Digital voice compression having a digitally controlled AGC circuit and means for including the true gain in the compressed data

• US 4,611,342 A
• Filed: 03/01/1983
• Issued: 09/09/1986
• Est. Priority Date: 03/01/1983
• Status: Expired due to Term

• Current Assignee: Racal-Datacom, Inc. (Thales SA)
• Original Assignee: Racal Data Communications Incorporated
• Inventors: Miller, William J., Joerger, Richard B., Newdeck, Frank W., Chiu, Ran F.
• Primary Examiner(s): Shaw, Gareth D.
• Assistant Examiner(s): Salotto, John J.
• Application Number:
  US06/471,139
• Time in Patent Office: 1,288 Days
• Field of Search: 381/29-40, 381/40-53, 179/175.31 E, 179/170.2, 179/170.4, 179/170.6, 179/170.8, 179/175.31 E, 340/347 AD, 340/347 M, 367/65-67, 364/513, 364/513.5
• US Class Current: 704/225
• CPC Class Codes: G10L 19/04 using predictive techniques
• CPC Class Codes: G10L 21/00 Speech or voice signal processing techniques to produce another audible or non-audible signal, e.g. visual or tactile, in order to modify its quality or its intelligibility G10L19/00 takes precedence
• CPC Class Codes: H03G 3/30 in amplifiers having semiconductor devices
• CPC Class Codes: H03G 7/007 of digital or coded signals

Abstract

An apparatus for use in transmitting compressed digital voice data includes an analyzer for compressing digitized voice data according to an algorithm which produces a root mean square of the voice data. An analog to digital converter is used to convert analog voice signals to digital data as an input to the analyzer. An AGC circuit controls to analog voice signal to keep it within predetermined limits for digitization, with the AGC setting being determined by the root mean square of the digitized data. The digitized data includes data representative of the root mean square adjusted by the inverse of the change induced by the AGC. A speech synthesizer expands the digitized data at a remote location to convert it back to analog speech signals.

Claims

1. An apparatus for use in the transmission of digital voice data, comprising a digital voice processor including:

an analyzer means for compressing digitized voice data according to an algorithm including a measured root mean square of the digitized voice data being compressed;

an analog-to-digital conversion means for converting an analog voice signal to digitized voice data as an input to the analyzer means;

an automatic gain control means within the analog-to-digital conversion means for controlling the gain of the analog voice signal prior to the analog voice signal being digitized, such that the digitized voice data input to the analyzer means has a root mean square within selected limits, the setting of the automatic gain control means being responsive to the value of the root mean square of the digitized voice data, as measured by the analyzer means;

means for including in the digitized voice data, compressed for transmission, data representative of the root mean measured in the analyzer means, adjusted by the inverse of the change induced in the gain of the automatic gain control means in order to maintain the analyzer means root mean square within the selected limits;

the automatic gain control means including a gain setting means for setting the gain in a stepwise fashion, with each step constituting a change in the gain of a selected value from the previous gain setting, in response to a digital output gain signal;

an output gain signal selection means for selecting the digital output gain signal in response to the relation between the most recent peak root mean square measured by the analyzer and a selected ideal root mean square value plus or minus a selected range value; and

, a voice synthesizer means receiving said output gain signal for generating a synthesized voice signal.

2. The apparatus of claim 1, further comprising:

the output gain signal selection means including a stored memory containing values representative of selected desired gain settings and the output gain signal selection means selecting the desired gain setting from the stored memory.

3. The apparatus of claim 1 further comprising:

the analyzer means including a means for determining the existence of voiced and unvoiced components of the digitized voice data to be compressed for transmission; and

,

the automatic gain control means including a limiting means for limiting rapid gain changes and insuring gain changes are in response to changes in the voiced component of the digitized voice data, the limiting means including a means for detecting a voiced component or an unvoiced component in the digitized voice data, compressed for transmission, and assigning a posivite value to each occurrence of a voiced component, and a negative value to each occurrence of an unvoiced component, and for initiating a gain change in response to the cumulative sum of the positive and negative values, exceeding a selected value.

