Short Time DFTコンパンダの提案とその構成

Abstract

The syllabic compander reduces fading noise to improve speech quality over poor radio channels. However, conventional syllabic companders are suffered from such distortions as harmonics and intermodulations owing to employing AM demodulator to estimate signal envelope. Short time DFT syllabic compander is newly proposed here with emphasis on employing concept of instantaneous spectrum to detect envelopes instead of approximation of AM demodulation in realizing the envelope detectors. The instantaneous spectrum analysis, which separates time resolution from frequency resolution, puts the short time DFT compander on the stage of developing exact companders for the radio communication systems. The short time DFT compander is discussed in this paper with emphasis on how to operate on the frequency domain and how to get efficient processing against tremendously great amount during analyzing instantaneous spectrum. Multi-rate sampling is also successfully employed to speed up analysis in the short time DFT compander without almost any degradation.