COMPRESSION AND EXPANSION OF DIGITIZED VOICE SIGNALS

摘要

Apparatus and a method are disclosed for digitizing a voice signal as it occurs and the digitized signal is compressed and stored for subsequent reconversion to a voice signal at a later time. Binary words derived from digitizing the voice signal in an analog-to-digital converter represent the voice non linearly and are first linearized by a first processor and then stored in a first memory until a block of binary words are assembled. Next the block of binary words are transferred to a second buffer memory and a second processor compresses it using time domain harmonic scaling processing which extracts the pitch of the original voice and also compresses the voice frequency spectrum to affect a 2:1 reduction in the number of stored binary words representing the digitized voice signal. This reduced amount of data is then upsampled by a factor of four using linear interpolation to derive a pseudo higher sample rate required for further processing using continuously variable slope delta modulation processing which yields one binary bit out for every binary word processed. The resultant bits are assembled into eight bit words and then stored in a third memory. Another binary word representing the pitch is added and the result is a 4:1 compression of the original digitized data. The compressed digitized data is stored in a bulk memory. Thereafter, more digitized samples of the voice signal undergo this same processing. Compressed digitized voice signals may be reconverted to a voice signal for playback by processing the digitized and compressed voice signals generally in the reverse order. Playback speed control may also be accomplished without changing the pitch of the voice. To double the playback speed the time domain harmonic scaling processing is deleted in playback, thus leaving the frequency spectrum compressed and a 2:1 reduction in binary words representing the digitized voice. To slow the playback speed the digitized voice signals undergo modified TDHS processing.