Speex Speech Codec Algorithm And Its Implementation On DSP

With the development of the IP technology, VoIP (Voice over IP) receives more and more person's favors in recent years. And the rapid development of DSP makes the real-time implementation of complicated speech compression algorithm possible. Fixed-point DSP chips are popularly used in the multimedia field, such as processing of audio and video, for their good cost performance. This paper mainly researches how to use the fixed-point DSP chip ADSP2181 of ADI Company to realize speech codec algorithm over VoIP phone.At present, there are many standards and algorithms what have been implemented on this chip series, such as G.711, G.721, G.729.A, G.723 and ILBC. However, because of the background of proposal of the algorithms and the characters of the algorithms themselves, most of the algorithms have the patent limit or sole transmission rate in the VoIP application. Thus Speex, which does not have the patent limit, completely free, and may provide many kinds of transmission rates, is needed.Speex is an algorithm that integrates the narrow band, the wide band and the ultra-wide band together. It also supports the dynamic bit rate cut and in order to obtain better voice quality, it can also choose the different speech coding speed auto-adapted according to the network and the terminal actual situation to reduce the error and the influence from packet losing.The paper is about the research on algorithm and the implementation on 24bit fixed-point DSP chip. The paper also includes some discussion about the code optimization to reduce the algorithm complexity and raised the coding efficiency. So the research mainly includes the following several parts:First, translate the existing fixed-point C code to DSP assembly code. During this process let the program pass lots of test sequences to guarantee procedure accuracy. Second, aiming at the ADSP2181 processor's characters do some optimization to Speex algorithm. After optimization, Speex encoding algorithm's operating speed has been enhanced about 40%.Speex speech codec has been used in an actual VoIP phone terminal.