Advanced quantizer

• US 9,940,942 B2
• Filed: 04/04/2014
• Issued: 04/10/2018
• Est. Priority Date: 04/05/2013
• Status: Active Grant

• Current Assignee: Dolby International AB (Dolby Laboratories Incorporated)
• Original Assignee: Dolby International AB (Dolby Laboratories Incorporated)
• Inventors: Klejsa, Janusz, Villemoes, Lars, Hedelin, Per
• Primary Examiner(s): Saint Cyr, Leonard
• Application Number:
  US14/781,700
• Publication Number:
  US 20160042744A1
• Time in Patent Office: 1,467 Days
• Field of Search: 704222, 704226, 704230
• CPC Class Codes: G10L 19/005 Correction of errors induced by the transmission channel, if related to the coding algorithm
• CPC Class Codes: G10L 19/028 Noise substitution, i.e. substituting non-tonal spectral components by noisy source comfort noise for discontinuous speech transmission G10L19/012
• CPC Class Codes: G10L 19/035 Scalar quantisation
• CPC Class Codes: G10L 19/20 using sound class specific coding, hybrid encoders or object based coding

Abstract

The present document relates an audio encoding and decoding system (referred to as an audio codec system). In particular, the present document relates to a transform-based audio codec system which is particularly well suited for voice encoding/decoding. A quantization unit configured to quantize a first coefficient of a block of coefficients is described. The block of coefficients comprises a plurality of coefficients for a plurality of corresponding frequency bins. The quantization unit is configured to provide a set of quantizers. The set of quantizers comprises a plurality of different quantizers associated with a plurality of different signal-to-noise ratios, referred to as SNR, respectively. The plurality of different quantizers includes a noise-filling quantizer; one or more dithered quantizers; and one or more un-dithered quantizers. The quantization unit is further configured to determine an SNR indication indicative of a SNR attributed to the first coefficient, and to select a first quantizer from the set of quantizers, based on the SNR indication. In addition, the quantization unit is configured to quantize the first coefficient using the first quantizer.

Claims

1. A quantization system configured to quantize a first coefficient of a block of coefficients derived from an audio signal;

wherein the block of coefficients comprises a plurality of coefficients for a plurality of corresponding frequency bins;

wherein the quantization system is configured to encode audio data based on the first coefficient by;

providing a set of quantizers;

wherein the set of quantizers comprises a limited number of different quantizers yielding different signal-to-noise ratios, referred to as SNR, respectively;

wherein the different quantizers of the set of quantizers are ordered according to their SNR;

the set of quantizers including a noise-filling quantizer;

wherein the noise-filling quantizer is configured to quantize the first coefficient by replacing a value of the first coefficient with a random value generated according to a pre-determined statistical model;

wherein the noise-filling quantizer is used for a zero bit-rate situation;

one or more dithered quantizers; and

one or more un-dithered deterministic quantizers;

determining an SNR indication indicative of an SNR attributed to the first coefficient;

selecting a first quantizer yielding a particular SNR from the set of quantizers, based on the SNR indication; and

quantizing the first coefficient using the first quantizer;

wherein the quantization system includes one or more processors comprised in on or more computing devices to encode the audio data based upon the first coefficient.

2. The quantization system of claim 1, wherein

the noise-filling quantizer is associated with a relatively lowest SNR of the different SNRs;

the one or more un-dithered deterministic quantizers are associated with one or more relatively highest SNRs of the different SNRs; and

the one or more dithered quantizers are associated with one or more intermediate SNRs, higher than the relatively lowest SNR and lower than the one or more relatively highest SNRs of the different SNRs.

3. The quantization system of claim 1, wherein the set of quantizers is ordered in accordance to increasing SNRs associated with the different quantizers.

4. The quantization system of claim 3, wherein

an SNR difference is given by the difference of the SNRs associated with a pair of adjacent quantizers from the ordered set of quantizers;

and

the SNR differences for all pairs of adjacent quantizers from the different quantizers fall within a pre-determined SNR difference interval centered around a pre-determined SNR target difference.

5. The quantization system of claim 1, wherein the noise-filling quantizer

comprises a random number generator configured to generate random numbers according to the pre-determined statistical model;

and/or

is associated with a SNR that is essentially lower or equal to 0 dB.

6. The quantization system of claim 1, wherein a particular dithered quantizer of the one or more dithered quantizers comprises

a dither application unit configured to determine a first dithered coefficient by applying a dither value to the first coefficient;

and

a scalar quantizer configured to determine a first quantization index by assigning the first dithered coefficient to an interval of the scalar quantizer.

7. The quantization system of claim 6, wherein the particular dithered quantizer of the one or more dithered quantizers further comprises

an inverse scalar quantizer configured to assign a first reconstruction value to the first quantization index;

a dither removal unit configured to determine a first de-dithered coefficient by removing the dither value from the first reconstruction value.

