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Topic Title: Measuring consumer line level audio with a VU meter
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Created On: 29 January 2014 07:14 PM
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 29 January 2014 07:14 PM
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jencam

Posts: 608
Joined: 06 May 2007

What is the correct way to connect up a VU meter to measure the loudness of consumer line level audio? That's the -10 dBV line level rather than the +4dBu professional line level. Is consumer line level sufficiently standardised to enable measurements or is it some pseudostandard that works 99% of the time?

A VU meter connected in series with a 3.6k resistor indicates 0 VU when driven by a 1kHz sine wave at +4dBu or 1.228V RMS. Does this resistor affect the ballistics of the meter movement and is essential to officially comply with standards?

If a VU meter is to indicate 0 VU when driven by a 1 kHz sine wave at -10dBV or 0.316V RMS from a consumer line level output, then an amplifier circuit is required to increase the voltage. Is there an officially specified input impedance for this amplifier?
 02 April 2014 02:54 PM
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RodneyDuggan

Posts: 5
Joined: 11 February 2007

Yes the 3.6k resistor affects the ballistics and these are quite rigidly defined in the VU standard, although many meters with VU scales don't attempt to be compliant. Proper VU meters tend to be quite expensive as a result of the tight specifications.
One definition of a VU meter is "if the needle is moving it's wrong", as they do miss showing peaks, however many expert audio engineers have developed a skill of correlating their hearing with the dynamics of an VU meter as a sort of poor man's loudness meter.
The correct way to show domestic level on the VU meter would be with a 10dB amplifier. Input impedance should not be too relevant as long as it's between about 1k and 10k so that you don't load down the domestic source, it's voltage we are measuring after all.
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