4. The apparatus of claim 3, further comprising:

the output gain signal selection means including a stored memory containing values representative of selected desired gain settings and the output gain signal selection means selecting the desired gain setting from the stored memory.

5. A sythesizer for simulating speech by producing an analog speech signal from digitized voice data, compressed for transmission by an analyzer means at a remote location, wherein the compressed digitized voice data is arranged in frames and includes data representative of pitch, gain, and a plurality of linear predictive algorithm envelope generation factors for each frame, comprising:

adjustable filtering means responsive to said envelope generation factors for generating the frequency domain envelope of the speech signal from the envelope generation factors according to a linear predictive algorithm;

a harmonic generating means for coupled to said adjustable filtering means for generating harmonics of the pitch having amplitudes as defined by the frequency domain envelope;

an amplifying means for amplifying the output of the harmonic generating means in response to the gain data representative of the actual gain of the voice signal, which gain data is representative of the root means square, detected in the analyzer at the remote location, adjusted by the inverse of the gain change induced in the analog voice signal, prior to compression at the remote location, in order to maintain the root mean square of the remote analyzer within selected limits; and

an echo suppression means, responsive to said analyzer root mean square and responsive to a synthesizer root means square, for detecting which of the digitized voice signals in the analyzer or the sythesizer has a lesser root means square and for suppressing the gain of the one detected to have the lesser root mean square.

6. The apparatus of claim 5, further comprising:

a synthesizer gain suppressing means for detecting whether the most recent peak root mean square in the analyzer is greater than a first selected threshold and is greater than the root mean square in the synthesizer plus a selected loss compensation value, and for suppressing the gain in the synthesizer responsive to the detection of such a condition;

an analyzer gain suppressing means for detecting whether the most recent peak root mean square in the synthesizer is greater than the first selected threshold and is greater than the root mean square in the analyzer plus the selected loss compensation value, and for suppressing the gain in the analyzer responsive to the detection of such a condition; and

said synthesizer and analyzer suppressing means both responsive to said analyzer and synthesizer root mean squares.

7. The apparatus of claim 6, further comprising:

a near talker interrupt detection means for detecting whether the root mean square in the analyzer exceeds a second selected threshold and for removing the suppression of the analyzer gain in response to the existence of such a condition;

a far talker interrupt detection means for detecting whether the root mean square in the synthesizer exceeds the second selected threshold and for removing the suppression of the synthesizer gain in response to the existence of such a condition; and

said near and far talker interrupt detection means both responsive to said analyzer and synthesizer root mean squares.

8. An apparatus for use in the transmission of digital voice data, compressed for transmission, comprising:

an analyzer means for compressing digitized voice data according to an algorithm including a measured root mean square of the digitized voice data being compressed;

an analog-to-digital conversion means for converting an analog voice signal to digitized voice data as an input to the analyzer means;

an automatic gain control means within the analog-to-digital conversion means for controlling the gain of the analog voice signal prior to the analog voice signal being digitized, such that the digitized voice data input to the analyzer means has a root mean square within selected limits, the setting of the automatic gain control means being responsive to the value of the root mean square of the digitized voice data, as measured by the analyzer means;

means for including in the digitized voice data, compressed for transmission, data representative of the root mean square measured in the analyzer means, adjusted by the inverse of the change induced in the gain of the automatic gain control means in order to maintain the analyzer means root mean square within the selected limits;

the automatic gain control means including a gain setting means for setting the gain in a stepwise fashion, with each step constituting a change in the gain of a selected value from the previous gain setting, in response to a digital output gain signal; and

,

an output gain signal selection means for selecting the digital output gain signal in response to the relation between the most recent peak root mean square measured by the analyzer and a selected ideal root mean square value plus or minus a selected range value.

