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Digital Impulse Sound Level Meter

IP.com Disclosure Number: IPCOM000081359D
Original Publication Date: 1974-May-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 20K

Publishing Venue

IBM

Related People

Maling, GC: AUTHOR [+2]

Abstract

A digital detector is proposed which can be used with a standard sound-level meter. The main feature of this detector is that it operates by digitizing the time signal directly, and computing a value which is not only in good agreement with the value obtained by a standard rms analog detector when the noise is steady, but leads to a higher reading when the noise fluctuates or is impulsive in character.

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Digital Impulse Sound Level Meter

A digital detector is proposed which can be used with a standard sound-level meter. The main feature of this detector is that it operates by digitizing the time signal directly, and computing a value which is not only in good agreement with the value obtained by a standard rms analog detector when the noise is steady, but leads to a higher reading when the noise fluctuates or is impulsive in character.

The detection method takes advantage of the fact that the short-time fluctuations in the spectrum of impulsive noise are known to be considerably greater than the short-time spectral fluctuations in steady noise.

In a standard digital rms detector, only the sum of the squares of the detector output are accumulated. At the end of a given integration period this sum-of- squares may be converted into the rms voltage, or into a decibel reading related to the rms voltage. In the present arrangement, the detector contains a second square/sum box which accumulates the sum of the fourth power of the filter outputs. At the end of an integration period, the sum of the squared values and the sum of the fourth power are combined to produce a sound pressure level.

The algorithm for the output device is to take a fraction of the mean-square accumulated level plus a fraction of the square root of the accumulated fourth power of the signal. Thus, the output is

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The Noise Pollution Level (NPL) is closely related to the output of this...