Non-speech content for low rate CELP decoder

• US 9,252,728 B2
• Filed: 11/02/2012
• Issued: 02/02/2016
• Est. Priority Date: 11/03/2011
• Status: Active Grant

• Current Assignee: VoiceAge EVS LLC (FIG LLC (d/b/a Fortress Investment Group LLC))
• Original Assignee: VoiceAge Corporation
• Inventors: Vaillancourt, Tommy, Jelinek, Milan
• Primary Examiner(s): Paul, Disler
• Application Number:
  US13/667,921
• Publication Number:
  US 20130121508A1
• Time in Patent Office: 1,187 Days
• Field of Search: 381/22, 381/98, 704/206, 704/500, 704/E19.001, 704/219
• US Class Current: 1/1
• 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 19/20 using sound class specific coding, hybrid encoders or object based coding
• CPC Class Codes: G10L 19/22 Mode decision, i.e. based on audio signal content versus external parameters
• CPC Class Codes: G10L 19/26 Pre-filtering or post-filtering
• 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 25/81 for discriminating voice from music
• CPC Class Codes: G10L 25/93 Discriminating between voiced and unvoiced parts of speech signals G10L25/90 takes precedence
• CPC Class Codes: H03G 3/20 Automatic control H03G3/005 takes precedence; combined with volume compression or expansion H03G7/00

Abstract

A method and device for modifying a synthesis of a time-domain excitation decoded by a time-domain decoder, wherein the synthesis of the decoded time-domain excitation is classified into one of a number of categories. The decoded time-domain excitation is converted into a frequency-domain excitation, and the frequency-domain excitation is modified as a function of the category in which the synthesis of the decoded time-domain excitation is classified. The modified frequency-domain excitation is converted into a modified time-domain excitation, and a synthesis filter is supplied with the modified time-domain excitation to produce a modified synthesis of the decoded time-domain excitation.

Claims

1. A device for modifying a synthesis of a time-domain code-excited linear prediction (CELP) excitation decoded by a time-domain CELP decoder, comprising:

at least one processor; and

a memory coupled to the processor and comprising non-transitory instructions that when executed cause the processor to implement;

a classifier of the synthesis of the decoded time-domain CELP excitation into one of a number of categories;

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

a modifier of the frequency-domain excitation as a function of the category in which the synthesis of the decoded time-domain CELP excitation is classified by the classifier;

a second converter of the modified frequency-domain excitation into a modified time-domain CELP excitation; and

a first linear prediction synthesis filter supplied with the modified time-domain CELP excitation to produce a modified synthesis of the decoded time-domain CELP excitation.

2. A device for modifying a synthesis of a time-domain CELP excitation according to claim 1, wherein the modifier comprises:

a first calculator of a cut-off frequency where a time-domain excitation contribution stops to be used.

3. A device for modifying a synthesis of a time-domain CELP excitation according to claim 2, wherein the modifier comprises:

a zeroer of the frequency-domain excitation above the cut-off frequency; and

a normalizer of the frequency-domain excitation below the cut-off frequency to produce a normalized frequency-domain excitation.

4. A device for modifying a synthesis of a time-domain CELP excitation according to claim 3, wherein the modifier comprises:

a random noise generator; and

an adder of the random noise to the normalized frequency-domain excitation.

5. A device for modifying a synthesis of a time-domain CELP excitation according to claim 3, wherein the modifier comprises:

a second calculator of a matching gain using an energy of the frequency-domain excitation before and after modification, the second calculator applying the matching gain to the normalized frequency-domain excitation to produce the modified frequency-domain excitation.

6. A device for modifying a synthesis of a time-domain CELP excitation according to claim 2, wherein the classifier classifies the synthesis of the decoded time-domain CELP excitation as inactive or active unvoiced.

7. A device for modifying a synthesis of a time-domain CELP excitation according to claim 1, wherein the memory comprises non-transitory instructions that when executed cause the processor to implement:

a smoother of the first linear prediction synthesis filter when the synthesis of the decoded time-domain CELP excitation is classified as a given one of the categories by the classifier.

8. A device for modifying a synthesis of a time-domain CELP excitation according to claim 1, wherein the frequency-domain excitation is divided into frequency bands each divided into frequency bins, and wherein the modifier comprises:

a normalizer of the frequency-domain excitation using a frequency band-varying normalization factor to produce a normalized frequency-domain excitation.

9. A device for modifying a synthesis of a time-domain CELP excitation according to claim 8, wherein the normalizer comprises:

a zeroer of the frequency bins below a fraction of a maximum value of the normalized frequency-domain excitation in the frequency band comprising the frequency bins.

