Speech coding system and method including voicing cut off frequency analyzer
First Claim
1. A method of encoding a speech signal, said method comprising the steps of:
- obtaining at least one frame of said speech signal;
estimating a voicing cutoff frequency for said at least one frame of said speech signal, including the step of providing said at least one frame to a bandpass filter having outputs corresponding to eight voicing cutoff frequency bands represented by three voicing index signal bits, and filtering said at least one frame of said speech signal to determine a voicing cutoff frequency for said at least one frame of said speech signal, wherein each of said eight voicing frequency cutoff frequency bands corresponds to a voicing cutoff frequency value selected from the group comprising 0 Hz, 571 Hz, 1143 Hz, 1714 Hz, 2286 Hz, 2857 Hz, 3249 Hz, and 4000 Hz.
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Accused Products
Abstract
A speech coding system and associated method relies on a speech encoder (15) and a speech decoder (20). The speech encoder (15) includes a voicing cut off frequency analyzer (60). Voicing cut off frequency analyzer (60) includes voicing cut off frequency estimator (61) and voicing cut off frequency quantizer (62). Voicing cut off frequency estimator (61) estimates a voicing cut off frequency value for respective samples of an input speech waveform (1). To accomplish this, voicing cut off frequency estimator (61) utilizes a bandpass filter to estimate a frequency above which a sample of speech is voiced and below which the sample of speech is unvoiced. Voicing cut off frequency quantizer (62) quantizes the estimated voicing cut off frequency value and provides, for respective samples, a voicing cut off frequency index signal (6) which may be stored or transmitted. Voicing cut off frequency index signal (6) may comprise as few as 1 bit, and in a preferred embodiment, as few as 3 bits.
70 Citations
13 Claims
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1. A method of encoding a speech signal, said method comprising the steps of:
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obtaining at least one frame of said speech signal; estimating a voicing cutoff frequency for said at least one frame of said speech signal, including the step of providing said at least one frame to a bandpass filter having outputs corresponding to eight voicing cutoff frequency bands represented by three voicing index signal bits, and filtering said at least one frame of said speech signal to determine a voicing cutoff frequency for said at least one frame of said speech signal, wherein each of said eight voicing frequency cutoff frequency bands corresponds to a voicing cutoff frequency value selected from the group comprising 0 Hz, 571 Hz, 1143 Hz, 1714 Hz, 2286 Hz, 2857 Hz, 3249 Hz, and 4000 Hz.
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2. A method of encoding a speech signal, said method comprising the steps of:
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obtaining at least one frame of said speech signal; estimating a voicing cutoff frequency for said at least one frame of said speech signal; quantizing said voicing cutoff frequency to provide a voicing cutoff frequency index signal corresponding to said at least one frame, said voicing cutoff frequency index signal comprising one or more binary digits; storing said voicing cutoff frequency index signal in memory; and utilizing said voicing cutoff frequency value, including the step of generating harmonics to produce voiced excitation, the number of harmonics generated being determined according to the formula;
##EQU7## wherein;
nh is the number of harmonics generated,fsel is the integer representation of said voicing cutoff frequency index signal, and f0 is the fundamental frequency of said voiced portion of synthesized speech. - View Dependent Claims (3)
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4. A device including a voicing cutoff frequency analyzer, for encoding a speech signal, said voicing cutoff frequency analyzer comprising:
- a voicing cutoff frequency estimator adapted to receive respective frames of said speech signal and to determine a corresponding voicing cutoff frequency value for each of said respective frames, and to provide said voicing cutoff frequency value to an output port, said voicing cutoff frequency estimator comprising a bandpass filter means; and
a voicing cutoff frequency quantizer in communication with said output port of said voicing cutoff frequency estimator, said voicing cutoff frequency quantizer being adapted to receive said voicing cutoff frequency value at an input port and to provide a voicing cutoff frequency index signal at an output port; wherein said bandpass filter means comprises; a first band adapted to pass frequencies from about 0 Hz to about 570 Hz; a second band adapted to pass frequencies from about 571 Hz to about 1142 Hz; a third band adapted to pass frequencies from about 1143 Hz to about 1713 Hz; a fourth band adapted to pass frequencies from about 1714 Hz to about 2285 Hz; a fifth band adapted to pass frequencies from about 2286 Hz to about 2856 Hz; a sixth band adapted to pass frequencies from about 2857 Hz to about 3248 Hz; and a seventh band adapted to pass frequencies from about 3249 Hz to about 4000 Hz.
- a voicing cutoff frequency estimator adapted to receive respective frames of said speech signal and to determine a corresponding voicing cutoff frequency value for each of said respective frames, and to provide said voicing cutoff frequency value to an output port, said voicing cutoff frequency estimator comprising a bandpass filter means; and
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5. A method for generating a voicing cutoff frequency identifying a frequency below which periodic voicing predominates and above which noise components predominate, said method comprising the steps of:
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applying speech to be analyzed to a bank of filters including bandpass filters, to thereby generate signals in disparate bands; rendering unipolar the signals in each of the disparate bands, to produce unipolar signals; filtering said unipolar signals associated with each of said disparate bands, to thereby eliminate direct signal components in the resulting filtered unipolar signals associated with each of said disparate bands; autocorrelating each of said filtered unipolar signals associated with said disparate bands, to thereby determine the maximum value of the autocorrelated signal associated with each band; determining a voicing cutoff frequency by comparing each of said maximum values with a fixed threshold value, to thereby associate with each of said bands one of a true and false state; and selecting as a putative voicing cutoff frequency the upper frequency of that band which both (a) has a true state and (b) represents a frequency below which no two adjacent bands have a zero state. - View Dependent Claims (6, 7, 8, 9, 10, 11, 12, 13)
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Specification