SOUND ANALYSER
Electroacoustics / Acoustics

A machine comprised of a FILTER system and a system for indicating the relative energy passed through each part of the filter. This measurement gives the distribution of energy of the applied signal as a function of frequency called the SPECTRUM of the signal.

See: SONOGRAPHY, SPECTROGRAPH. Compare: FOURIER ANALYSIS, HELMHOLTZ RESONATOR, LEVEL RECORDER, OSCILLOSCOPE, SOUND LEVEL METER.

There are many types of analysers. An Octave Band Analyser measures the intensity level for each of a set of octave bands, centred on 31.5, 63, 125, 250, 500, 1000, 2000, 4000, 8000 and 16,000 Hz. A Third-Octave Band Analyser divides the frequency spectrum into three bands per octave, the Tenth-Octave Band Analyser into ten bands per octave.

See BROAD BAND NOISE, INFRASONIC, SPECTRUM, WHITE NOISE for examples of third-octave analyses. See: CENTRE FREQUENCY. Compare: CRITICAL BAND, Appendix E.

Other types of analysers include the Wave Analyser, which is a continuously variable analyser over the entire audio range; the Impact Noise Analyser for analysing IMPACT SOUNDs such as hammers or punch presses; and the Vibration Analyser, for analysing INFRASONIC VIBRATION.

STANDARD OCTAVE BAND FREQUENCIES

Centre Frequency (Hz)
Effective Band (Hz)
31.5
22.1 - 44.2
63
44.2 - 88.4
125
88.4 - 177
250
177 - 354
500
354 - 707
1,000
707 - 1,414
2,000
1,414 - 2,828
4,000
2,828 - 5,657
8,000
5,657 - 11,314
 

CENTRE FREQUENCIES FOR THIRD-OCTAVE BANDS

Centre Frequency
Centre Frequency
Centre Frequency
(Hz)
(Hz)
(Hz)
10
100
1,000
12.5
125
1,250
16
160
1,600
20
200
2,000
25
250
2,500
31.5
315
3,150
40
400
4,000
50
500
5,000
63
630
6,300
80
800
8,000


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