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Sound Level Meter Peak / PeakTC Hold
The Sound Level Meter continuously monitors peak values, with and without response time constants, since the last Reset. The Peak and PeakTC buttons only select the display mode; you can toggle them on or off to see peaks or current SPL with no effect on the held values.
PeakTC shows the maximum SPL value, including both Weighting and Response. Response settings with long Attack times reduce the maximum SPL measured on transients, so PeakTC will be lower than Peak in many cases.
If both Peak and PeakTC are off, the display shows the current instantaneous Response output with full dynamics.
Peak and PeakTC maxima are computed and held separately, so you can view either of these or the instantaneous display at any time. The held values will always be updated whether you are viewing them or not. Reset always operates on both held values.
Note that Peak and PeakTC values are maintained separately for each Channel, but they are only updated when a channel is selected for SPL display. You can switch between channels and view peak SPLs from the last time that channel was shown, but you can't see what peaks may have happened in the meantime. All channels are cleared on Reset.
Peak and PeakTC measurements may also be made on .DQA file data recorded on a calibrated system. Alternatively, you can use .WAV or other uncalibrated files by opening the User Line dialog and loading a calibration file, or by setting Units Name to "Pa" and setting the proper dB:Units/Volt, then toggling SPL on.
If you set a low Read Step Size in the DDisk Controls dialog, and toggle Trigger off, you can get a "slow motion" playback of the file that still retains the specified response time dynamics for PeakTC.
One application for Peak Hold is determining vehicle pass-by noise, where the passing vehicle sound is much louder than the background. By capturing the peak, you can read the value at leisure after the test. (See also the Spectrum Analyzer Peak Mode topic for a discussion of how to measure specific frequency regions, which can be done instead of or in conjunction with the Sound Level Meter.)
SPLpeak=1 activates Peak display mode, SPLpeak=0 returns to instantaneous SPL display, and SPLpeak=x toggles between these.
Similarly, SPLpeakTC=1 activates PeakTC display mode, SPLpeakTC=0 returns to instantaneous SPL display, and SPLpeakTC=x toggles between these.
See also Sound Level Meter
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