein filtering the transform coefficients is made prior to quantization of the transform coefficients producing the quantization noise.

6. The frequency-domain noise shaping method of claim 1, wherein filtering the transform coefficients is made after quantization of the transform coefficients producing the quantization noise.

7. The frequency-domain noise shaping method of claim 1, wherein filtering the transform coefficients comprises filtering the transform coefficients prior to quantization of the transform coefficients producing the quantization noise, and inverse filtering the transform coefficients after quantization of said transform coefficients.

9. The frequency-domain noise shaping method of claim 1, further comprising, following filtering of the transform coefficients in each of the spectral bands:

quantizing the filtered transform coefficients;

encoding the quantized, filtered transform coefficients; and

transmitting the encoded, quantized, filtered transform coefficients to a receiver or storing the encoded, quantized, filtered transform coefficients in a storage device.

10. The frequency-domain noise shaping method of claim 1, further comprising:

receiving from a transceiver or retrieving from a storage device filtered, quantized and encoded transform coefficients;

decoding the filtered, quantized and encoded transform coefficients; and

inverse quantizing the decoded, filtered and quantized transform coefficients.

2. A frequency-domain noise shaping method for interpolating a spectral shape and a time-domain envelope of a quantization noise in a windowed and transform-coded audio signal, comprising:

splitting transform coefficients of the windowed and transform-coded audio signal into a plurality of spectral bands; and

for each spectral band;

calculating a first gain representing, together with corresponding gains calculated for the other spectral bands, a spectral shape of the quantization noise at a first transition between a first time window and a second time window;

calculating a second gain representing, together with corresponding gains calculated for the other spectral bands, a spectral shape of the quantization noise at a second transition between the second time window and a third time window; and

an operation of filtering the transform coefficients of the second time window, the filtering operation receiving as first input the transform coefficients of the second time window and as second input the first and second gains to filter said transform coefficients of the second time window using the second input, first and second gains to interpolate between the first and second transitions the spectral shape and the time-domain envelope of the quantization noise;

wherein the windowed and transform-coded audio signal is windowed using successive overlapping windows,

wherein the first gain is a noise gain calculated at a middle point of an overlap between the first and second time windows, and

wherein the second gain is a noise gain calculated at a middle point of an overlap between the second and third time windows.

4. A frequency-domain noise shaping method for interpolating a spectral shape and a time-domain envelope of a quantization noise in a windowed and transform-coded audio signal, comprising:

splitting transform coefficients of the windowed and transform-coded audio signal into a plurality of spectral bands; and

for each spectral band;

calculating a first gain representing, together with corresponding gains calculated for the other spectral bands, a spectral shape of the quantization noise at a first transition between a first time window and a second time window;

calculating a second gain representing, together with corresponding gains calculated for the other spectral bands, a spectral shape of the quantization noise at a second transition between the second time window and a third time window; and

an operation of filtering the transform coefficients of the second time window, the filtering operation receiving as first input the transform coefficients of the second time window and as second input the first and second gains to filter said transform coefficients of the second time window using the second input, first and second gains to interpolate between the first and second transitions the spectral shape and the time-domain envelope of the quantization noise;

wherein filtering the transform coefficients comprises achieving a desired spectral shape of the quantization noise at the first and second transitions and a smooth transition of an envelope of this spectral shape from the first transition to the second transition.

8. A frequency-domain noise shaping method for interpolating a spectral shape and a time-domain envelope of a quantization noise in a windowed and transform-coded audio signal, comprising:

splitting transform coefficients of the windowed and transform-coded audio signal into a plurality of spectral bands; and

for each spectral band;

calculating a first gain representing, together with corresponding gains calculated for the other spectral bands, a spectral shape of the quantization noise at a first transition between a first time window and a second time window;

calculating a second gain representing, together with corresponding gains calculated for the other spectral bands, a spectral shape of the quantization noise at a second transition between the second time window and a third time window; and

an operation of filtering the transform coefficients of the second time window, the filtering operation receiving as first input the transform coefficients of the second time window and as second input the first and second gains to filter said transform coefficients of the second time window using the second input, first and second gains to interpolate between the first and second transitions the spectral shape and the time-domain envelope of the quantization noise;

wherein filtering the transform coefficients comprises calculating filter parameters on the basis of the first and second calculated gains.

