US3975587A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Digital vocoder
Assignee: ITT Inc
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Filing: 1974-09-13
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Granted: 1976-08-17
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Expires: 1994-09-13
Abstract
Abstract This invention relates to a digital vocoder where speech is translated to a digital version thereof. An adaptive filter in the form of an N stage Itakura type cascade derives from the speech a prediction residual and N spectral parameter in the form of weighting coefficients of the filter. The pitch period, derived from the prediction residual, the voiced/unvoiced decision derived from the first of the weighting coefficients and the peak amplitude of a pitch pulse, and a digital signal representing filter gain, derived from the last of the weighting coefficients are multiplexed with each other and the N spectral parameters for transmission to a receiver. The receiver employs an excitation generator responsive to the pitch period, the gain signal and the voiced/unvoiced decision to produce an excitation signal to excite an N/2 cascade connected stage receive filter. Each stage of the receive filter operates on a time shared basis on an adjacent pair of the N spectral parameters. The receive adaptive filter operation is the inverse of the transmit adaptive filter so that after digital to analog conversion the original speech is substantially reproduced.
Inventors
- 👤 James Grant Dunn
- 👤 John Richard Cowan
- 👤 Anthony Joseph Russo
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 13:07
CPC Classifications
G; G10; G10L; G10L19/00; G10L19/04; G10L19/08; G10L25/00; G10L25/93
Claims Analysis
Total Claims: 25
Claim 1
Independent Claim
325 words
A digital vocoder comprising: a transmitter including a source of speech, an analog to digital converter coupled to said source to provide a first digital representation of said speech, an adaptive filter coupled to said analog to digital converter to derive from said first digital representation of said speech a digital prediction residual signal and digital spectral parameters, a pitch period extraction circuit coupled to one output of said adaptive filter responsive to said residual signal to produce a first digital excitaion signal representing the pitch period of said speech, a voiced/unvoiced decision circuit coupled to said adaptive filter and said pitch period extraction circuit to produce a second digital excitation signal indicating when said speech is voiced and when said speech is unvoiced, an arrangement coupled to another output of said adaptive filter to produce a digital number representing the gain of said adaptive filter, and a multiplexing and transmitting arrangement coupled to said adaptive filter, said pitch period extraction circuit and said voiced/unvoiced decision circuit to time multiplex and transmit said digital spectral parameters, said first and second digital excitation signals and said digital number; and a receiver including a receiving and demultiplexing arrangement coupled to said multiplexing and transmitting arrangement to receive and separate from each other said digital spectral parameters, said first and second digital excitation signals and said digital number, an excitation generator coupled to said receiving and demultiplexing arrangement responsive to said first and second digital excitation signals and said digital number to produce a third digital excitation signal. a receive filter coupled to said excitation generator and said receiving and demultiplexing arrangement responsive to said digital spectral parameters and said third excitation signal to provide a second digital representation of said speech which is substantially identical to said first digital representation of said speech, and a digital to analog converter coupled to said receive filter to provide a speech output substantially identical to said speech of said source.
Claim 2
Dependent Claim
325 words
A digital vocoder comprising: a transmitter including a source of speech, an analog to digital converter coupled to said source to provide a first digital representation of said speech, an adaptive filter coupled to said analog to digital converter to derive from said first digital representation of said speech a digital prediction residual signal and digital spectral parameters, a pitch period extraction circuit coupled to one output of said adaptive filter responsive to said residual signal to produce a first digital excitaion signal representing the pitch period of said speech, a voiced/unvoiced decision circuit coupled to said adaptive filter and said pitch period extraction circuit to produce a second digital excitation signal indicating when said speech is voiced and when said speech is unvoiced, an arrangement coupled to another output of said adaptive filter to produce a digital number representing the gain of said adaptive filter, and a multiplexing and transmitting arrangement coupled to said adaptive filter, said pitch period extraction circuit and said voiced/unvoiced decision circuit to time multiplex and transmit said digital spectral parameters, said first and second digital excitation signals and said digital number; and a receiver including a receiving and demultiplexing arrangement coupled to said multiplexing and transmitting arrangement to receive and separate from each other said digital spectral parameters, said first and second digital excitation signals and said digital number, an excitation generator coupled to said receiving and demultiplexing arrangement responsive to said first and second digital excitation signals and said digital number to produce a third digital excitation signal. a receive filter coupled to said excitation generator and said receiving and demultiplexing arrangement responsive to said digital spectral parameters and said third excitation signal to provide a second digital representation of said speech which is substantially identical to said first digital representation of said speech, and a digital to analog converter coupled to said receive filter to provide a speech output substantially identical to said speech of said source.
