| Abstrakt: |
A new speech compressor is described. We have named this device the bandpass compressor (BPC) because it is based on the idea that the output of a narrow-band filter can be adequately described by means of two slowly varying parameters, the amplitude envelope, and the instantaneous frequency. In the BPC, amplitude information is conveyed as in a channel vocoder, but, instead of detecting and transmitting pitch and voicing information, a slowly varying instantaneous frequency is derived from each band-pass channel by means of a limiter, frequency discriminator, and low-pass filter. At the synthesizer, a frequency-tracking loop regenerates a square wave of the appropriate instantaneous frequency. This wave is modulated by the transmitted amplitude information and applied to a final bandpass filter. The compressed speech is the sum of the outputs from a bank of these bandpass filters. We estimate that a 16-channel BPC uses 800-cps bandwidth. If the BPC is used solely for recovering the base-band speech, which is then used to excite a voice-excited vocoder, we estimate that 525-cps bandwidth is needed. More testing must be done on the BPC (which has been simulated on a digital computer) before definitive statements can be made about its advantages and shortcomings. Preliminary results are quite encouraging. [ABSTRACT FROM AUTHOR] |