11. A frequency-domain noise shaping device for interpolating a spectral shape and a time-domain envelope of a quantization noise in a windowed and transform-coded audio signal having transform coefficients, comprising:

a processor comprising;

a splitter module configured to split the transform coefficients of the windowed and transform-coded audio signal into a plurality of spectral bands;

a calculator module configured to calculate, for each spectral band, a first gain representing, together with corresponding gains calculated for the other spectral bands, a spectral shape of the quantization noise at a first transition between a first time window and a second time window, and a second gain representing, together with corresponding gains calculated for the other spectral bands, a spectral shape of the quantization noise at a second transition between the second time window and a third time window; and

a filter module configured to filter the transform coefficients of the second time window, the filter module receiving as first input the transform coefficients of the second time window and as second input the first and second gains to filter said transform coefficients of the second time window using the second input, first and second gains to interpolate between the first and second transitions the spectral shape and the time-domain envelope of the quantization noise.

13. The frequency-domain noise shaping device of claim 11, wherein the gain calculator module applies a linear predictive coding to the windowed and transform-coded audio signal in order to calculate the first gain and the second gain.

15. The frequency-domain noise shaping device of claim 11, wherein the transform coefficient filter module filters the transform coefficients prior to quantization of the transform coefficients producing the quantization noise.

16. The frequency-domain noise shaping device of claim 11, wherein the transform coefficient filter module filters the transform coefficients after quantization of the transform coefficients producing the quantization noise.

17. The frequency-domain noise shaping device of claim 11, wherein the transform coefficient filter module filters the transform coefficients prior to quantization of the transform coefficients producing the quantization noise, and inverse filters the transform coefficients after quantization of said transform coefficients.

19. The frequency-domain noise shaping device of claim 11 wherein, following filtering of the transform coefficients in each of the spectral bands, the processor:

quantizes the filtered transform coefficients;

encodes the quantized, filtered transform coefficients; and

transmits the encoded, quantized, filtered transform coefficients to a transceiver or stores the encoded, quantized, filtered transform coefficients in a storage device.

20. The frequency-domain noise shaping device of claim 11, wherein the processor:

receives from a transceiver or retrieves from a storage device filtered, quantized and encoded transform coefficients;

decodes the filtered, quantized and encoded transform coefficients; and

inverse quantizes the decoded, filtered and quantized transform coefficients.

21. An encoder for encoding a windowed audio signal, comprising:

a first coder of the windowed audio signal using a time-domain coding mode;

a second coder of the windowed audio signal using a transform-domain coding mode using a psychoacoustic model and producing a windowed and transform-coded audio signal;

a selector between the first coder using the time-domain coding mode and the second coder using the transform-domain coding mode when encoding a time window of the windowed audio signal; and

a frequency-domain noise shaping device according to claim 11 for interpolating a spectral shape and a time-domain envelope of a quantization noise in the windowed and transform-coded audio signal, thereby achieving a desired spectral shape of the quantization noise at the first and second transitions and a smooth transition of an envelope of this spectral shape from the first transition to the second transition.

22. The encoder of claim 21, wherein the time-domain coding mode is ACELP and the transform-domain coding mode uses a MDCT.

23. The encoder of claim 21, wherein the frequency-domain noise shaping device uses, as the first and second gains, noise gains calculated from an LPC filter, scale factors calculated from the psychoacoustic model, or a combination of the noise gains and scale factors.

24. The encoder of claim 23, wherein the combination of the noise gains and scale factors comprises the sum of the noise gains and scale factors, where the scale factors are used as a correction to the noise gains.

25. The encoder of claim 21, wherein the frequency-domain noise shaping device uses, as the first and second gains, noise gains calculated from an LPC filter and a second set of gains or scale factors, used as a correction to the noise gains.

26. A decoder for decoding an encoded, windowed audio signal, comprising:

a first decoder of the encoded, windowed audio signal using a time-domain decoding mode;

a second decoder of the encoded, windowed audio signal using a transform-domain decoding mode using a psychoacoustic model; and

a selector between the first decoder using the time-domain decoding mode and the second decoder using the transform-domain decoding mode when decoding a time window of the encoded, windowed audio signal; and

a frequency-domain noise shaping device according to claim 11 for interpolating a spectral shape and a time-domain envelope of a quantization noise in transform-coded windows of the encoded, windowed audio signal, thereby achieving a desired spectral shape of the quantization noise at the first and second transitions and a smooth transition of an envelope of this spectral shape from the first transition to the second transition.

27. The decoder of claim 26, wherein the time-domain decoding mode is ACELP and the transform-domain decoding mode uses a MDCT.

28. The decoder of claim 26, wherein the frequency-domain noise shaping device uses, as the first and second gains, noise gains calculated from an LPC filter, scale factors calculated from the psychoacoustic model, or a combination of the noise gains and scale factors.

29. The decoder of claim 28, wherein the combination of noise gains and scale factors comprises the sum of the noise gains and scale factors, where the scale factors are used as a correction to the noise gains.

30. The decoder of claim 26, wherein the frequency-domain noise shaping device uses, as the first and second gains, noise gains calculated from an LPC filter and a second set of gains or scale factors, used as a correction to the noise gains.

