An interesting issue came up when a friend was mixing down his mono tracks through a stereo aux to his stereo master. The was a noticeable drop in volume by 3-4 dB which I find very strange.

Can anyone identify why this would occur as I simply cannot put my finger on it. The metre was at 0 on both the aux and master channels so this is not the issue.

Has anyone encountered this before?


  • Which Program did you use? – Tobias Schmidt Nov 4 '13 at 10:55
  • What is the volume drop relative to? ie the volume only drops routing through the Aux but is louder when routed to the Master only? – Brendan Rehill Nov 4 '13 at 11:16

Did the volume drop or level drop? Two totally different things. If it's the level that dropped, Well, the mono signal (on a mono meter) will drop by that much across stereo meters because of how the signal is distributed.

Double in energy = 3dB. Cutting a signal from one to two channels evenly means that each side of the resulting signal will be 3dB lower - again not the volume but the distribution of energy (across multiple channels vs a single channel)

When you bring the stereo file back in, split to mono, send both tracks to a mono aux, pan hard center and play both - because the signal is in phase, both signals will sum +3 dB to the original level across the aux.

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  • Hold on. Adding two uncorrelated signals with identical level results in a +3dB increase. Adding two correlated signals (if they are the same, that's maximum correlation) with identical level results in a +6dB increase. Routing a mono signal to a stereo bus will not automatically result in a -3dB level, it depends on how the DAW handles this (similar to choosing a panning law): if the signal is duplicated to left and right, there is no drop. If the energy is spread out from one to two channels (like you indicate), then there will be a drop. – EMV Nov 7 '13 at 6:03

Can you give us some more information as to how he was performing this activity? Analogue mixing desk or digital DAW? If so - which one? Depending on the content of the mono tracks I can easily demonstrate mixing two mono tracks containing tone into a stereo track and have Zero output. All depends on the phase of the incoming signals and how they interact with each other.

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  • We are using a 003 through PT 9. But I agree with both you and Stavrosound. It seems to be more of a volume situation but also the fact that some phasing is happening. We are working on it as I write. Thanks – oinkaudio Nov 4 '13 at 10:22

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