Sound Level Meters

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Testing and validation are indispensable steps in the

development of software platforms designed to emulate

hardware components. Since modern sound level meters rely

heavily on digital signal processing for sound analysis, it seems

reasonable to expect that results of equal or greater accuracy

can be realized on computer platforms. Requirements for

precision measuring instruments are specified in the

international standard IEC 61672-2003 – Electroacoustics –

Sound Level Meters. The Standard is applicable to selfcontained

or multi-component analogue and digital hardware

systems, only briefly mentioning computer software as a

provisional part of the instrument for displaying results and

limited data manipulation.

On the other hand, modern digital multi-channel systems

provide means of storing recorded waveforms on a PC hard

disk, thus being fully dependent on dedicated software for all

subsequent processing and analysis. Once integrated with

hardware into a complete sound measuring instrument, such

computer software becomes a subject to compliance with

international standards calling for pattern evaluation tests and

periodic testing.

Measuring instrument comprises several components used for

acquisition, data manipulation, and analysis. Acoustical

transducer (typically a condenser microphone), signal

conditioner and analog-to-digital converter are used to first

convert the sampled analog signal into electrical voltage, and

then to its binary representation. Shelton [ ] recognizes this

part of the instrument as the real-time layer where the

instrument resources are dedicated to particular functions 100

% of the time.

Once the signal has been sampled in real-time, it is passed on

to the block-oriented la...

... middle of paper ...

...ere observed throughout most of the tests.

This was not the case for other common wave file sampling

rates (44.1 kHz, 51.2 kHz) as nominal frequencies of test

signal did not satisfy the condition of periodicity.

This issue is acknowledged in the audio metering realm and

documented in works by Lund and in IEC/TR 602680-18

Sound System Equipment - Peak Programme Level Meters -

Guide for Digital Audio Level Meter standard. However, the

topic was not dealt with in detail since level monitoring in

music and audio domains typically involves broadband signals

as audio input. Recommendations are given to exclude the

problematic “exceptional” test frequencies from global results.

This approach cannot be translated to pattern evaluation tests

for sound measuring instruments as these critical frequencies

provide the starting point for majority of electrical tests.

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