10. A device for modifying a synthesis of a time-domain CELP excitation according to claim 8, wherein the modifier comprises:

a first calculator of a matching gain per frequency band using an energy of the frequency-domain excitation before and after modification.

11. A device for modifying a synthesis of a time-domain CELP excitation according to claim 10, wherein the modifier comprises, for the frequency bands below a first frequency:

a second calculator for applying the matching gain to the normalized frequency-domain excitation to produce the modified frequency-domain excitation.

12. A device for modifying a synthesis of a time-domain CELP excitation according to claim 10, wherein, for the frequency bands between a first lower frequency and a second higher frequency, the memory comprises non-transitory instructions that when executed cause the processor to implement:

a finder of a maximum value per frequency band of the normalized frequency-domain excitation;

an amplifier for amplifying the matching gain by an amplification factor per frequency bin when the normalized frequency-domain excitation in the frequency bin is equal to or higher than a value proportional to said maximum value of the frequency band; and

a second calculator for applying the amplified matching gain to the normalized frequency-domain excitation in the frequency bin to produce in said frequency bin the modified frequency-domain excitation.

13. A device for modifying a synthesis of a time-domain CELP excitation according to claim 10, wherein, for the frequency bands between a first lower frequency and a second higher frequency, the memory comprises non-transitory instructions that when executed cause the processor to implement:

a finder of a maximum value per frequency band of the normalized frequency-domain excitation;

an attenuator for attenuating the matching gain by an attenuation factor per frequency bin of the frequency band when the normalized frequency-domain excitation in the frequency bin is lower than a value proportional to said maximum value of the frequency band; and

a second calculator for applying the attenuated matching gain to the normalized frequency-domain excitation in said frequency bin to produce in said frequency bin the modified frequency-domain excitation.

14. A device for modifying a synthesis of a time-domain CELP excitation according to claim 10, wherein, for the frequency bands above a given frequency, the memory comprises non-transitory instructions that when executed cause the processor to implement:

a finder of a maximum value per frequency band of the normalized frequency-domain excitation;

a second calculator of a tilt for the matching gain when the normalized frequency-domain excitation in the frequency bin is higher than a value proportional to said maximum value of the frequency band, the second calculator applying the calculated tilt to the matching gain; and

a third calculator for applying the matching gain to which the calculated tilt has been applied to the normalized frequency-domain excitation in said frequency bin to produce in said frequency bin the modified frequency-domain excitation.

15. A device for modifying a synthesis of a time-domain CELP excitation according to claim 10, wherein, for the frequency bands above a given frequency, the memory comprises non-transitory instructions that when executed cause the processor to implement:

a finder of a maximum value per frequency band of the normalized frequency-domain excitation;

an attenuator for attenuating the matching gain by an amplification factor per frequency bin of the frequency band when the normalized frequency-domain excitation in the frequency bin is lower than a value proportional to the maximum value of the frequency band; and

a second calculator for applying the attenuated matching gain to the normalized frequency-domain excitation in said frequency bin to produce in said frequency bin the modified frequency-domain excitation.

16. A device for decoding a sound signal encoded by encoding parameters, comprising:

a decoder of a time-domain CELP excitation in response to the sound signal encoding parameters;

a second synthesis filter responsive to the decoded time-domain CELP excitation to produce a synthesis of said time-domain CELP excitation; and

a device according to claim 1, for modifying the synthesis of the time-domain CELP excitation.

17. A method for modifying a synthesis of a time-domain code-excited linear prediction (CELP) excitation decoded by a time-domain CELP decoder, comprising:

classifying the synthesis of the decoded time-domain CELP excitation into one of a number of categories;

converting the decoded time-domain CELP excitation into a frequency-domain excitation;

modifying the frequency-domain excitation as a function of the category in which the synthesis of the decoded time-domain CELP excitation is classified;

converting the modified frequency-domain excitation into a modified time-domain CELP excitation;

synthesizing, using a linear prediction synthesis filter, the modified time-domain CELP excitation to produce a modified synthesis of the decoded time-domain CELP excitation.

18. A method for modifying a synthesis of a time-domain CELP excitation according to claim 17, wherein modifying the frequency-domain excitation comprises:

calculating a cut-off frequency where a time-domain excitation contribution stops to be used.

19. A method for modifying a synthesis of a time-domain CELP excitation according to claim 18, wherein modifying the frequency-domain excitation comprises:

zeroing the frequency-domain excitation above the cut-off frequency; and

normalizing the frequency-domain excitation below the cut-off frequency to produce a normalized frequency-domain excitation.

