Browse Prior Art Database

Fundamental Frequency Detector

IP.com Disclosure Number: IPCOM000092186D
Original Publication Date: 1968-Oct-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 41K

Publishing Venue

IBM

Related People

Hurel, DG: AUTHOR [+2]

Abstract

The system is composed of bandpass filter 1, peak detector 2, variable time constant single-shot 3, and low-pass filter 4. Single-shot 3 has transistors T1, T2, and operational amplifier A. Diodes D1, D2, resistors R1...R7, and capacitor C are used in the circuit. The information contained in capacitor C is compared with a variable level. This last is controlled by the output signal of filter 4 which is applied to amplifier A through R7.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 69% of the total text.

Page 1 of 2

Fundamental Frequency Detector

The system is composed of bandpass filter 1, peak detector 2, variable time constant single-shot 3, and low-pass filter 4. Single-shot 3 has transistors T1, T2, and operational amplifier A. Diodes D1, D2, resistors R1...R7, and capacitor C are used in the circuit. The information contained in capacitor C is compared with a variable level. This last is controlled by the output signal of filter 4 which is applied to amplifier A through R7.

When a complex signal, such as voice, is applied at the input of the system, filter 1, operating in the frequency band 70-300 Hertz, produces a signal as shown in the drawing. The time interval between two consecutive maxima such as M1 and M2 is related to the fundamental frequency of the signal. By using detector 2, single-shot 3 and filter 4, the output of filter 4 is a voltage varying as a function of the fundamental frequency.

Some interferences I occur in the filter 1 output signal which are detected as maxima by detector 2 and are applied on the single-shot 3 input with the other maxima. If the time constant of single-shot 3 has a value t, all the interference maxima happening in a time lower than t are suppressed by single-shot 3. Those happening in a time higher than t control single-shot 3 and then provide erroneous information at the output of filter 4. The function of the latter is to integrate the output pulses of single-shot 3 to obtain a voltage which varies in relation to fundamental...