LOW DELAY PITCH DETECTIOX USIKG DYNAMIC-PROGRAMMINGKITERBI TECHNIQUES*
P.M.B. Gambino, Lee Burnett · 1996
An algorithm for the detection of the Fundamental Pitch Period (F,) at low delay, utilising Dynamic Programming (DP) Techniques and those of the Viterbi Algorithm (VA) is presented [I], [2], [3]. The algorithm results in a low delay, accurate pitch detector which is vital for low rate speech coders, such as those utilising Prototype Waveform Interpolation (PWI) techniques [4]. Current methods, based on autocorrelation incur a significant look-ahead delay and are therefore considered unsuitable for use in such speech coders [5]. mapping for the signal segment under test, cs(i), to that of a similar signal segment ss(j) (refer to Figure 1). The objective is to determine an optimal relationship between the two signal segments based on the minimisation of an accumulated residual error. This is achieved by the use of the Partial Error Criteria, D(ij) which is defined as the minimum accumulated sum of residual errors from an unknown point i = 0, (j = unknown), to the point (ij) in the time warped plane. A PEC vector which traverses the D(ij) plane, replaces the linear distance summation which is equivalent to a linear trajectory in such a plane. The calculation of D(ij) is performed non-linearly over the required interval, as shown in equation (1) below: The algorithm described uses improved, non-linear Pitch Detection [6], with a substantial extension of a Viterbitype tracking algorithm to maintain a smooth pitch track.