Measuring mis-match between signals

Abstract

The degree of mis-match which would be obtained between a test and a reference signal, for example speech signals, should their time-axes be subjected to that relative shift and/or distortion which is required to minimize the degree of mismatch is carried out by sampling the two signals at regular intervals and storing these samples in memories. All the samples of one signal are then read out in succession from one memory; each successive sample of the other signal is read out from the other memory, and the difference between each pair of samples is formed in a subtractor. Each difference value from the subtractor is added to the smallest of three quantities, X, Y and Z and the result stored in a register to form the new quantity X. This new quantity X is also stored in a further memory cyclically addressed in tandem with the memory 12. The quantity Z is the previous content of the location of memory into which the new quantity X is written, and the quantity Y is the previous value of the quantity Z, obtained by shifting the previous value of the quantity Z in a two-stage shift register. Thus the quantities X, Y and Z correspond to the present sample of the other signal and the immediately preceding sample of the one signal, the immediately preceding sample of both signals, and the present sample of the one signal and the immediately preceding sample of the other signal respectively. The result is that each successive value of the quantity X is the optimum cumulative distance value between the two signals for the corresponding pair of samples should these be assigned to each other when matching the two signals to each other. The process is continued until all the sampled value have been read and paired, at which point the value of the quantity X is a measure of the above-defined degree of mis-match.