9. The apparatus of claim 8, further comprising:

the output gain signal selection means including a stored memory containing values representative of selected desired gain settings and the output gain signal selection means selects the desired gain setting from the stored memory.

10. The apparatus of claim 8, further comprising:

the analyzer means including a means for determining the existence of voiced and unvoiced components of the digitized voice data to be compressed for transmission; and

,

the automatic gain control means including a limiting means for limiting rapid gain changes and insuring gain changes are in response to changes in the voiced component of the digitized voice data, the limiting means including a means for detecting a voiced component or an unvoiced component in the digitized voice data, compressed for transmission, and assigning a positive value to each occurrence of a voiced component, and a negative value to each occurrence of an unvoiced component, and for initiating a gain change in response to the cumulative sum of the positive and negative values, exceeding a selected value.

11. The apparatus of claim 10, further comprising:

the output gain signal selection means including a stored memory containing values representative of selected desired gain settings and the output gain signal selection means selecting the desired gain setting from the stored memory.

12. An apparatus for use in the transmission of digital voice data, compressed for transmission, comprising:

an analyzer means for compressing digitized voice data according to an algorithm including a measured root mean square of the digitized voice data being compressed;

an analog-to-digital conversion means for converting an analog voice signal to digitized voice data as an input to the analyzer means;

an automatic gain control means within the analog-to-digital conversion means for controlling the gain of the analog voice signal prior to the analog voice signal being digitized, such that the digitized voice data input to the analyzer means has a root mean square within selected limits, the setting of the automatic gain control means being responsive to the value of the root mean square of the digitized voice data, as measured by the analyzer means;

means for including in the digitized voice data, compressed for transmission, data representative of the root mean square measured in the analyzer means, adjusted by the inverse of the change induced in the gain of the automatic gain control means in order to maintain the analyzer means root mean square within the selected limits;

the analyzer means including a means for determining the existence of voiced and unvoiced components of the digitized voice data to be compressed for transmission; and

,

the automatic gain control means including a limiting means for limiting rapid gain changes and insuring gain changes are in response to changes in the voiced component of the digitized voice data, the limiting means including a means for detecting a voiced component or an unvoiced component in the digitized voice data, compressed for transmission, and assigning a positive value to each occurrence of a voiced component, and a negative value to each occurrence of an unvoiced component, and for initiating a gain change in response to the cumulative sum of the positive and negative values, exceeding a selected value.

13. The apparatus of claim 12, further comprising:

the output gain signal selection means including a stored memory containing values representative of selected desired gain settings and the output gain signal selection means selecting the desired gain setting from the stored memory.

14. An apparatus for use in the transmission of digital voice data, compressed for transmission, comprising:

an analyzer means for compressing digitized voice data according to an algorithm including a measured root mean square of the digitized voice data being compressed;

an analog-to-digital conversion means for converting an analog voice signal to digitized voice data as an input to the analyzer means;

an automatic gain control means within the analog-to-digital conversion means for controlling the gain of the analog voice signal prior to the analog voice signal being digitized, such that the digitized voice data input to the analyzer means has a root mean square within selected limits, the setting of the automatic gain control means being responsive to the value of the root mean square of the digitized voice data, as measured by the analyzer means;

means for including in the digitized voice data, compressed for transmission, data representative of the root mean square measured in the analyzer means, adjusted by the inverse of the change induced in the gain of the automatic gain control means in order to maintain the analyzer means root mean square within the selected limits; and

a synthesizer means for synthesizing expanded digitized voice data, received from a remote location as compressed digitized voice data, to form an analog speech signal.

15. The apparatus of claim 14, further comprising:

an echo suppression means responsive to the root mean squares from said synthesizer and said analyzer for detecting which of the digitized voice signals in the analyzer of the synthesizer has a lesser root mean square and for suppressing the gain of the one detected to have the lesser root mean square.

