A Low Bandwidth Speech Coder Based on the Ratio Spectrum
We have implemented a low bandwidth speech coder using a new spectral representation called the ratio spectrum. The ratio spectrum is approximated in the digital domain by the normalized cumulative sum of the magnitude of the Fourier spectrum. This cumulative sum is guaranteed to be a monotonic nondecreasing function between zero and one. For each frame, frequency values are extracted by uniformly sampling along the ratio axis. These frequency values are coded and transmitted along with the overall power level, pitch and voicing information. The coder achieves a 1.59Kbps coding rate for intelligible speech. The speech quality of the coder can be improved by increasing the number of samples with subsequently higher bitrates. Introduction V/ UV Spectrum Analysis Formant Extraction