Bandwidth compression by means of vocoders

Speech information may be transmitted over a bandwidth one tenth of that required for the original speech if attention is directed toward reproducing the envelope of the power density spectrum rather than the waveform itself. Pitch information can be transmitted independently of the spectrum information and the two sets of signals combined at the receiving end to resynthesize the original speech sounds. In the vocoder the power spectrum is analyzed and synthesized by means of band-pass filters. The energy for the voiced sounds is obtained from an oscillator called a buzz source, and for the fricative consonants the energy is obtained from a white noise source.