Sound Level Meters

1167 Words5 Pages
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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