Low data rate speech encoder with mixed excitation

A signal transmission system, for receiving information signals at an input port, and for transmitting the information signals over a limited-bandwidth path to a reproducing arrangement, said system comprising:

• pitch tracking means coupled to said input port, for determining the average pitch value of said information signals during each of a plurality of recurrent, sequential frame intervals, to thereby generate average pitch value signals;
• frame portion power determining means coupled to said input port, for dividing each of said frames into at least first and second temporal portions, and for determining the power in said information signals during at least said first temporal portion of each of said frames, to produce frame power signals;
• autoregression coefficient analyzing means coupled to said input port, for, during each of said frame intervals, generating at least ten autoregression coefficients from said information signals, representing line spectrum frequencies;
• pitch epoch detecting means coupled to said input port and to said autoregression coefficient analyzing means, for, during each frame, determining at least amplitude and time interval pitch parameters of said information signals, to thereby produce pitch parameter signals;
• periodicity analysis means coupled to said pitch epoch detecting means, for analyzing said pitch parameter signals, to form periodicity parameter signals in response to the presence or absence of voiced components in said speech and the periodicity of pitch pulses if said pitch pulses are periodic, and the ratio of the largest to the smallest pitch intervals if said pitch pulses are aperiodic, to produce jitter-representative signals;
• a filter bank coupled to said input port, said filter bank including a plurality of filters, each covering a different portion of the expected bandwidth of said information signals, for filtering said information signals into a plurality of nonoverlapping frequency bands, to thereby form a plurality of bandlimited signals;
• correlation means coupled to said filter bank and to said pitch tracking means, for correlating said band-limited signals at an interval responsive to said average pitch value signals, to thereby form estimated mixture signals;
• jitter correction means coupled to said correlation means and to said periodicity analysis means, for correcting said estimated mixture signals in response to said periodicity parameter signals, to thereby generate corrected correlation signals;
• coding means coupled to said pitch tracking means, to said frame portion power determining means, to said correlation means, and to said autoregression coefficient analyzing means, for generating codewords representative of said average pitch value signals, said frame power signals, estimated mixture signals, and said line spectrum frequencies, respectively, for producing codes;
• codeword generating means coupled to said coding means and to said periodicity analysis means, for joining said codes with said jitter-representative signals to form codewords for transmission;
• transmitting means coupled to said codeword generated means, for transmitting said codewords over said path;
• and
• reproducing means, coupled to a receiving end of said path, for receiving said codewords, and for decoding said codewords, and for generating a simile of said information signals.