Claim 3
Dependent Claim
33 words
A vocoder according to claim 1, wherein said digital spectral parameters are N digital signals each representing a different weighting coefficient of said adaptive filter, where N is an integer greater than 1.
Claim 4
Dependent Claim
18 words
A vocoder according to claim 2, wherein said adaptive filter includes N stages of an Itakura type cascade.
Claim 5
Dependent Claim
84 words
A vocoder according to claim 3, wherein each of said stages includes a residual calculator providing a forward residual output and a backward residual output, and a correlation calculator coupled to the input of said residual calculator to operate on said forward and backward residual outputs of the previous one of said residual calculators; and a divide circuit having inputs coupled to the outputs of said correlation calculator and an output coupled to said residual calculator and said divide circuit provides said weighting coefficient.
Claim 6
Dependent Claim
28 words
A vocoder according to claim 4, wherein each of said residual calculators, each of said correlation calculators and said divide circuits include a repetitive serial arithmetic logic units.
Claim 7
Dependent Claim
89 words
A vocoder according to claim 5, wherein said receive filter includes N/2 logic stages connected in cascade with respect to each other and said third excitation signal with a first feedback arrangement between adjacent ones of said stages and a pair of feedback arrangement in each of said stages, each of said N/2 logic stages being coupled to said receiving and demultiplexing arrangement to operate on a different adjacent pair of said N weighting coefficients on a time sharing basis to provide said second digital representation of said speech.
Claim 8
Dependent Claim
19 words
A vocoder according to claim 6, wherein each of said N/2 logic stages include repetitive serial arithmetic logic units.
Claim 9
Dependent Claim
73 words
A vocoder according to claim 1, wherein said transmitter further includes a linear to log code converter coupled between said arrangement and said multiplexing and transmitting arrangement to convert said digital number to a log code representing said gain; and said receiver further includes a log to linear code converter coupled between said receiving and demultiplexing arrangement and said excitation generator to convert said log code to a linear code representing said gain.
Claim 10
Dependent Claim
49 words
A vocoder according to claim 1, further including a pitch period correction circuit coupled to said pitch period extraction circuit and said voiced/unvoiced decision circuit to eliminate any large changes in said pitch period and thereby improve the quality of said speech output of said digital to analog converter.
Claim 11
Dependent Claim
169 words
A transmitter for a digital vocoder comprising: an analog to digital converter coupled to a source of speech to provide a digital representation of said speech; an adaptive filter coupled to said converter to derive from said digital representation of said speech a digital prediction residual and digital spectral parameters; a pitch period extraction circuit coupled to one output of said filter responsive to said residual signal to produce a first digital signal representing the pitch period of said speech; a voiced/unvoiced decision circuit coupled to said filter and said extraction circuit to produce a second digital excitation signal indicating when said speech is voiced and when said speech is unvoiced; an arrangement coupled to another output of said filter to produce a digital number representing the gain of said adaptive filter; and a multiplexing and transmitting arrangement coupled to said filter, said extraction circuit and said decision circuit to time multiplex and transmit said digital spectral parameters, said first and second digital excitation signals and said digital number.
Claim 12
Dependent Claim
169 words
A transmitter for a digital vocoder comprising: an analog to digital converter coupled to a source of speech to provide a digital representation of said speech; an adaptive filter coupled to said converter to derive from said digital representation of said speech a digital prediction residual and digital spectral parameters; a pitch period extraction circuit coupled to one output of said filter responsive to said residual signal to produce a first digital signal representing the pitch period of said speech; a voiced/unvoiced decision circuit coupled to said filter and said extraction circuit to produce a second digital excitation signal indicating when said speech is voiced and when said speech is unvoiced; an arrangement coupled to another output of said filter to produce a digital number representing the gain of said adaptive filter; and a multiplexing and transmitting arrangement coupled to said filter, said extraction circuit and said decision circuit to time multiplex and transmit said digital spectral parameters, said first and second digital excitation signals and said digital number.
Claim 13
Dependent Claim
32 words
A transmitter according to claim 10, wherein said digital spectral parameters are N digital signals each representing a different weighting coefficient of said filter, where N is an integer greater than 1.
