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How to use phase cancelation to your advantage

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How to use phase cancelation to your advantage

Postby armans » Wed Nov 25, 2020 7:39 pm

I am working an acoustic song with only guitar, vocals, drums and bass. In the chorus there are two guitar parts playing different rhythms panned hard L and Hard R. Is it possible (and perhaps prefereble) to have some phase cancellation between the two guitars so that they are softer when the mix is summed to mono thereby not piling on top of the vocal and obscuring intelligibility? So it would go really wide in stereo and as a result the two parts are out of the vocals way then when summed to mono they partially cancel each other out and become softer allowing the vocal to be heard as well.

How is this best achieved? Would boosting the "side" channel in the chorus part of the stereo guitar bus work or can this cause problems? Or would double tracking by nature have some cancelation even if the two guitar parts are different (lets say picking L and strumming R)? I know from experience that the cancelation is always greater when the parts are more similar (maybe I need more experience :lol: so correct me if I am wrong) so in this case because the parts are playing different things it might not achieve what I am after.
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Re: How to use phase cancelation to your advantage

Postby CS70 » Wed Nov 25, 2020 8:05 pm

Hmm.. it shouldn't be necessary, because when you sum to mono, yes, the guitars will get louder - but so should all the rest! What you need to preserve is the balance so that it does not change dramatically when the stereo tracks get summed. That means essentially not having big phase issues in any track, so that the balance you hear in the stereo mix is more or less maintained (using m/s for stereo widening is actually a good way to achieve exactly that, btw).

In other words, if your voice gets overwhelmed by the guitars when summing L and R, the issue is more about the vocal track than the guitar track.

Sure, if all you have is guitar and vocals you might try to lower the guitars as well in mono, but if you had a slightly more complex mix, once you lower the guitars you would have to lower the drums, then the bass etc.

Usually you can afford "special effect" things to disappear or become less prominent in mono - for example wide stereo pads - but certainly not the vocals..

Some people mix in mono to get there.
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Re: How to use phase cancelation to your advantage

Postby Hugh Robjohns » Wed Nov 25, 2020 8:45 pm

armans wrote: Is it possible (and perhaps prefereble) to have some phase cancellation between the two guitars so that they are softer when the mix is summed to mono thereby not piling on top of the vocal and obscuring intelligibility?

It is possible, but it's definitely not preferable. For starters it would result in a radically different sounding mix in mono compared to stereo -- ie. it would have very poor mono compatibility. That means listeners in different situations hear wildly different mixes... And that's not considered 'a good thing'.

Secondly, having a lot of out-of-phase elements in the stereo mix can sometimes result in the material being rejected by some broadcasters -- and some listeners find it makes them feel I'll too.

...when summed to mono they partially cancel each other out and become softer allowing the vocal to be heard as well.

The problem you're trying to address is actually one of poor arrangement and/or poor sound selections. You're saying your guitar parts are trampling over the vocals in mono, and it only works in stereo because of the spatial separation.

This is quite a common problem, but the solution is to change the arrangement, so that the guitar parts don't play during the vocal lines, or change the timbre and tonality of the guitar parts (possible by using different chord inversions) so that the guitar parts don't sit in the same part of the spectrum as the critical voice elements.
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Re: How to use phase cancelation to your advantage

Postby armans » Thu Nov 26, 2020 10:19 am

Hugh Robjohns wrote:
The problem you're trying to address is actually one of poor arrangement and/or poor sound selections. You're saying your guitar parts are trampling over the vocals in mono, and it only works in stereo because of the spatial separation.

Yes but won't spatial separation always make the vocal clearer even if the arrangement is good? Having a good arrangement won't give you the same clarity as if those parts are panned out the way as well right? And what happens when both the guitar parts are summed to mono, don't they become louder against the vocal since you are summing the two parts together?
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Re: How to use phase cancelation to your advantage

Postby armans » Thu Nov 26, 2020 10:24 am

CS70 wrote:Hmm.. it shouldn't be necessary, because when you sum to mono, yes, the guitars will get louder - but so should all the rest!

