Constant data rate speech encoder for limited bandwidth path
First Claim
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1. A method for transmitting information with a fluctuating frequency spectrum over a limited-data-rate signal path, comprising the steps of:
- dividing said information into intervals;
providing memorized frequency spectra identifiable by codewords of the same bit size;
for each of said intervals, comparing the frequency spectrum of said information with said memorized frequency spectra, for selecting one of said codewords which represents that one memorized frequency spectrum which most closely represents the frequency spectrum of said information, to thereby form a selected codeword representative of a single interval;
for each of a first plurality of said intervals taken as a set, comparing said frequency spectrum of said information in said set with said memorized frequency spectra, for selecting one of said codewords which represents that one memorized frequency spectrum which most closely represents the frequency spectrum of said information in said first plurality of intervals taken as the set, to thereby form a selected codeword representative of first plural intervals;
placing at least some of said selected codewords in a first-in, first-out buffer;
reading said codewords from said buffer at a predetermined bit rate;
monitoring the ullage of said buffer, and, in said placing step, (a) tending to place in said buffer those of said selected codewords representative of plural intervals when said buffer tends to be full, and (b) tending to place in said buffer those of said selected codewords representative of a single interval when said buffer tends to be empty, whereby said buffer tends not to overflow or empty.
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Abstract
A speech signal has its characteristics extracted and encoded (16), transmitted over a limited-data-rate path (18) and is decoded (20) and synthesized (22) at the receiving end. The characteristics include line spectral frequencies (LSF), pitch and jitter. The LSF are extracted by autoregression, and split-vector quantized (SVQ) in a single frame, and, in parallel, in blocks of two, three and four frames. The SVQ codes have equal length and are evaluated for distortion in conjunction with a threshold. The threshold is varied in such a manner as tend to select for transmission those codewords which maintain a constant data rate into a transmit buffer. A single-bit jitter bit, and encoded pitch value, are product coded with the selected LSF codeword, and all are transmitted over the data path (18) to the receiver. The receiver decodes the characteristics, and controls a pitch generated (1226) in response to the pitch value and a random pitch jitter in response to the jitter bit. Two sets of line spectrum filters receive random noise and the pitch signal, respectively. The filtered signals are modulated by multipliers (1222, 1230) controlled by the LSF codes, and the filtered signals are summed and applied to a final LSF-controlled filter.
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Citations
17 Claims
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1. A method for transmitting information with a fluctuating frequency spectrum over a limited-data-rate signal path, comprising the steps of:
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dividing said information into intervals; providing memorized frequency spectra identifiable by codewords of the same bit size; for each of said intervals, comparing the frequency spectrum of said information with said memorized frequency spectra, for selecting one of said codewords which represents that one memorized frequency spectrum which most closely represents the frequency spectrum of said information, to thereby form a selected codeword representative of a single interval; for each of a first plurality of said intervals taken as a set, comparing said frequency spectrum of said information in said set with said memorized frequency spectra, for selecting one of said codewords which represents that one memorized frequency spectrum which most closely represents the frequency spectrum of said information in said first plurality of intervals taken as the set, to thereby form a selected codeword representative of first plural intervals; placing at least some of said selected codewords in a first-in, first-out buffer; reading said codewords from said buffer at a predetermined bit rate; monitoring the ullage of said buffer, and, in said placing step, (a) tending to place in said buffer those of said selected codewords representative of plural intervals when said buffer tends to be full, and (b) tending to place in said buffer those of said selected codewords representative of a single interval when said buffer tends to be empty, whereby said buffer tends not to overflow or empty. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A method for transmitting information with a fluctuating frequency spectrum over a limited-data-rate signal path, comprising the steps of:
- dividing said information into intervals;
providing memorized frequency spectra identifiable by codewords of the same bit size;for each of said intervals, comparing the frequency spectrum of said information with said memorized frequency spectra, for selecting one of said codewords which represents that one memorized frequency spectrum which most closely represents the frequency spectrum of said information, to thereby form a selected codeword representative of a single interval; for each of a number of said intervals taken as a set, which number is less than said first plurality of said intervals, comparing said frequency spectrum of said information in said set with said memorized frequency spectra, for selecting one of said codewords which represents that one memorized frequency spectrum which most closely represents said frequency spectrum of said information in said set, to thereby form a selected codeword representative of a number of intervals; placing at least some of said codewords in a buffer; reading codewords from said buffer at a predetermined rate onto said signal path; in conjunction with said placing step, choosing for placement in said buffer, from among said selected codewords, those codewords which, when placed in said buffer, result in an average data rate equal to said predetermined rate, and which, for said average data rate, provide the least distortion of said information. - View Dependent Claims (14, 15, 16, 17)
- dividing said information into intervals;
Specification
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Current AssigneeLockheed Martin Corporation (Martin Marietta Corporation)
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Original AssigneeLockheed Martin Corporation (Martin Marietta Corporation)
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InventorsNandkumar, Srinivas, Carmody, John Charles, Rothweiler, Joseph Harvey
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Primary Examiner(s)Safourek, Benedict V.
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Assistant Examiner(s)NGO, RICKY QUOC
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Application NumberUS08/486,130Time in Patent Office775 DaysField of Search395/2.09, 395/2.1, 395/2.14, 395/2.15, 395/2.16, 395/2.29, 395/2.3, 395/2.31, 395/2.32, 381/36, 381/37-42, 381/49, 381/50US Class Current704/222CPC Class CodesG10L 19/002 Dynamic bit allocation for ...G10L 19/022 Blocking, i.e. grouping of ...H03M 7/3082 Vector coding for televisio...
