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Voltmeter dB

Controls: Options >> Voltmeter >> dB
Macro: VoltMode=dB

Voltmeter dB mode is essentially the same as RMS mode, except that the value is reported in dB form. All the same Trigger considerations apply.

If the selected channel is uncalibrated, the dB value is given relative to full scale on the current range.

If the channel is calibrated, the dB value is relative to 1 volt, including Full-Scale Range and External Gain settings.

If User Units is active on a calibrated channel, the reported dB value is relative to one User Unit, so it also includes the Units/Volt factor.

If User Units is active and the units are Pa (Pascals) with the SPL button selected in the User Line dialog, the reported value is in SPL and is labeled as such.

Note that this SPL value will not be as accurate or as useful as that obtained with the Sound Level Meter option, because the Voltmeter acts in the time domain and thus does not use any Weighting Curve. More importantly, it does not use any frequency response information from the microphone calibration (.CAL or .FRD) file. If the .CAL or .FRD file specifies a certain dB correction at the current signal frequency, then the Voltmeter SPL reading will be off by that amount.

For bursts or other dynamic signals, there may also be differences due to the Voltmeter Time Constant versus the Response Time settings of the Sound Level Meter.

Despite these shortcomings, you may still find the Voltmeter SPL reading useful in addition to the Sound Level Meter, in certain cases where you need to read a second channel at the same time, and where you can compensate for the differences.

The Voltmeter allows you to set a relative zero dB reference via the dB Ref button. When this is active, all readings are relative to the reference value instead of 1 volt or User Unit, or the SPL reference pressure. The reported value is always shown in dB, even if SPL would otherwise be shown.

Macro Notes:

VoltMode=dB or VoltMode=4 sets the Voltmeter to dB mode. See Macro Notes under Voltmeter RMS for the complete list of mode names and numbers.

See also Voltmeter, Voltmeter Channel, Sound Level Meter


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