TABLE OF CONTENTS The idea behind analysis-by-synthesis at the encoder is to analyse a frame (or more) of speech, and extract parameters from this. These parameters are then used to create a frame of reconstructed speech. The frames of original and reconstructed speech are then compared to see how closely they match. Some part of the parameter extraction process is then varied to create a slightly different set of parameters, which are in turn compared to the original speech.
Perhaps several hundred iterations are made across a search space, and the best set of parameters (based on how close the match is between original and reconstructed speech) are then transmitted to the receiver. Something to consider is that the parameters may need to be quantised before being transmitted to the decoder. In this case the quantised-dequantised parameters are the ones used by the encoder to check how good is the matching.
Before we look at the most famous of the analysis-by-synthesis coding structures, it is important to remember that degree of matching , calculated as a difference between vectors, may not relate at all to how a human perceives degree of difference. As a very trivial example, imagine a continuous sinewave original signal. Next imagine a version which is delayed by a few degrees. The degree of matching in a mean-squared sense will be quite low in fact it may be less than the matching between the original sinewave and random noise. However the perceived difference between the sinewaves is...