20. A method for modifying a synthesis of a time-domain CELP excitation according to claim 19, wherein modifying the frequency-domain excitation comprises generating a random noise and adding the random noise to the normalized frequency-domain excitation.

21. A method for modifying a synthesis of a time-domain CELP excitation according to claim 19, wherein modifying the frequency-domain excitation comprises:

calculating a matching gain using an energy of the frequency-domain excitation before and after modification, and applying the matching gain to the normalized frequency-domain excitation to produce the modified frequency-domain excitation.

22. A method for modifying a synthesis of a time-domain CELP excitation according to claim 18, wherein the synthesis of the decoded time-domain CELP excitation is classified as inactive or active unvoiced.

23. A method for modifying a synthesis of a time-domain CELP excitation according to claim 17, comprising smoothing the linear prediction synthesis filter performing the synthesis of the modified time-domain CELP excitation when the synthesis of the decoded time-domain CELP excitation is classified as a given one of the categories by a classifier.

24. A method for modifying a synthesis of a time-domain excitation according to claim 17, wherein the frequency-domain excitation is divided into frequency bands each divided into frequency bins, and wherein modifying the frequency-domain excitation comprises:

normalizing the frequency-domain excitation using a frequency band-varying normalization factor to produce a normalized frequency-domain excitation.

25. A method for modifying a synthesis of a time-domain CELP excitation according to claim 24, wherein modifying the frequency-domain excitation comprises zeroing the frequency bins below a fraction of a maximum value of the normalized frequency-domain excitation in the frequency band comprising the frequency bins.

26. A method for modifying a synthesis of a time-domain CELP excitation according to claim 24, wherein modifying the frequency-domain excitation comprises:

calculating a matching gain per frequency band using an energy of the frequency-domain excitation before and after modification.

27. A method for modifying a synthesis of a time-domain CELP excitation according to claim 26, wherein modifying the frequency-domain excitation comprises, for the frequency bands below a first frequency, applying the matching gain to the normalized frequency-domain excitation to produce the modified frequency-domain excitation.

28. A method for modifying a synthesis of a time-domain CELP excitation according to claim 26, comprising, for the frequency bands between a first lower frequency and a second higher frequency:

finding a maximum value per frequency band of the normalized frequency-domain excitation;

amplifying the matching gain by an amplification factor per frequency bin when the normalized frequency-domain excitation in the frequency bin is equal to or higher than a value proportional to said maximum value of the frequency band; and

applying the amplified matching gain to the normalized frequency-domain excitation in the frequency bin to produce in said frequency bin the modified frequency-domain excitation.

29. A method for modifying a synthesis of a time-domain CELP excitation according to claim 26, comprising, for the frequency bands between a first lower frequency and a second higher frequency:

finding a maximum value per frequency band of the normalized frequency-domain excitation;

attenuating the matching gain by an attenuation factor per frequency bin of the frequency band when the normalized frequency-domain excitation in the frequency bin is lower than a value proportional to said maximum value of the frequency band; and

applying the attenuated matching gain to the normalized frequency-domain excitation in said frequency bin to produce in said frequency bin the modified frequency-domain excitation.

30. A method for modifying a synthesis of a time-domain CELP excitation according to claim 26, comprising, for the frequency bands above a given frequency:

finding a maximum value per frequency band of the normalized frequency-domain excitation;

calculating a tilt for the matching gain when the normalized frequency-domain excitation in the frequency bin is higher than a value proportional to said maximum value of the frequency band, and applying the calculated tilt to the matching gain; and

applying the matching gain to which the calculated tilt has been applied to the normalized frequency-domain excitation in said frequency bin to produce in said frequency bin the modified frequency-domain excitation.

31. A method for modifying a synthesis of a time-domain excitation according to claim 26, comprising, for the frequency bands above a given frequency:

finding a maximum value per frequency band of the normalized frequency-domain excitation;

attenuating the matching gain by an amplification factor per frequency bin of the frequency band when the normalized frequency-domain excitation in the frequency bin is lower than a value proportional to the maximum value of the frequency band; and

applying the attenuated matching gain to the normalized frequency-domain excitation in said frequency bin to produce in said frequency bin the modified frequency-domain excitation.

32. A method for decoding a sound signal encoded by encoding parameters, comprising:

decoding a time-domain CELP excitation in response to the sound signal encoding parameters;

synthesizing the decoded time-domain CELP excitation to produce a synthesis of said time-domain CELP excitation; and

a method according to claim 17, for modifying the synthesis of the time-domain CELP excitation.