Browse Prior Art Database

VOICE ADAPTED MICROPHONE

IP.com Disclosure Number: IPCOM000007491D
Original Publication Date: 1995-Jul-01
Included in the Prior Art Database: 2002-Apr-01
Document File: 4 page(s) / 120K

Publishing Venue

Motorola

Related People

S. Lichtetfeld: AUTHOR [+3]

Abstract

Communications systems typically have a lim- ited bandwidth in which to transmit voice informa- tion. The audio frequency range of such voice infor- mation is generally limited to bandwidths of300 Hz to 3 kHz. Acoustic couplers, e.g. loud speakers and microphones, are used to enunciate the voice from audio signals output to the speaker or to generate audio signals from a voice input to a microphone.

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 50% of the total text.

Page 1 of 4

MOTOROLA Technical Developments

VOICE ADAPTED MICROPHONE

by S. Lichtetfeld, D. Auth and W. Zuber

  Communications systems typically have a lim- ited bandwidth in which to transmit voice informa- tion. The audio frequency range of such voice infor- mation is generally limited to bandwidths of300 Hz to 3 kHz. Acoustic couplers, e.g. loud speakers and microphones, are used to enunciate the voice from audio signals output to the speaker or to generate audio signals from a voice input to a microphone.

  The performance of such acoustic couplers has a major influence on the perceived audio quality of the voice or on the generation of the audio signals. This influence is primarily due to the couplers hav- ing a non-flat gain response across the audio fre- quency range, e.g. a microphone would typically amplify audio signals to higher amplitude levels at frequencies above 2 kHz. Figure 1 shows that the audio frequency response associated with male (Figure la) and female (Figure lb) voices is also var- iable across the audio frequency range. The com- bined effect of the variable frequency response of both the acoustic coupler combined with the human voice pattern may result in perceived audio distor- tion ofthe voice.

  Hence, it would be very beneficial, if audio cir- cuitry automatically adapted to, and compensated for, this combined frequency response of acoustic couplers and human voice patterns.

of typical human speakers as well as for acoustic couplers, the modulated audio input signal can be divided and processed as shown in Figure 2a. The usable frequency range is divided into three bands each ofwhich can be independently automatic-level controlled by three voltage controlled filters. The voltage controlled filters are used independently to control the level ofthe audio signal across the trans- mitted audio bandwidth. Figure 2b shows that this results in a much more constant audio frequency response of a processed male voice.

  Figure 3 shows circuitry for a two band-split adap- tive microphone amplifier. The circuit includes a first bandpass fil...