31. The frequency-domain noise shaping device of claim 11 further comprising:

a storage device,

wherein the processor is operably connected to the storage device for storing or retrieving the filtered transform coefficients.

32. The frequency-domain noise shaping device of claim 11 further comprising:

a transceiver,

wherein the processor is operably connected to the transceiver for sending or receiving the filtered transform coefficients.

12. A frequency-domain noise shaping device for interpolating a spectral shape and a time-domain envelope of a quantization noise in a windowed and transform-coded audio signal having transform coefficients, comprising:

a processor comprising;

a splitter module configured to split the transform coefficients of the windowed and transform-coded audio signal into a plurality of spectral bands;

a calculator module configured to calculate, for each spectral band, a first gain representing, together with corresponding gains calculated for the other spectral bands, a spectral shape of the quantization noise at a first transition between a first time window and a second time window, and a second gain representing, together with corresponding gains calculated for the other spectral bands, a spectral shape of the quantization noise at a second transition between the second time window and a third time window; and

a filter module configured to filter the transform coefficients of the second time window, the filter module receiving as first input the transform coefficients of the second time window and as second input the first and second gains to filter said transform coefficients of the second time window using the second input, first and second gains to interpolate between the first and second transitions the spectral shape and the time-domain envelope of the quantization noise;

wherein the windowed and transform-coded audio signal is windowed using successive overlapping windows, and wherein the calculator module calculates the first gain at a middle point of an overlap between the first and second time windows, and the second gain at a middle point of an overlap between the second and third time window.

33. The frequency-domain noise shaping device of claim 12 further comprising:

a storage device,

wherein the processor is operably connected to the storage device for storing or retrieving the filtered transform coefficients.

34. The frequency-domain noise shaping device of claim 12 further comprising:

a transceiver,

wherein the processor is operably connected to the transceiver for sending or receiving the filtered transform coefficients.

14. A frequency-domain noise shaping device for interpolating a spectral shape and a time-domain envelope of a quantization noise in a windowed and transform-coded audio signal having transform coefficients, comprising:

a processor comprising;

a splitter module configured to split the transform coefficients of the windowed and transform-coded audio signal into a plurality of spectral bands;

a calculator module configured to calculate, for each spectral band, a first gain representing, together with corresponding gains calculated for the other spectral bands, a spectral shape of the quantization noise at a first transition between a first time window and a second time window, and a second gain representing, together with corresponding gains calculated for the other spectral bands, a spectral shape of the quantization noise at a second transition between the second time window and a third time window; and

a filter module configured to filter the transform coefficients of the second time window, the filter module receiving as first input the transform coefficients of the second time window and as second input the first and second gains to filter said transform coefficients of the second time window using the second input, first and second gains to interpolate between the first and second transitions the spectral shape and the time-domain envelope of the quantization noise,

wherein the transform coefficient filter module achieves a desired spectral shape of the quantization noise at the first and second transitions and a smooth transition of an envelope of this spectral shape from the first transition to the second transition.

35. The frequency-domain noise shaping device of claim 14 further comprising:

a storage device,

wherein the processor is operably connected to the storage device for storing or retrieving the filtered transform coefficients.

36. The frequency-domain noise shaping device of claim 14 further comprising:

a transceiver,

wherein the processor is operably connected to the transceiver for sending or receiving the filtered transform coefficients.

18. A frequency-domain noise shaping device for interpolating a spectral shape and a time-domain envelope of a quantization noise in a windowed and transform-coded audio signal having transform coefficients, comprising:

a processor comprising;

a splitter module configured to split the transform coefficients of the windowed and transform-coded audio signal into a plurality of spectral bands;

a calculator module configured to calculate, for each spectral band, a first gain representing, together with corresponding gains calculated for the other spectral bands, a spectral shape of the quantization noise at a first transition between a first time window and a second time window, and a second gain representing, together with corresponding gains calculated for the other spectral bands, a spectral shape of the quantization noise at a second transition between the second time window and a third time window; and

a filter module configured to filter the transform coefficients of the second time window, the filter module receiving as first input the transform coefficients of the second time window and as second input the first and second gains to filter said transform coefficients of the second time window using the second input, first and second gains to interpolate between the first and second transitions the spectral shape and the time-domain envelope of the quantization noise,

wherein the transform coefficient filter module calculates filter parameters on the basis of the first and second calculated gains.

37. The frequency-domain noise shaping device of claim 18 further comprising:

a storage device,

wherein the processor is operably connected to the storage device for storing or retrieving the filtered transform coefficients.

38. The frequency-domain noise shaping device of claim 18 further comprising:

a transceiver,

wherein the processor is operably connected to the transceiver for sending or receiving the filtered transform coefficients.