Browse Prior Art Database

ADAPTIVE VOLUME CONTROL SYSTEM

IP.com Disclosure Number: IPCOM000007746D
Original Publication Date: 1996-May-01
Included in the Prior Art Database: 2002-Apr-18
Document File: 6 page(s) / 253K

Publishing Venue

Motorola

Related People

David Wiatrowski: AUTHOR

Abstract

In a mobile radio environment, comprising a mobile two-way radio device mounted in a service vehicle, there is a noted problem maintaining an appropriate output volume, above the vehicle's ambi- ent noise level, to the radio operator. The ambient noise present in the vehicle may include road noise, wind noise, engine noise, other radios' audible out- put (e.g., AM/FM broadcast, other band radio), and talking. For relatively long periods of time, the ambi- ent noise is not stationary, that is, its statistical char- acteristics are not constant over long periods oftime. The current method of maintaining an acceptable output volume level is strictly manual, and places the burden of monitoring and adjusting the output volume level entirely on the radio operator.

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MOTOROLA Technical Developments

ADAPTIVE VOLUME CONTROL SYSTEM

by David Wiatrowski

PROBLEM STATEMENT:

  In a mobile radio environment, comprising a mobile two-way radio device mounted in a service vehicle, there is a noted problem maintaining an appropriate output volume, above the vehicle's ambi- ent noise level, to the radio operator. The ambient noise present in the vehicle may include road noise, wind noise, engine noise, other radios' audible out- put (e.g., AM/FM broadcast, other band radio), and talking. For relatively long periods of time, the ambi- ent noise is not stationary, that is, its statistical char- acteristics are not constant over long periods oftime. The current method of maintaining an acceptable output volume level is strictly manual, and places the burden of monitoring and adjusting the output volume level entirely on the radio operator.

  To better illustrate this problem, consider a vehi- cle stopped in tralfic with the radio's volume adjusted to a comfortable listening level. As the vehicle accel- erates, engine noise and wind noise increase until the volume level is insufficient to compensate for the increase in ambient noise. The radio operator must make an appropriate adjustment in the radio's volume to ensure successful communication under this new ambient noise condition. Similarly, as the vehicle slows from a high rate of travel, the road noise and wind noise tend to decrease. If left uncompensated, the radio's volume level is set to an uncomfortably high level, requiring another adjust- ment. A series of high speed and low speed adjust- ments quickly becomes an annoyance to the radio operator; therefore, a method to automatically mon- itor and adjust the radio's volume level is needed.

SOLUTION:

  The solution to this nroblem is to simply change the radio's volume control to a signal to noise ratio control. Instead of specifying a desired volume level, the radio operator specifies an acceptable signal to noise ratio (SNR), implicitly set subject to the pres- ent ambient noise cot&ions. The radio monitors the SNR and makes appropriate adjustments to main- tain the desired signal noise ratio. Recall the signal to noise ratio is a ratio of the desired signal level to the noise level present in a system and is often expressed in decibels (dR). Mathematically,

Sh'R& = 2OlOg( 2;';:;)

  Computing the SNR, in the described environ- ment, is not necessarily a trivial task. There are sev- eral problems that must be overcome.

1) The ambient noise may not be measured directly, as it contains some unknown component of the desired signal, s(n).
2) The desired signal level, while known internally as s(n), manifests in a:slightly altered form within the acoustic enclosure. This is due to variability in the gain of the audio amplifier, speaker, and natural filtering of the signal within the acoustic enclosure.

  A digital adaptive filter may be capable of over- coming both of these problems. Adaptive filters are well known i...