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Voice Detector Circuit

IP.com Disclosure Number: IPCOM000088992D
Original Publication Date: 1977-Sep-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Frankeny, RF: AUTHOR

Abstract

A circuit for the detection of initial voiced word sounds converts the number of audio zero crossings in a fixed time interval to a voltage level and compares the difference in voltage in any two consecutive time intervals to a predetermined voltage interval determined by resistor R3, variable resistor R4, and resistor R5. If the difference voltage is outside the interval, then an output signal is generated which can be used to start a recorder or other audio processing devices.

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Voice Detector Circuit

A circuit for the detection of initial voiced word sounds converts the number of audio zero crossings in a fixed time interval to a voltage level and compares the difference in voltage in any two consecutive time intervals to a predetermined voltage interval determined by resistor R3, variable resistor R4, and resistor R5. If the difference voltage is outside the interval, then an output signal is generated which can be used to start a recorder or other audio processing devices.

Referring to the figure, an audio input signal is shaped by comparator 1 around zero volts, with resistors R1 and R2 providing hysteresis. Single shots 2 and 3 generate positive pulses 100 microseconds wide on the leading and trailing edges of the shaped audio signal, respectively. Gate 4 OR's these pulses. These zero crossing pulses are gated by the clock 24 through NAND gates 5 and 6 to transistors 7 and 8 on positive and negative clock pulses, respectively.

When the clock 24 is positive, negative pulses from NAND gate 5 turn transistor 7 off, allowing constant current source 9 to charge capacitor C1 through diode 10 with pulses of current. These pulses charge capacitor C1 to a voltage proportional to the number of pulses (zero crossings of audio) occurring during the positive clock. When the clock goes negative, the charge on capacitor C1 is held by diode 10 and presented to the differential amplifier 11. During the negative clock period, the complementary functi...