DAW: How does the mixing engine work?

Plug-in hosts and other software applications discussion
KVRAF
2033 posts since 6 Sep, 2005

Post Mon Sep 20, 2021 3:45 pm

I have a simple question:

How does the basic DAW Mixing engine works?

For example:

Track A volume is at 100%
Track B volume is at 100%

Why doesn't that bring the master to 200%?
What if you add 10 tracks?

How does the mixing engine manage that and avoid the playing the 10 channels becoming a one big mess?

KVRAF
1873 posts since 15 Oct, 2008 from Germany

Post Mon Sep 20, 2021 8:26 pm

Typically, the value of all channels is just added. Yes, when two channels currently have a signal at eg 0dB (that's what you probably mean with "100%"), the master would overload, ie go over 0dB. Because decibel is a logarithmic scale, the resulting total input into master would be +6dB. If there's nothing on the master channel that reduces this, the master signal would be clipped to 0dB.

Note btw that we're dealing with audio here, that is, cyclic signals going up and down, up and down. As a result, two channels playing at a fader setting of 0dB do not necessarily cause the master to overload to +6dB all the time. That would only happen if and when there's a moment at which both channels wave forms reach their maximum amplitude at the same time. That can happen, but does not necessarily have to, for example, if the two signals are perfectly phase inverted (that is, one signal's amplitude is at max when the other signal's amplitude is at min and vice versa). In that case, the signals cancel our each other and the master would receive -infinite dB (=silence)

Of course, in the background everything is just bits and bytes. The 0dB value is typically represented by a (64 bit or 32 bit) floating point value of 1.0. A floating point value of 0 is silence. Summing two channels with value 1.0 obviously gives 2.0 in total. Again, because the scale is logarithmic that would translate to +6dB.

A channel's fader just multiplies the output of a channel. A fader at -6dB multiplies the output by 0.5 for example. At -3dB the factor is 0.75. All the way down -inf dB the factor is 0.

I hope that makes somewhat sense. I'm sure other people here a better at explaining all that.

KVRAF

Topic Starter

2033 posts since 6 Sep, 2005

Post Tue Sep 21, 2021 11:21 am

Thanks for your reply Peter!

What I don't understand, is that in my DAW for example (or in any DAW really), all my faders are at 0db, I have 5 tracks, and the master never overloads. So is this only because none of them at 0db simultaneously?

So if all the 5 tracks hit a peak of 0db at the same time, the master would clip really hard?

KVRAF
21271 posts since 12 Jul, 2003 from West Caprazumia

Post Tue Sep 21, 2021 11:28 am

Having the faders at zero just means there is neither a gain increase nor a gain reduction being applied by the fader. It in no way means that the output of the channel is 0dBVU (Just imagine a channel whose source input is recorded silence.) To know the output of a channel you need to refer to the channel's VU meter.

KVRAF

Topic Starter

2033 posts since 6 Sep, 2005

Post Tue Sep 21, 2021 11:35 am

jens wrote:
Tue Sep 21, 2021 11:28 am
Having the faders at zero just means there is neither a gain increase nor a gain reduction being applied by the fader. It in no way means that the output of the channel is 0dBVU (Just imagine a channel whose source input is recorded silence.) To know the output of a channel you need to refer to the channel's VU meter.
Nice to know that! Sorry for lacking the basics.

So jens, if say all my 5 tracks for some dumb reason have audio at 0db (fader is at 0db as well), the master will overload?

I am just trying to understand if the master in a daw is just simple the sum of all tracks or if there is something else happening under the hood.

KVRAF
4728 posts since 17 Dec, 2009

Post Tue Sep 21, 2021 11:36 am

A3ntar wrote:
Tue Sep 21, 2021 11:21 am
Thanks for your reply Peter!

What I don't understand, is that in my DAW for example (or in any DAW really), all my faders are at 0db, I have 5 tracks, and the master never overloads. So is this only because none of them at 0db simultaneously?

So if all the 5 tracks hit a peak of 0db at the same time, the master would clip really hard?
If all 5 were in phase and same frequency, it would hit +24 likely
Image

KVRAF
21271 posts since 12 Jul, 2003 from West Caprazumia

Post Tue Sep 21, 2021 12:51 pm

A3ntar wrote:
Tue Sep 21, 2021 11:35 am
So jens, if say all my 5 tracks for some dumb reason have audio at 0db (fader is at 0db as well), the master will overload?
Yes, whenever more than one of them peak(s) during the same cycle.
I am just trying to understand if the master in a daw is just simple the sum of all tracks
It is.

KVRAF

Topic Starter

2033 posts since 6 Sep, 2005

Post Tue Sep 21, 2021 1:00 pm

OK, thanks for your reply all!

KVRist
110 posts since 14 Jan, 2020

Post Tue Sep 21, 2021 1:26 pm

Bear in mind that audio signals occur through time. summing two tracks isn't like adding the two largest peak values together, it's more that you're adding the value of both signals at every individual point in time, which means lots and lots and lots of simple sums. Those values can be positive or negative, so sometimes they get bigger when you add them together, sometimes they get smaller, at others they cancel out to 0. Then you take all those sums and plop them out one after another through time, and that's the two tracks added together.

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