A Walsh Vocoder

Abstract

<p>The concepts of the analogue channel vocoder and digital FFT vocoder are utilized in the analysis of a Walsh vocoder. The FFT and Walsh vocoders are simulated in Fortran on a CDC6400 computer. The simulations contain a simplified cepstrum pitch detector to simulate a hardware pitch detector. The Walsh vocoder simulation is identical to the FFT vocoder simulation with the Fast Walsh Transform operation replacing the Fast Fourier Transform operations (FWT and FFT respectively) in the channel signal calculations and transforms into the time domain.</p> <p>Sentences of different lengths and speakers are processed by the simulated vocoders and the resultant synthesized speech is analyzed for comparative quality and intelligibility.</p> <p>An unsuccessful attempt is made to effect a vocoder which does not require a pitch detector with the calculation of the time invariant sequency power spectrum replacing the channel signal calculations in the vocoder simulations. Long term frequency and sequency enveloped are used to shape the frequency and sequency power spectra derived from the transmitted time invariant sequency power spectrum in the FFT and Walsh vocoder simulations respectively.</p>