16. The apparatus of claim 15, further comprising:

a synthesizer gain suppressing means for detecting whether the most recent peak root mean square in the analyzer is greater than a first selected threshold and is greater than the root mean square in the synthesizer plus a selected loss compensation value, and for suppressing the gain in the synthesizer responsive to the detection of such a condition;

an analyzer gain suppressing means for detecting whether the most recent peak root mean square in the synthesizer is greater than the first selected threshold and is greater than the root mean square in the analyzer plus the selected loss compensation value, and for suppressing the gain in the analyzer responsive to the detection of such a condition; and

said synthesizer and analyzer suppressing means both responsive to said analyzer and synthesizer root mean squares.

17. The apparatus of claim 16, further comprising:

a near talker interrupt detection means for detecting whether the root mean square in the analyzer exceeds a second selected threshold and for removing the suppression of the analyzer gain in response to the existence of such a condition;

a far talker interrupt detection means for detecting whether the root mean square in the synthesizer exceeds the second selected threshold and for removing the suppression of the synthesizer gain in response to the existence of such a condition; and

said near and far talker interrupt detection means both responsive to said analyzer and synthesizer root mean squares.

18. An apparatus for use in the transmission of digital voice data, compressed for transmission, comprising:

an analyzer means for compressing digitized voice data according to an algorithm including a measured root mean square of the digitized voice data being compressed;

an analog-to-digital conversion means for converting an analog voice signal to digitized voice data as an input to the analyzer means;

an automatic gain control means within the analog-to-digital conversion means for controlling the gain of the analog voice signal prior to the analog voice signal being digitized, such that the digitized voice data input to the analyzer means has a root means square within selected limits, the setting of the automatic gain control means being responsive to the value of the root mean square of the digitized voice data, as measured by the analyzer means;

means for including in the digitized voice data, compressed for transmission, data representative of the root mean square measured in the analyzer means, adjusted by the inverse of the change induced in the gain of the automatic gain control means in order to maintain the analyzer means root mean square within the selected limits;

a synthesizer means for synthesizing expanded digitized voice data, received from a remote location as compressed digitized voice data, to form an analog speech signal;

a synthesizer gain suppressing means, responsive to said synthesizer and analyzer root mean squares, for detecting whether the most recent peak root mean square in the analyzer is greater than a first selected threshold and is greater than the root mean square in the synthesizer plus a selected loss compensation value, and for suppressing the gain in the synthesizer responsive to the detection of such a condition; and

an analyzer gain suppressing means, responsive to said synthesizer and analyzer root mean squares, for detecting whether the most recent peak root mean square in the synthesizer is greater than the first selected threshold and is greater than the root mean square in the analyzer plus the selected loss compensation value, and for suppressing the gain in the analyzer responsive to the detection of such a condition.

19. The apparatus of claim 18, further comprising:

a near talker interrupt detection means for detecting whether the root mean square in the analyzer exceeds a second selected threshold and for removing the suppression of the analyzer gain in resppnse to the existence of such a condition;

a far talker interrupt detection means for detecting whether the root mean square in the synthesizer exceeds the second selected threshold and for removing the suppression of the synthesizer gain in response to the existence of such a condition; and

said near and far talker interrupt detection means both responsive to said analyzer and synthesizer root mean squares.

20. A method of compressing a digitized voice signal for transmission, comprising:

converting an analog voice signal to an expanded digitized voice signal;

compressing the digitized voice signal in an analyzer means for digitized voice compression according to an algorithm including a measured root mean square of the digitized voice signal;

dhanging the gain of the expanded digitized voice signal, as necessary, in order to maintain the root mean square within selected limits;

including in the digitized voice data compressed for transmission data representing the measured root mean square adjusted by the inverse of change in the gain of the expanded digitized voice data induced to maintain the root mean square within the selected limits; and

the changing step including detecting the voiced and unvoiced components of the digitized voice signal and assigning a positive value to the voiced components and a negative value to the unvoiced components and initiating a gain change in response to the sum of the positive and negative values exceeding a selected value and in response to the most recent peak root mean square differing from a selected ideal root mean square by a selected range value.