Claim 14
Dependent Claim
17 words
A transmitter according to claim 11, wherein said filter includes N stages of an Itakura type cascade.
Claim 15
Dependent Claim
84 words
A transmitter according to claim 12, wherein each of said stages include a residual calculator providing a forward residual output and a backward residual output, and a correlation calculator coupled to the input of said residual calculator to operate on said forward and backward residual outputs of the previous one of said residual calculators; and a divide circuit having inputs coupled to the outputs of said correlation calculator and an output coupled to said residual calculator and said divide circuit provides said weighting coefficient.
Claim 16
Dependent Claim
29 words
A transmitter according to claim 13, wherein each of said residual calculators, each of said correlation calculators and each of said divide circuits include repetitive serial arithmetic logic units.
Claim 17
Dependent Claim
39 words
A transmitter according to claim 10, wherein said transmitter further includes a linear to log code converter coupled between said arrangement and said multiplexing and transmitting arrangement to convert said digital number to a log code representing said gain.
Claim 18
Dependent Claim
49 words
A transmitter according to claim 10, further including a pitch period correction circuit coupled to said pitch period extraction circuit and said voiced/unvoiced decision circuit to eliminate any large changes in said pitch period and thereby improve the quality of said speech output of said digital to analog converter.
Claim 19
Dependent Claim
145 words
A receiver for a digital vocoder comprising: a receiving and demultiplexing arrangement to receive a serial digital pulse train containing digital spectral parameters derived in an adaptive filter at a transmitter from input speech, first and second digital excitation signals derived at said transmitter from said adaptive filter and a log coded digital number representing gain in said adaptive filter and to separate the contents of said pulse train; an excitation generator coupled to said arrangement responsive to said first and second excitation signals and said digital number to produce a third excitation signal; a receive filter coupled to said generator and said arrangement responsive to said digital spectral parameters and said third excitation signal to provide a digital representation of speech; and a digital to analog converter coupled to said filter to provide a speech output which is substantially identical to said input speech.
Claim 20
Dependent Claim
145 words
A receiver for a digital vocoder comprising: a receiving and demultiplexing arrangement to receive a serial digital pulse train containing digital spectral parameters derived in an adaptive filter at a transmitter from input speech, first and second digital excitation signals derived at said transmitter from said adaptive filter and a log coded digital number representing gain in said adaptive filter and to separate the contents of said pulse train; an excitation generator coupled to said arrangement responsive to said first and second excitation signals and said digital number to produce a third excitation signal; a receive filter coupled to said generator and said arrangement responsive to said digital spectral parameters and said third excitation signal to provide a digital representation of speech; and a digital to analog converter coupled to said filter to provide a speech output which is substantially identical to said input speech.
Claim 21
Dependent Claim
33 words
A receiver according to claim 17, wherein said digital spectral parameters are N digital signals each representing a different weighting coefficient of said adaptive filter, where N is an integer greater than 1.
Claim 22
Dependent Claim
87 words
A receiver according to claim 18, wherein said receive filter includes N/2 logic stages connected in cascade with respect to each other and said third excitation signal with a first feedback arrangement between adjacent ones of said stages and a pair of feedback arrangement in each of said stages, each of said N/2 logic stages being coupled to said receiving and demultiplexing arrangement to operate on a different adjacent pair of said N weighting coefficients on a time sharing basis to provide said digital representation of speech.
Claim 23
Dependent Claim
19 words
A receiver according to claim 19, wherein each of said N/2 logic stages include repetitive serial arithmetic logic units.
Claim 24
Dependent Claim
37 words
A receiver according to claim 20, wherein said receiver filter further includes a log to linear code converter coupled between said arrangement and said generator to convert said digital number to a linear code representing said gain.
Claim 25
Dependent Claim
37 words
A receiver according to claim 17, wherein said receiver filter further includes a log to linear code converter coupled between said arrangement and said generator to convert said digital number to a linear code representing said gain.
References Cited (Backward Citations)
US3327058A
Cited
US3471648A
Cited
US3631520A
Cited
US3624302A
Cited
US3750024A
Cited
US3746791A
Cited
US3715512A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1979-08-17 | 1980-02-16 | 1980-08-17 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1983-08-17 | 1984-02-16 | 1984-08-17 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1987-08-17 | 1988-02-16 | 1988-08-17 | $7700.00 | Window Closed / Lapsed |