the paper introduces the " algorithm of smv from the view of encoding and decoding, studies on the technologies such as signal modification scheme, gain determination scheme, the scheme of quantization and fixedcodebook structure that smv employed to improve the synthesized speech quality . the paper also contrasts it to other existed speech coding standard on the frame length, rate, mos and complexity 本文詳細介紹了可選模式聲碼器的編碼和解碼算法,重點研究了其用于提高合成語音質量的關鍵技術,包括信號修正機制、增益判定機制、固定碼本結構以及量化機制,并將smv與其它語音編碼算法就幀長、速率、mos得分和復雜度四個方面進行比較。