DEVICE AND METHOD FOR REDUCING QUANTIZATION NOISE IN A TIME-DOMAIN DECODER

• US 20140249807A1
• Filed: 03/04/2014
• Published: 09/04/2014
• Est. Priority Date: 03/04/2013
• Status: Active Grant

• Current Assignee: VoiceAge EVS LLC (SoftBank Group Corp.)
• Original Assignee: VoiceAge Corporation
• Inventors: Jelinek, Milan, VAILLANCOURT, Tommy
• Granted Patent: US 9,384,755 B2
• Time in Patent Office: Days
• US Class Current: 704/207
• CPC Class Codes: G10L 19/08 Determination or coding of the excitation function; Determination or coding of the long-term prediction parameters
• CPC Class Codes: G10L 19/12 the excitation function being a code excitation, e.g. in code excited linear prediction [CELP] vocoders
• CPC Class Codes: G10L 19/26 Pre-filtering or post-filtering
• CPC Class Codes: G10L 21/0208 Noise filtering
• CPC Class Codes: G10L 21/0224 Processing in the time domain
• CPC Class Codes: G10L 21/0232 Processing in the frequency domain
• CPC Class Codes: G10L 25/21 the extracted parameters being power information
• CPC Class Codes: G10L 25/78 Detection of presence or absence of voice signals switching of direction of transmission by voice frequency in two-way loud-speaking telephone systems H04M9/10
• CPC Class Codes: G10L 25/93 Discriminating between voiced and unvoiced parts of speech signals G10L25/90 takes precedence

Abstract

The present disclosure relates to a device and method for reducing quantization noise in a signal contained in a time-domain excitation decoded by a time-domain decoder. The decoded time-domain excitation is converted into a frequency-domain excitation. A weighting mask is produced for retrieving spectral information lost in the quantization noise. The frequency-domain excitation is modified to increase spectral dynamics by application of the weighting mask. The modified frequency-domain excitation is converted into a modified time-domain excitation. The method and device can be used for improving music content rendering of linear-prediction (LP) based codecs. Optionally, a synthesis of the decoded time-domain excitation may be classified into one of a first set of excitation categories and a second set of excitation categories, the second set including INACTIVE or UNVOICED categories, the first set including an OTHER category.

Claims

1. A device for reducing quantization noise in a signal contained in a time-domain excitation decoded by a time-domain decoder, comprising:

a converter of the decoded time-domain excitation into a frequency-domain excitation;

a mask builder to produce a weighting mask for retrieving spectral information lost in the quantization noise;

a modifier of the frequency-domain excitation to increase spectral dynamics by application of the weighting mask; and

a converter of the modified frequency-domain excitation into a modified time-domain excitation.

2. A device according to claim 1, comprising:

a classifier of a synthesis of the decoded time-domain excitation into one of a first set of excitation categories and a second set of excitation categories;

wherein, the second set of excitation categories comprises INACTIVE or UNVOICED categories; and

the first set of excitation categories comprises an OTHER category.

3. A device according to claim 2, wherein the converter of the decoded time-domain excitation into a frequency-domain excitation applies to the decoded time-domain excitation classified in the first set of excitation categories.

4. A device according to claim 2, wherein the classifier of the synthesis of the decoded time-domain excitation into one of a first set of excitation categories and a second set of excitation categories uses classification information transmitted from an encoder to the time-domain decoder and retrieved at the time-domain decoder from a decoded bitstream.

5. A device according to claim 2, comprising a first synthesis filter to produce a synthesis of the modified time-domain excitation.

6. A device according to claim 5, comprising a second synthesis filter to produce the synthesis of the decoded time-domain excitation.

7. A device according to claim 5, comprising a de-emphasizing filter and resampler to generate a sound signal from one of the synthesis of the decoded time-domain excitation and of the synthesis of the modified time-domain excitation.

8. A device according to claim 5, comprising a two-stage classifier for selecting an output synthesis as:

the synthesis of the decoded time-domain excitation when the time-domain excitation is classified in the second set of excitation categories; and

the synthesis of the modified time-domain excitation when the time-domain excitation is classified in the first set of excitation categories.

9. A device according to claim 1, comprising an analyzer of the frequency-domain excitation to determine whether the frequency-domain excitation contains music.

10. A device according to claim 9, wherein the analyzer of the frequency-domain excitation determines that the frequency-domain excitation contains music by comparing a statistical deviation of spectral energy differences of the frequency-domain excitation with a threshold.

11. A device according to claim 1, comprising an excitation extrapolator to evaluate an excitation of future frames, whereby conversion of the modified frequency-domain excitation into a modified time-domain excitation is delay-less.

12. A device according to claim 11, wherein the excitation extrapolator concatenates past, current and extrapolated time-domain excitation.

13. A device according to claim 1, wherein the mask builder produces the weighting mask using time averaging or frequency averaging, or a combination of time and frequency averaging.

14. A device according to claim 1, comprising a noise reductor to estimate a signal to noise ratio in a selected band of the decoded time-domain excitation and to perform a frequency-domain noise reduction based on the signal to noise ratio.

15. A method for reducing quantization noise in a signal contained in a time-domain excitation decoded by a time-domain decoder, comprising:

converting, by the time-domain decoder, the decoded time-domain excitation into a frequency-domain excitation;

producing a weighting mask for retrieving spectral information lost in the quantization noise;

modifying the frequency-domain excitation to increase spectral dynamics by application of the weighting mask; and

converting the modified frequency-domain excitation into a modified time-domain excitation.

16. A method according to claim 15, comprising:

classifying a synthesis of the decoded time-domain excitation into one of a first set of excitation categories and a second set of excitation categories;

wherein, the second set of excitation categories comprises INACTIVE or UNVOICED categories; and

the first set of excitation categories comprises an OTHER category.

17. A method according to claim 16, comprising applying a conversion of the decoded time-domain excitation into a frequency-domain excitation to the decoded time-domain excitation classified in the first set of excitation categories.

18. A method according to claim 16, comprising using classification information transmitted from an encoder to the time-domain decoder and retrieved at the time-domain decoder from a decoded bitstream to classify the synthesis of the decoded time-domain excitation into the one of a first set of excitation categories and a second set of excitation categories.

19. A method according to claim 16, comprising producing a synthesis of the modified time-domain excitation.

20. A method according to claim 19, comprising generating a sound signal from one of the synthesis of the decoded time-domain excitation and of the synthesis of the modified time-domain excitation.

21. A method according to claim 19, comprising selecting an output synthesis as:

the synthesis of the decoded time-domain excitation when the time-domain excitation is classified in the second set of excitation categories; and

the synthesis of the modified time-domain excitation when the time-domain excitation is classified in the first set of excitation categories.

22. A method according to claim 15, comprising analyzing the frequency-domain excitation to determine whether the frequency-domain excitation contains music.

23. A method according to claim 22, comprising determining that the frequency-domain excitation contains music by comparing a statistical deviation of spectral energy differences of the frequency-domain excitation with a threshold.

24. A method according to claim 15, comprising evaluating an extrapolated excitation of future frames, whereby conversion of the modified frequency-domain excitation into a modified time-domain excitation is delay-less.

25. A method according to claim 24, comprising concatenating past, current and extrapolated time-domain excitation.

26. A method according to claim 15, wherein the weighting mask is produced using time averaging or frequency averaging or a combination of time and frequency averaging.

27. A method according to claim 15, comprising:

estimating a signal to noise ratio in a selected band of the decoded time-domain excitation; and

performing a frequency-domain noise reduction based on the estimated signal to noise ratio.