System for coding voice signals to optimize bandwidth occupation in high speed packet switching networks

A system for optimizing bandwidth in a High Speed Packet Switching Network, said system including a multirate voice coder including a first low bit rate coder section providing first coded sub-frames and a second coder section providing second coded sub-frames, said multirate coder including:

• said first coder section including:
• means for sampling the original voice signal and PCM encoding said sampled signal to derive therefrom PCM encoded samples S(n);
• means for feeding said S(n) data into short term filtering means (31) tuned by coefficients derived through so-called partial auto-correlation operations performed (30) over said S(n) to provide a short term residual signal r(n);
• a Long Term Prediction (LTP) loop (32, 33, 37) tuned by long term delay prediction coefficients derived from r(n) (34) and providing a signal e"(n) representing a Long term Prediction residual signal derived from a synthesized short term residual r'(n) and subtractor (35) for subtracting said e"(n) from r(n) to generate a Long Term error residual signal e(n), and first Block Coder means (39) for coding fixed length blocks of e(n) samples into sub-sampled blocks;
• and, multiplexor for multiplexing said coded fixed length blocks of e(n) wherein said partial auto-correlation, derived coefficients and said long term delay prediction coefficients are placed into said first sub-frame;
• said second coder section including:
• an adder for generating (r(n)-r'(n)) (36) and for feeding said (r(n)-r'(n)) into a second Block Coder 38 to generate said second sub-frame;
• and
• means for concatenating each said second sub-frames to the first sub-frame to generate said multirate coded frame at the highest predefined rate;
• wherein switching the multirate voice coder output rate from said highest predefined rate to said lowest rate needs only dropping said concatenated second sub-frame from said multirate frame.