Bruel & Kjaer 4427 Noise Level Analyzer

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The Bruel & Kjaer 4427 Noise Level Analyzer is a portable instrument especially well suited for environmental noise measurements. The input stage and a digital detector/ averager have been carefully designed to give the Bruel & Kjaer 4427 a wide dynamic range of 110 dB. This noise level analyzer has been rated as Type 0 accuracy, according to IEC 651 and ANSI S 1.4 standards for sound level meters and IEC Publication 804 for integrating / averaging sound level meters.

This has been achieved by feeding the A or Lin. (20Hz-20kHz) frequency weighted signal to a precision logarithmic rectifier covering a very wide dynamic range, and sampling the output of the rectifier at a frequency of 131072 Hz. Detection and averaging is thereby a purely digital process, overcoming the practical limitations often met in analog averagers. The high input sampling frequency ensures that even very short impulses are correctly integrated. The Bruel & Kjaer 4427 has two distinct outputs, an SPL output and an energy average output.