An efficient algebraic codebook search for G.729 speech codec

In a bid to enhance the search performance, this paper presents an improved version of reduced candidate mechanism (RCM), an algebraic codebook search conducted on an algebraic code-excited linear-prediction (ACELP) speech coder. This improvement is made based on two findings in a piece of our prior work. The first finding is that there is a 0.8321 probability that the number 1 ranked pulse in a global sorting by pulse contribution is indeed one of the optimal pulses, and the second is that the speech quality can be well maintained at an accuracy rate above 50% approximately. Hence the number 1 pulse in the global sorting is labeled as one of optimal pulse, following which a sequence of search tasks are fulfilled through RCM. This proposed complexity reduction algorithm, implemented on a G.729A speech codec, takes as few as 8 searches, a search load tantamount to 2.5% of G.729A, 12.5% of global pulse replacement method (iteration=2), 16.7% of iteration-free pulse replacement method and 50% of RCM (N=2). This proposal is thus found to successfully reduce the required computational complexity to a great extent as intended.