Oh ok so if the vocal is centrally panned then in mono it too will become louder and the relative perceived volume between it and the two hard panned guitars will be relatively maintained? I don't know why but it just doesn't sound that way in my mix... :) It sounds like the width I am gaining in the chorus in stereo seems to cloud the vocal in mono regardless of the arrangments I have tried. I thought there could be some way to encode a mono version of my mix so that when the guitars get summed together they actually lose some perceived volume against the vocal in the mono version thereby giving me the best of both worlds. A wide stereo mix in the chorus and a mono sum that still has a good balance between the vocal and guitar parts (I don't mind that the guitars lose a bit of clarity amongst themselves)
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Re: How to use phase cancelation to your advantage

Postby Hugh Robjohns » Thu Nov 26, 2020 11:06 am

armans wrote:Having a good arrangement won't give you the same clarity as if those parts are panned out the way as well right?

Look at all the great records in the world... the best ones always rely on great arrangements rather than spatial panning! It's a fundamental building block!

And what happens when both the guitar parts are summed to mono, don't they become louder against the vocal since you are summing the two parts together?

Nope. Again, this is a fundamental element of audio recording science.

If your two guitar parts have a degree of incoherence (ie. they are not identical) -- which is an essential factor in a wide panned dual guitar effect -- when summed to mono those two parts will both add and cancel at different frequencies at different times as their phase relationships change. But at most, their overall summed mono level will only ever reach +3dB relative to each individual guitar part, and most probably won't go up much in level at all.

In contrast, anything panned central appears in both the left and right channels by definition, and so when summed to mono the signal amplitude doubles or rises by +6dB.

So a vocal should always end up at least 3dB stronger than sounds panned to the edge... Listen to any classic hit track and you'll always find the vocal becomes more prominent in mono, not less!

If, when you listen to the mono sum, a vocal is being trounced by the (previously) wide-panned guitars, then it's because the guitars are playing at the same time as the vocals and are either too loud or cover the same frequency range and thus mask the vocal.

The problem of playing at the same time can obviously be solved by tweaking the arrangement to add some space. The problem of too loud can be fixed with a tweak to the mix balance. And the problem of masking can be fixed by changing the character of the guitar sound or the actual notes/chords being played (or the character of the vocal sound).
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Re: How to use phase cancelation to your advantage

Postby CS70 » Thu Nov 26, 2020 12:09 pm

armans wrote:
CS70 wrote:Hmm.. it shouldn't be necessary, because when you sum to mono, yes, the guitars will get louder - but so should all the rest!

Oh ok so if the vocal is centrally panned then in mono it too will become louder and the relative perceived volume between it and the two hard panned guitars will be relatively maintained? I don't know why but it just doesn't sound that way in my mix... :) It sounds like the width I am gaining in the chorus in stereo seems to cloud the vocal in mono regardless of the arrangments I have tried. I thought there could be some way to encode a mono version of my mix so that when the guitars get summed together they actually lose some perceived volume against the vocal in the mono version thereby giving me the best of both worlds. A wide stereo mix in the chorus and a mono sum that still has a good balance between the vocal and guitar parts (I don't mind that the guitars lose a bit of clarity amongst themselves)

Most devices will convert to mono by summing the L and R channels, and this will obviously apply for all frequencies.. summing doesn't know or care if a frequency component comes from a vocal or a guitar :)

The most common reason (that I have seen) for vocals becoming overwhelmed in mono is that the VOX goes thru a stereo reverb or other processing which sounds wonderful... in stereo (I _love_ wide vocals myself!), while other tracks aren't subject to the same treatment. Your case might be the opposite, a stereo effect on the guitar that increases their level when the mix is summed to mono..

Cancellation often happens in specific frequency bands so it may be difficult to perceive on the soloed VOX bus.. when soloed, thing sounds okay-ish, but say in the mix the vox (when summed to mono) loses enough high frequency that (say) the guitars high-frequency components suddenly cover it. 80% of the vox is still there, but the 20% that now is not so prominent is the exact one which make our brain feel the voice is "on top".

