Very Low Bit Speech Coding Using Fractal Systems.

本文介绍了一种新提出的1.2kbpsis极低比特率语音编码器。该编码器类似于LPC声码器，利用频率为基频倍数的正弦信号合成语音信号，并根据听觉特性自适应地调制幅度，以提高语音质量。本文介绍了这种新型正弦信号合成器的基本原理，并说明了如何根据感知特性对正弦信号进行调制。听觉感知特性用GammatonFilters进行了模拟。提出了一种新的基于DP匹配的光谱信息(LSP系数)分段编码器，将总码率降低到1.2kbps。通过5个等级的MOS测试，合成语音的主观均衡度比简单LPC声码器提高了1.0。

A very low bit rate speechcoder at 1.2kbpsis newly proposedln this coder which is similar to the LPC vocoder, speechsignal is synthesizedusing sinusoids whose frequenciesare multiple of the fundamental frequency, and whose amplitudes are adaptively modulated based on auditory perceptualcharacteristics, in order to improve the quality.In this study, the basics of the new sinusoids synthesizerare introduced, thenhow to modulate the sinusoids based on perceptual characteristics is explained. The auditory perceptual characteristics are simulated by Gammatonefilters. And a new segment coder of spectral information (LSP coefficients) using DP matchingis also proposedtoreduce the total bit rate to 1.2kbps. According to MOS test (5 grades), the subjectivequality of the synthesized speech is improved by 1.0 compared with that of the simple LPC vocoder.