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Automatic Audio Amplifier Volume Control Device

IP.com Disclosure Number: IPCOM000108017D
Original Publication Date: 1992-Apr-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 4 page(s) / 155K

Publishing Venue

IBM

Related People

Powell, KE: AUTHOR [+2]

Abstract

Described is a circuit implementation of an audio amplifier volume control device. The device is designed to automatically control the output volume of an audio amplifier sound system relative to ambient noise.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 48% of the total text.

Automatic Audio Amplifier Volume Control Device

       Described is a circuit implementation of an audio
amplifier volume control device.  The device is designed to
automatically control the output volume of an audio amplifier sound
system relative to ambient noise.

      The concept described herein provides a means of automatically
maintaining the volume of an amplifier at a perceptible margin above
variable ambient noise levels.  The device eliminates the need to
manually control the sound system's output volume level when
variations in the ambient noise environment occur, as well as
amplitude variations in program material applied to the sound system.

      Fig. 1 shows a block-diagram overview of the audio amplifier
volume control device.  The audio input signal from an audio
amplifier (not shown) is applied to automatic gain control (AGC)
amplifier 10.  The output of AGC amplifier 10 is applied to power
amplifier 11 which is capable of driving high quality speaker units
(not shown). A sensor (not shown) senses the ambient noise so that
its output can be applied to pre-amplifier 12 which is a low level
audio pre-amplifier. The output of pre-amplifier 12 is applied to LOG
amplifier 13 which is a logrithmic amplifier.  A sampling of the
audio signal from AGC amplifier 10 is applied to LOG amplifier 14.

      The outputs of LOG amplifiers 13 and 14 are applied to
controller 15.  LOG amplifiers 13 and 14 are a plurality of
integrated circuits (ICs) consisting of a differential amplifier, a
resistor/capacitor filter, buffers and a summing amplifier.
Controller 15 is used to develop a control signal relative to the
ambient noise level.  The output from controller 15 is fed back to
the gain control input of AGC amplifier 10 so as to maintain a
desired level above the ambient noise.  This level is maintained
without having speakers provide a modulating force for an ambient
sensor.

      Fig. 2 shows a block diagram of a single channel of the audio
signal path through the audio amplifier control device signal
section, as shown in Fig. 1.  When the audio input signal is applied
to AGC amplifier 10, its output is applied to power amplifier 11 and
to LOG amplifier 14 through resistors R1 and R2.  The values of
resistors R1 and R2 are such that a specific current is applied to
LOG amplifier 14 when the audio input signal is at its maximum.  LOG
amplifier 14 is designed to provide a conversion of the audio input
signal to a DC voltage level.  This conversion is necessary since the
signals change exponentially in relation to the perception of the
sound pressure levels. The output of LOG amplifier 14, in conjunction
with resistor R3, maintains a constant voltage level.

      Fig. 3 shows a block diagram of the ambient signal section of
the audio amplifier control device.  The ambient audio signal, as
applied to pre-amplifier 12, originates from a small microphone
element (not shown) that is placed to monitor t...