Audio Channel Monitoring in the master section - question

I noticed in the “Audio Channel Monitoring” dialog, we have the following options:

  1. Default Channels
  2. Mix to Mono
  3. Mix to Mono (L-R)
  4. Left Channel Only
  5. Right Channel Only
  6. Mid Channel Only
  7. Side Channel Only

My question is this:

Aren’t #2 and #7 the same thing? If not, how do they differ? Also, #3, and #7. Aren’t they the same too? If not, how do they differ (I do notice a slightly different level for some reason)?


#2 collapses the stereo mix field to mono
#7 plays only the mid channel without any side information

So, if you play some very narrow material to begin with, these could sound similar. If you compare the two options with some very wide material, you’ll notice the difference between the two options more easily. Try some stereo Beatles mixes or the first Ramones album.

For #3 and #7 I refer to the manual:

Mix to Mono (L-R)
Mixes the stereo channels into mono channels and removes the right channel from the left channel. If both channels are the same, you hear silence. This allows you to check if the audio is true mono.

Side Channel Only
Mixes the side stereo channel into two mono channels.

The mid channel IS a collapsed stereo mix to mono: M = L + R

The side channel IS a collapsed stereo mix to mono: S = L - R

I’m confused… it seems like there are some redundant options here. These explanations do not clarify any significant difference that I can see.

@toader: You are right. But most users don’t know the underlying maths. Hence it’s better to have separate options. It’s clearer for most people.

There’s a pretty large level difference between #3 and #7 on files I tried. Exactly 6 db on files I tested.

@bob99: indeed, we have, to be exact:
M = (L + R) / 2
S = (L - R) / 2

Thanks PG. I guess I just still don’t understand why #2 and #6 are the same level and they’re identical, but #3 and #7 are different levels, but otherwise they’re identical (they null if you level match them by 6 db). If everything’s as it should be, and the first pair should be the same level, and the second pair shouldn’t, I guess I’ll get it eventually, but right now I’m just trying to wrap my head around that level difference only in the second pair. If M = /2 and S = /2.

To prevent likely clipping, WaveLab reduces the gain by -6dB wit “Mix to Mono”.

But if #3 and #7 are technically the same? Why is the level only reduced on one of them? It should probably be reduced on both…

Generally, left and right signals are much in phase (!). Hence doing L + R is likely to clip. Hence it is better to extract M / S by decreasing the signal by -6dB.
But clipping is not an issue when doing L - R, hence no need to apply a gain of -6dB here.

This whole thing is kind of weird. What I think would be more useful is this:

Sum Stereo To Mono (to check mono compatibility of stereo image)
Mix To Mono L-R (Mix To Mono While Phase Inverting The Right Channel)
Left Channel Only (simple)
Right Channel Only (simple)
Mid Channel Only (No sides channel information)
Sides Channel Only (No mid channel information)

To my, Mix To Mono and Mid Channel Only should not be the same thing.

Mix to mono should include the entire stereo field but mixed to a mono stream to check mono compatibility.
Mid Channel Only should simply remove the side channels.

The Brainworx bx_control V2 plugin is a good model for what is useful:
brainworx bx_control v2 free download

Aside from the level changes within the plugin of course…just the channel selections.

They are the same thing. That is all a “Mid” channel is - It is only the left and right mixed to a mono stream. This is exactly how you remove the side channel… there is no other way. This is the same as M = L + R

A “Side” channel is the exact same thing, but with either the left or right side phase flipped before they are added together. The phase flip makes the + in to a - sign… This is exactly how you remove the mid channel… there is no other way. This is the same as S = L - R

You can also do the exact same thing in the analog domain. I see you have a Cranesong Avocet. Listen to a stereo mix, and hit the mono button. Both the left and right channels are now being added together in the analog domain so you hear it as mono. You are listening to the “Mid” channel. Technically, you’re hearing “dual mono” - the Avocet is sending an identical mono signal to both speakers rather than just one speaker. If you look at my studio pics, you’ll see I have one Auratone in the middle. This way, I can monitor with true mono (only one speaker), and not dual mono (my other speakers are still dual mono though). Now while listening in mono, hit the phase button. The Avocet retains the mono signal, but it will now flip phase on one side of the stereo mix prior to the mono conversion. This all happens at light speed, and you are now listening to the “Side” channel.

Wavelab is doing the exact same thing digitally, and technically, M-S techniques are probably even more perfect in the digital domain.

I agree - this definitely makes sense. However, #3 and #7 are both doing L-R, so it’s strange that they aren’t the exact same level.

Yes - this is what I’m talking about. #3 and #7 are both doing L-R - it seems they should be identical in level.

Yes, thanks for the info. I suppose I need to think about this more when I have more time but part of the reason I never really use these settings in WaveLab is because I can do most of that on the Avocet which is great.

I agree, If the other mono’s got reduced 6 db as PG said, it seems #7 got reduced 12 db somehow. I’m going to go through auditioning all the stereo’s and mono’s later, but I’m guessing #7 will probably sound noticeably quieter than the others. But until I audition I’m just guessing.

However, #3 and #7 are both doing L-R, so it’s strange that they aren’t the exact same level.

S = (L - R) / 2.
The -6dB is necessary to match the same logic as for the Mid signal (L + R) / 2

Sorry Philippe, I feel like I could drag this out forever because I still don’t get it.

Is this correct? :

#2 Mix to Mono = L + R
#3 Mix to Mono (L-R) = L - R
#6 Mid = (L + R) / 2
#7 Side = (L - R) / 2

So why are #2 and #6 the same level?

#2 Mix to Mono = (L + R) / 2

Ok then it’s:

#2 Mix to Mono = (L + R) / 2
#3 Mix to Mono (L-R) = (L - R) / 2
#6 Mid = (L + R) / 2
#7 Side = (L - R) / 2

#2 and #6 are identical and are the same level.
#3 and #7 are identical and should be the same level, but they’re not. #7 sounds 6 db too low.

Or is #3 not divided by 2 ?


#3 Mix to Mono (L-R) = (L - R) / 2

No, #3 Mix to Mono (L-R) = (L - R)