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Browse Prior Art Database

Multimedia Headphone Automatic Volume Normalization

IP.com Disclosure Number: IPCOM000105037D
Original Publication Date: 1993-Jun-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 4 page(s) / 135K

Publishing Venue

IBM

Related People

Beers, GE: AUTHOR [+2]

Abstract

Disclosed is a circuit and algorithm to allow automatic volume control for the various impedances presented by different headphones when plugged into computer multimedia audio cards. The method allows normal- ization of sound over various sets of headphones. Briefly, this circuit is operated by driving a single channel output to a known level and measuring the resultant level with the Analog-to-Digital convertor after it has passed through a network (refer to Fig. 1 for detail). Software in addition to hardware is required for this circuit to be implemented.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 44% of the total text.

Multimedia Headphone Automatic Volume Normalization

      Disclosed is a circuit and algorithm to allow automatic volume
control for the various impedances presented by different headphones
when plugged into computer multimedia audio cards.  The method allows
normal- ization of sound over various sets of headphones.  Briefly,
this circuit is operated by driving a single channel output to a
known level and measuring the resultant level with the
Analog-to-Digital convertor after it has passed through a network
(refer to Fig. 1 for detail).  Software in addition to hardware is
required for this circuit to be implemented.

      Multimedia equipment often requires headphones for listening.
This keeps the noise level, for a room filled with multimedia
machines, down so that someone working at one machine producing audio
does not inter- fere with someone working at an adjacent machine.
Headphones are also used to provide cheap high quality sound for
multimedia presentations.  Headphones may tend to move around from
machine to machine in a class- room or any environment containing
several multimedia machines.

      The problem with using headphones is that different headphones
may present different loads to the audio circuits which are driving
the headphones.  Because the headphone load on the input circuitry is
different, the volume (or voltage) level heard through different
head- phones will be different.  A set of headphones which present a
small impedance to the drive circuit will have a much louder volume
than a set of headphones which present a large impedance.  The
sensitivity of the headphones also contributes to determine the
loudness for a given input level.

      A detailed description of the circuit and algorithm operation
is described next.  Given a personal computer multimedia audio card
with the following functions:  an Analog-to-Digital Converter (ADC)
input, a processor to examine and manipulate input data and an output
connector for stereo headphones the circuit can be examined closer.
The circuit shown in Fig. 1 allows for plugging of a set of
headphones into the circuit.  The headphones present an impedance to
the circuit; RH-L for the left stereo channel and RH-R for the right
stereo channel.

      To determine the headphone impedance presented to the circuit
by the left channel (shown as RH-L):  the drive amplifiers for both
the left and right channels are to be independently driven.  The left
channel will be driven with a known analog voltage (either AC or DC,
but not 0 or ground level).  The left channel drive voltage is shown
as VL and should preferably be driven at the extreme possible range
(full swing for AC or maximum offset for DC).  The right channel,
shown as VR, should be driven at the zero or ground level.

      By sampling the voltage level at V3 (junction between resistors
R3 and R4) using the Analog-to-Digital Converter (ADC), it is
possible to detect a change in the max...