Performance of an FFT-based voice coding system in quiet and noisy environments

This paper describes a 2400 bit/s vocoder based on spectral envelope estimation, spectral coding to 48 bits, pitch extraction, and decreasing-chirp excitation for voiced synthesis. Several spectral smoothing and coding schemes are described and intelligibility test results compared. This vocoder was implemented on the CSP-30 high speed digital processor at the RADC/EEV Speech Processing Research and Development Facility at Hanscom AFB, MA. This system yields high performance in a quiet environment and is robust in acoustic noise environments at a data rate of 2400 bits/s.