Recording before trigger
When Pre Trigger is higher than 0 then the wave signal starts to be recorded
before the first trigger. The period of such recording depends on the sample
frequency and bits per sample. The pre-trigger periods are:
• for 24 bits per sample: 2s for 48 kHz, 4s for 24 kHz and 8s for 12 kHz.
• for 16 bits per sample: 4s for 48 kHz, 8s for 24 kHz and 16s for 12 kHz.
4.5 SELECTING MICROPHONE COMPENSATION – COMPENSATION
The Compensation position is available only
in the Sound meter modes. It allows you to
select the appropriate compensation for
different measurement situations. Default
settings – see Chapter
2.8.
The Microphone compensation (microphone inner noise and thermal compensation) is switched on by default,
however it is possible and necessary to switch it off for electrical measurements (e.g., laboratory calibration
measurements).
The Free Field and Diffuse Field positions are intended to compensate the instrument frequency response in
the free field or diffuse field conditions. The microphone supplied with SV 977D is designed for sound
measurements in the free field conditions. The Free Field option means that the correction filter for the diffuse
field conditions is switched off.
The Windscreen compensation should be switched on if you use the SA 22 windscreen.
The Outdoor Environment and Outdoor Airport compensations are dedicated for the applications with the
use of the SA 277D outdoor microphone kit (usually when the instrument is working as a part of the SV 277
monitoring station). The characteristics of the outdoor filters depend on the dominating sound incidence angle:
environmental monitoring (incidence angle 90 deg) or airport monitoring (incidence angle 0 deg).
The frequency characteristics of all filters are given in Appendix C.
Note: When using windscreen SA22 the Windscreen compensation
filter must be switched on during windy conditions to maintain good
tolerances margin of the SV 977D frequency response.
Note: For the free filed measurements with the SA 277D outdoor
microphone kit the Outdoor Environment or Outdoor Airport
compensation must be selected.
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