8. The quantization system of claim 6, wherein

the scalar quantizer has a pre-determined quantizer step size Δ

;

the dither value takes on values from a pre-determined dither interval; and

the pre-determined dither interval has a width equal to or smaller than the pre-determined quantizer step size Δ

.

9. The quantization system of claim 1, wherein

the block of coefficients is associated with a spectral block envelope;

the spectral block envelope is indicative of a plurality of spectral energy values for the plurality of frequency bins; and

the SNR indication depends on the spectral block envelope.

10. The quantization system of claim 1, wherein

the plurality of coefficients of the block of coefficients is assigned to a plurality of frequency bands;

a frequency band comprises one or more frequency bins; and

the quantization system is configured to select a quantizer from the set of quantizers for each of the plurality of frequency bands, such that coefficients which are assigned to a same frequency band are quantized using the same quantizer.

11. The quantization system of claim 1, wherein the quantization system is configured to

determine side information indicative of a property of the block of coefficients;

and

generate the set of quantizers in dependence of the side information.

12. An inverse quantization system configured to de-quantize quantization indices;

wherein the quantization indices are associated with a block of coefficients comprising a plurality of coefficients for a plurality of corresponding frequency bins;

wherein the block of coefficients is derived from an audio signal;

wherein the inverse quantization system is configured to decode audio data based upon first coefficient by;

providing a set of quantizers;

wherein the set of quantizers comprises a limited number of different quantizers yielding different signal-to-noise ratios, referred to as SNR, respectively;

wherein the different quantizers of the set of quantizers are ordered according to their SNR;

the set of quantizers including a noise-filling quantizer;

wherein the noise-filling quantizer is configured to quantize a coefficient by replacing a value of the coefficient with a random value generated according to a pre-determined statistical model;

wherein the noise-filling quantizer is used for a zero bit-rate situation;

one or more dithered quantizers; and

one or more un-dithered deterministic quantizers;

determining an SNR indication indicative of an SNR attributed to a first coefficient from the block of coefficients;

selecting a first quantizer yielding a particular SNR from the set of quantizers, based on the SNR indication; and

determining a first quantized coefficient for the first coefficient using the first quantizer;

wherein the inverse quantization system includes one or more processors comprised in one or more computing devices to decode the audio data based upon first coefficient.

13. A method for quantizing a first coefficient of a block of coefficients derived from an audio signal;

wherein the block of coefficients comprises a plurality of coefficients for a plurality of corresponding frequency bins to encode audio data based upon first coefficient;

wherein the method comprises

a. providing a set of quantizers;

wherein the set of quantizers comprises a plurality of different quantizers associated with a plurality of different signal-to-noise ratios, referred to as SNR, respectively, the plurality of different quantizers including

i. a noise-filling quantizer;

wherein the noise-filling quantizer is configured to quantize the first coefficient by replacing a value of the first coefficient with a random value generated according to a pre-determined statistical model;

wherein the noise-filling quantizer is used for a zero bit-rate situation;

ii. one or more dithered quantizers; and

iii. one or more un-dithered deterministic quantizers;

b. determining an SNR indication indicative of a SNR attributed to the first coefficient;

c. selecting a first quantizer from the set of quantizers, based on the SNR indication; and

d. quantizing the first coefficient using the first quantizer,

wherein the method is performed by one or more processors comprised in one or more computing devices to encode the audio data based upon first coefficient.

14. A method for de-quantizing quantization indices for decoding audio data based upon first coefficient;

wherein the quantization indices are associated with a block of coefficients comprising a plurality of coefficients for a plurality of corresponding frequency bins;

wherein the block of coefficients is derived from an audio signal;

wherein the method comprises

a. providing a set of quantizers;

wherein the set of quantizers comprises a plurality of different quantizers associated with a plurality of different signal-to-noise ratios, referred to as SNR, respectively, the plurality of different quantizers including

i. a noise-filling quantizer;

wherein the noise-filling quantizer is configured to quantize a coefficient by replacing a value of the coefficient with a random value generated according to a pre-determined statistical model;

wherein the noise-filling quantizer is used for a zero bit-rate situation;

ii. one or more dithered quantizers; and

iii. one or more un-dithered deterministic quantizers;

b. determining an SNR indication indicative of a SNR attributed to a first coefficient from the block of coefficients;

c. selecting a first quantizer yielding a particular SNR from the set of quantizers, based on the SNR indication; and

d. determining a first quantized coefficient for the first coefficient using the first quantizer,

wherein the method is performed by one or more processors comprised in one or more computing devices for decoding the audio data based upon first coefficient.