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Does the VU meter on commercial audio amplifiers measure the level of the input signal or the level of the amplified signal?

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  • \$\begingroup\$ I guess it must measure the signal level at the output of pre-amplifier, to determine whether this signal may saturate the power amplifier. \$\endgroup\$ Aug 13, 2014 at 17:58
  • \$\begingroup\$ @Tinchito is that speculation or backed by some source? I don't know the answer either but "I guess" isn't very convincing \$\endgroup\$
    – Funkyguy
    Aug 13, 2014 at 18:07
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    \$\begingroup\$ What manufacturer is still putting VU meters on their products in 2014? \$\endgroup\$
    – Matt Young
    Aug 13, 2014 at 18:08
  • \$\begingroup\$ @Funkyguy This is speculation, why not generated a response. Since usually a VU shows signal levels that saturate the amplifier, I think the most suitable place would be at the output of pre-amplifier. \$\endgroup\$ Aug 13, 2014 at 18:24
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    \$\begingroup\$ @Matt You probably won't see VU meters on a commercial power amplifier (they will have power meters); but you will see them on things like limiter/compressors, effects processors, etc. \$\endgroup\$
    – JYelton
    Aug 13, 2014 at 19:08

2 Answers 2

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A VU (volume unit) meter is meant to show the signal level, not the amplified level. If it measured the output level, it would be almost useless at any volume setting other than maximum.

A VU meter is meant to show when audio signals clip, so you can reduce amplitude. This is especially important when mixing and mastering audio, as you need headroom for post processing effects like reverb and compression.

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  • \$\begingroup\$ Yes, but is that really made this way in the amlifiers I can buy in the store? (I haven't ever bought one, that's why I do not know that by myself) \$\endgroup\$
    – v_2e
    Aug 13, 2014 at 19:09
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    \$\begingroup\$ @v_2e The same principle should apply to any amplifier, consumer or professional. If there's a VU meter, it will be for signal level. Power amplifiers and such will have a power meter or an LED to indicate clipping. It's fairly rare to find VU meters on home receivers or amplifiers these days. \$\endgroup\$
    – JYelton
    Aug 13, 2014 at 20:14
  • \$\begingroup\$ So, maybe I just confused the VU meter with the power meter? What I oritinally meant was the two rows of LEDs bouncing along with the music. \$\endgroup\$
    – v_2e
    Aug 14, 2014 at 8:20
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I use VU meters and they indicate to me the level at which clipping of an audio/music signal is likely to be occurring in the system/amplifier so, in your amplifier it doesn't matter where it is connected to, providing it correctly represents the potential overload point of your amplifier.

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It is generally recognized in the music industry that the peaks of music are usually about 6dB higher than the average level (which the VU meter reads) and hence -3VU is appropriately positioned in the middle of the scale.

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