Fast pitch tracking process for LTP-based speech coders

A process for deriving voice pitch related delay values M to tune a Long-Term Prediction (LTP) filter to be used in an LTP-based speech coder converting a speech derived digital signal r(n) into a lower bit rate signal, said filter being provided with a variable length delay line fed with a reconstructed signal r'(n), and said process including:

• a) splitting said r(n) signal into N samples long consecutive segments;
• b) splitting each segment into j sub-segments, j being a preselected integer;
• c) cross-correlating the first current signal sub-segment with a previously reconstructed signal segment to derive therefrom a cross-correlation function R(n), wherein:
• ##EQU5## for n=k' to N d) sorting the R(n) values for peak location R(M1), setting the filter delay to M1 and shifting the signals samples over one sub-segment;
• e) computing samples indexes n for a predefined number of samples located about M1 harmonics and sub-harmonics, i.e. located about M1/p, . . . , M1/3, M1/2, M1, 2M1, 3M1, . . . , pM1 wherein p is a predefined integer value and n=pM1+k where k is a predefined integer value;
• f) computing the cross-correlation function values R(n) for n defined in step (e);
• g) sorting the R(n) values for peak location to derive a new delay value M2;
• h) repeating steps (e) through (g) using M2 instead of M1, and so on up to Mj.