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Digital Pitch Detector using Delta Modulator and Limited Length Bit Pattern Generator

IP.com Disclosure Number: IPCOM000079770D
Original Publication Date: 1973-Sep-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 3 page(s) / 42K

Publishing Venue

IBM

Related People

Frei, AH: AUTHOR [+3]

Abstract

This is a pitch detector for speech recognition purposes, in which the pitch period is determined by the extraction of certain binary information from delayed and undelayed streams of delta-modulated bits.

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Digital Pitch Detector using Delta Modulator and Limited Length Bit Pattern Generator

This is a pitch detector for speech recognition purposes, in which the pitch period is determined by the extraction of certain binary information from delayed and undelayed streams of delta-modulated bits.

Referring to Fig. 1, the adaptive delta modulator that receives the sampled audio input signal includes, in its feedback loop, a multiplier 1 whose multiplication factor is controlled by a stepsize controller 2, which furnishes an output related to the steepness or flatness of the input signal. Hence, the normal decoded feedback signal furnished by the accumulator or digital-to-analog converter 3 is now selectively multiplied, before being applied subtractively to the differential amplifier 4. What the threshold comparator or quantizer 5 sees, therefore, is not the true difference between the input signal and the decoded delta-modulated signal, but a deliberately distorted differential relationship that results in a delta-modulated signal which actually embodies more useful information for analytical purposes.

The quantized delta bits (delta) are fed concurrently to shift registers S1 and S2, one of which introduces a delay interval tau in the hit stream. The sign of the audio input signal also is detected by the comparator or quantizer 6, and the sign bits are fed concurrently to shift registers S3 and S4, one of which introduces a delay tau. The shift registers have a length sufficient to afford a suitable "window" larger than the pitch period to be detected.

The four output signals from the shift registers are applied to a binary feature extractor 7, which examines the delta bit sequences to extract first-order and second-order derivatives. Each first-order derivative, based upon the relationship between two neighboring bits, denotes by its +1, 0 or -1 value, whethe...