Abstract: A transmission system for encoded transmission of audio signals with frequency band compression. An input signal to be transmitted is divided into two spectral portions in a coder. One spectral portion is digitally encoded by a time-domain coder, and the other spectral portion is coded by a transform domain coder. The two digitally coded signals are then multiplexed for transmission as a composite digitally coded signal to a receiver. At the receiver the composite signal is demultiplexed and the two spectral portions thereof are respectively decoded by a time-domain decoder and a transformer-domain decoder. The decoded signals, covering the respective spectral portions, are then combined to reconstitute the originally transmitted audio signal.

Abstract: An audio signal digital transmission system wherein the signal is sampled and successive segments each of N samples are digitally encoded. Encoding has heretofore been effected by vector quantization, whereby a memory stores a book of a large number of codewords corresponding to possible segments of successive signal samples, and the best matching stored segment is determined by calculation. The present invention bases encoding on comparison of the envelope of a signal segment with a limited number of reference envelopes. The best matching reference envelope is selected, and an identifying codeword therefore is transmitted along with related parameters. A receiver reproduces the signal from the reference envelope and the related parameters. Since identified envelopes of the signal segments are less variable and simpler to evaluate than the signal samples in the segments, a considerable reduction of memory capacity and calculation complexity is achieved.