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eitw
12-03-2014, 02:04 AM
I'm sure there is a perfectly good reason for this but.... try this:

Setup a Mono track with a Signal Generator (1k Sine @ -20dB).
Bus it to a Mono Aux (Send fader normalized).
The Aux loudness meter will read -20dB.
All good so far.

Now, do the same thing but bus the mono signal to a Stereo Aux.
The Stereo Aux loudness meter will read about -6dB less (-3dB per channel) than the original -20dB test signal that was sent.

If a Square wave is used it will still be -20dB.

How do you explain the attenuation happening when going from Mono to Stereo using a Sine wave in this situation?

Is this Black Magic or Science?

crizdee
12-03-2014, 04:45 AM
I'm sure there is a perfectly good reason for this but.... try this:

Setup a Mono track with a Signal Generator (1k Sine @ -20dB).
Bus it to a Mono Aux (Send fader normalized).
The Aux loudness meter will read -20dB.
All good so far.

Now, do the same thing but bus the mono signal to a Stereo Aux.
The Stereo Aux loudness meter will read about -6dB less (-3dB per channel) than the original -20dB test signal that was sent.

If a Square wave is used it will still be -20dB.

How do you explain the attenuation happening when going from Mono to Stereo using a Sine wave in this situation?

Is this Black Magic or Science?

Yeah its black magic science and the pan law


Chris

mesaone
12-03-2014, 10:10 AM
Check this out for Pan Law info: http://duc.avid.com/showpost.php?p=1695396&postcount=15

DC-Choppah
12-03-2014, 06:58 PM
Each of the stereo signals will reach your ear in phase (assuming you are sitting right at the center).

When two signals add up coherently you get a 6 dB boost, so you are back to where you started.

Since the DAW designer knows this, they subtract the 6 dB so that you perceive no net volume change as you go from mono to stereo.

The 6 dB pan law is the most extreme and theoretically correct for your sin wave and only when you sit exactly in the center. In reality the sounds add incoherently somewhat (since the speakers are not matched) and also you do not sit at the exact center. So there are other pan laws, 4 dB , 3 dB etc.

There are different standards in different industries actually.

eitw
12-04-2014, 12:28 AM
Thanks for all the great info guys. Makes perfect sense now.

And I'm guessing that the Square wave still registers -20dB because it is constantly peaking all the way at the top of the waveform or all the way at the bottom.

This accurate?

simon.a.billington
12-31-2014, 02:37 AM
Pan law indeed.

Fundamentally, it so that when you pan a signal across the stereo field their is no perceivable loss in volume. It can be a handy thing.