Fast significant sample detection for a pitch detector

DETAILED DESCRIPTION FIG.
1 shows an illustrative maxima locator which is the focus of this invention.
The maxima locator is responsive to frames of digital samples representing an analog speech signal received via path 11 for determining the significant samples.
Those frames of speech are preprocessed in the following manner.
In order to reduce aliasing, the speech is first low-pass filtered and then digitized and quantized.
The digitized speech is then divided, advantageously, into 20 millisecond frames with each frame comprising, illustratively, 160 samples.
Further, it would be obvious to one skilled in the art that the maxima locator could be responsive to other types of signals derived from the analog speech signal that can be utilized to determine the pitch.
One such signal is the forward prediction error or residual signal that results during the calculation of the LPC coefficients.
Consider now in detail the operation of maxima locator 10 of FIG.
1.
The latter locator is responsive to the samples of the speech frame illustrated in graphic form of FIG.
2 to produce the output signal on path 17 illustrated in FIG.
4.
Reverse search detector 12 is responsive to the samples illustrated in FIG.
2.
Only a subset of the 160 samples are illustrated.
Detector 12 starts with sample 159 and searches from right to left performing the following operations.
Detector 12 considers sample 159 a present candidate sample and stores the value of this sample.
Detector 12 then examines each sample to the left until it encounters another sample that has an amplitude greater than the present candidate sample or is the nineteenth sample from the present candidate sample being examined.
If the larger amplitude sample is encountered or the number of samples examined is equal to 19 samples from the present candidate sample, detector 12 stores that sample as a new present candidate sample and repeats the previous search procedure.
The basis for terminating the search after 19 samples and initiating a new search is the assumption that the highest pitch encountered in human speech is approximately 420 Hz which at a sample rate of advantageously 8 kHz results in 19 samples