Stereo to Mono downmix attenuation amount?

I am asking about this because of a question that came up elsewhere, and I don’t feel I got a clear response about this anywhere, and the manual is deeply unsatisfactory on this topic (unless I missed something).

The question is what we are supposed to see when routing stereo into mono, considering default downmix settings(?) and pan law(?).

To recap where we left off:

Ok, the above is clear enough, but not when I measure it. To test I did the following:

  1. Create mono output.
  2. Create stereo audio track, insert test generator on it, set it to sine @ -9dBFS.
  3. Route stereo audio track to mono output.
  4. Set metering to “input”.

Now, here’s what I see on the mono output channel meter with respective pan-laws;

pan law / input

-6____ -9dB
-4.5__ -7.5dB
-3____ -6dB
0_____ -3dB
equal_ -6dB

So, if pan law has nothing to do with going from stereo to mono, and only a default 6dB downmix attenuation applies, then why are we seeing a different value at the input of the output channel?

Can people here confirm that the above is what they see as well, and can someone please explain the behavior?

It seems to me as if pan law indeed does change what happens to a signal as it leaves a stereo channel and goes into a mono channel, and it’s not a downmix preset that’s used (or maybe correctly - the pan law becomes the downmix default for the project). It’s as if pan law is applied to the independent left/right channels within the stereo channel.

For reference, from the Nuendo 6 manual:

Stereo Pan Law

In the Project Setup dialog, in the “Stereo Pan Law” pop-up menu you can select one of several pan modes. These modes are required for power compensation. Without power compensation, the power of the sum of the left and right side is higher (louder) if a channel is panned center than if it is panned left or right.

To remedy this, the “Stereo Pan Law” setting allows you to attenuate signals panned center by -6, -4.5, or -3 dB. Selecting the 0 dB option turns off constant-power panning. Experiment with the modes to see which fits best. You can also select “Equal Power” on this pop-up menu, which means that the power of the signal remains the same regardless of the pan setting.

This changed and now Nuendo 8’s manual states:

Stereo Pan Law
If you pan a channel left or right, the sum of the left and right side is higher (louder), than if this channel is panned center. These modes allow you to attenuate signals panned center. 0 dB turns off constant-power panning. Equal Power means that the power of the signal remains the same regardless of the pan setting.

When routing a track(with more - or less) channels to a bus, Mixconvert is automatically applied.
Mixconvert applies 3dB of attentuation. Why only 3dB? Because summing two NON-corrolated signals result in a 3dB increase of level.


Then why does the meter on the “receiving” channel show different values when set to “input”?

Did you try this yourself?

Anyone else?

I see conflicting information on this (such as -3 or -6dB downmix, pan law changes things or doesn’t), and all I want is to know what the intended and actual behavior is.

I would have to check again tomorrow. But is this again the awful Normalise=on as default again on the mixconvert? The most stupid concept from Steinberg devs ever… most of the time they are indeed brilliant but that was so awful I had to create a whole workflow to get around it in the past. I haven’t seen it for a whole or now though.

To check open the mixconvert instance and check if normalise is enabled or not…

I must have missed a “Normalize issue” then. This doesn’t seem to be that though, unless I’m missing something. I’m not in front of Nuendo now and won’t be until the weekend, as I’m on PT until then. So I can’t check “mixconvert”.

Where do I open that instance though? I’m not instantiating any plugins when I do this. I’ve always only done direct routing for mixes and stems and set it to equal power panning and it’s been fine.

If you use direct routing there shouldn’t be an issue really but you need to be aware of the default downmix choices preset by Steinberg. Explanation was available in the old manual. I have yet to look at the modern online version
If you use sends or regular routing the mixconvert will replace the panner for that signal path.

Yes, but as I wrote in that first post if my signal coming out of a stereo track is only subject to automatic downmixing then that would give me one level after that stereo channel, regardless of panning, correct? So I would think that routing a stereo channel into a mono output would yield downmixing and not depend on pan law. I mean, maybe I’m wrong about that, but that’s how my brain interprets it if someone tells me there’s no pan law when there’s downmixing, and there’s downmixing when going from stereo to mono.

But as I said, if I set my meter to read “input” and look at the output channel that receives the stereo track’s output then then level will change depending on the pan law I’ve set.

PS: I’ve avoided to use any direct outs other than the first slot, which then mimics the ‘other’ output (and I still think it’s a dumb, dumb idea to not make all direct outputs subject to the same rules).

You’re up early btw…! Got kids or insomnia?