Multi-pulse speech coder
First Claim
Patent Images
1. A method of speech coding comprising:
- receiving speech samples;
processing the speech samples to derive parameters representing a response of a synthesis filter;
deriving, from the parameters and the speech samples, pulse position and amplitude information defining an excitation consisting, within each of successive time frames corresponding to a plurality n of said speech samples, of a pulse sequence containing a smaller plurality k of pulses;
wherein the pulse position and amplitude information of the k pulses is derived by;
(1) deriving an initial estimate of the positions and amplitudes of the k pulses, and(2) carrying out an iterative adjustment process by;
(a) selecting individual ones of the k pulses according to predetermined criteria, and(b) substituting for each such selected pulse a pulse in an alternative position whenever a computed error signal is thereby reduced, said error signal being obtained by comparing speech samples with the response of a filter having said parameters to an excitation which includes said selected pulse and others of said pulses, said substituted alternative position thereby being obtained as a function of the position and amplitudes of said other pulses.
1 Assignment
0 Petitions
Accused Products
Abstract
Speech is coded such that it can be generated by a pulse excitation sequence filtered by an LPC (linear preductive coding) filter. The sequence contains, in each of successive frame periods, pulses whose positions and amplitudes may be varied. These variables are selected at the coding end to reduce the error between the input and regenerated speech signals. The selection process involves derivation of an initial estimate followed by an iterative adjustment process in which pulses having a low energy contribution are tested in alternative positions and transferred to them if a reduced error results.
-
Citations
18 Claims
-
1. A method of speech coding comprising:
-
receiving speech samples; processing the speech samples to derive parameters representing a response of a synthesis filter; deriving, from the parameters and the speech samples, pulse position and amplitude information defining an excitation consisting, within each of successive time frames corresponding to a plurality n of said speech samples, of a pulse sequence containing a smaller plurality k of pulses; wherein the pulse position and amplitude information of the k pulses is derived by; (1) deriving an initial estimate of the positions and amplitudes of the k pulses, and (2) carrying out an iterative adjustment process by; (a) selecting individual ones of the k pulses according to predetermined criteria, and (b) substituting for each such selected pulse a pulse in an alternative position whenever a computed error signal is thereby reduced, said error signal being obtained by comparing speech samples with the response of a filter having said parameters to an excitation which includes said selected pulse and others of said pulses, said substituted alternative position thereby being obtained as a function of the position and amplitudes of said other pulses. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 12)
-
-
11. A method according to claim 11 in which the energy gain function for each pulse is obtained from a lookup table having entries for energy intervals and corresponding energy gain functions, the lookup table having been empirically derived from a training sequence of speech.
-
13. An apparatus for speech coding comprising:
- means for receiving speech samples;
means for processing the speech samples to derive parameters representing a response of a synthesis filter; means for deriving, from the parameters and the speech samples, pulse position and amplitude information defining an excitation consisting, within each of successive time frames corresponding to a plurality n of said speech samples, of a pulse sequence containing a smaller plurality k of pulses; wherein the means for deriving pulse position and amplitude information of the k pulses includes; (1) further means for deriving an initial estimate of the positions and amplitudes of the k pulses, and (2) means for carrying out an iterative adjustment process by; (a) selecting individual ones of the k pulses according to predetermined criteria, and (b) substituting for each such selected pulse a pulse in an alternative position whenever a computed error signal is thereby reduced, said error signal being obtained by means for comparing speech samples with the response of a filter having said parameters to an excitation which includes said selected pulse and others of said pulses, said substituted alternative position thereby being obtained as a function of the position and amplitudes of said other pulses. - View Dependent Claims (14, 15, 16, 17, 18)
- means for receiving speech samples;
Specification