There's a few ways to solve the issue - all involving some try and error and checking in mono. For example, if the culprit is a stereo reverb, one can use a ping-pong delay instead. You can process the reverb return. lowpassing it, or nudging one of the stereo channels to find a point where you still have a nice sound but there's much less cancellation in mono. You can use M/S to control exactly what the reverb does on the M channel (for example, you put FabFilter EQ in M/S mode on the reverb return and you make a low Q cut in the Mid only in the frequency band that is more affected). You can of course subject the other tracks to the same treatment.. and so on.

Another way is, as I mentioned, to first establish the balance in mono and then add panning and effects to make the stereo image nicer, but every time checking how the mono image responds (in terms of changing the balance and the timbre). That workflow makes sure that you don't make moves that work only in stereo. I don't use it myself, but I know people who use it consistently and it works well. Or of course, you avoid wide stereo effects altogether...

And of course as Hugh say the arrangement itself is a very important tool - a good arrangement is easy to balance and things don't need impressive stereo effects to sound good :)

In any case, mixing is primarily about balance - in mono and stereo, so once you have found the right one, you simply don't want to do any processing that changes it drastically in mono.
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Re: How to use phase cancelation to your advantage

Postby armans » Fri Nov 27, 2020 9:34 am

Hugh Robjohns wrote:
armans wrote:Having a good arrangement won't give you the same clarity as if those parts are panned out the way as well right?

Look at all the great records in the world... the best ones always rely on great arrangements rather than spatial panning! It's a fundamental building block!

Agreed

Hugh Robjohns wrote:If your two guitar parts have a degree of incoherence (ie. they are not identical) -- which is an essential factor in a wide panned dual guitar effect -- when summed to mono those two parts will both add and cancel at different frequencies at different times as their phase relationships change. But at most, their overall summed mono level will only ever reach +3dB relative to each individual guitar part, and most probably won't go up much in level at all.

In contrast, anything panned central appears in both the left and right channels by definition, and so when summed to mono the signal amplitude doubles or rises by +6dB.
Ok I think I get this

Hugh Robjohns wrote:So a vocal should always end up at least 3dB stronger than sounds panned to the edge... Listen to any classic hit track and you'll always find the vocal becomes more prominent in mono, not less!

Ok lets say those two guitar parts are very similar, like let's say they are double tracked guitar parts with the same frequency content, won't they reinforce each other in the mono mix and also be +6db louder? or is it because of those subtle phase differences that the mono mix of those two guitars will only be +3db and not +6db like the vocal?

Hugh Robjohns wrote:If, when you listen to the mono sum, a vocal is being trounced by the (previously) wide-panned guitars, then it's because the guitars are playing at the same time as the vocals and are either too loud or cover the same frequency range and thus mask the vocal.
Ok thanks for explaining this, very easy to understand when you say it that way, thank you
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Re: How to use phase cancelation to your advantage

Postby armans » Fri Nov 27, 2020 9:41 am

CS70 wrote:Your case might be the opposite, a stereo effect on the guitar that increases their level when the mix is summed to mono..

There are no effects on the stereo guitars at the moment but I was wondering, if, for example, I panned those two guitar parts hard left and right and sent them to a stereo bus, and using my fabfilter EQ plugin, I could increase just the level of the "side" channels relative to the "mid" channel to effectively widen the guitar parts in stereo and add more width. From what I understand about phase cancellation and summing those type of stereo effects in mono they should now effectively be much softer relative to the other elements in the mix in mono since I was only increasing the gain on the side channels and not in the middle and that gets cancelled out in mono.
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Re: How to use phase cancelation to your advantage

Postby Hugh Robjohns » Fri Nov 27, 2020 11:28 am

armans wrote:Ok lets say those two guitar parts are very similar, like let's say they are double tracked guitar parts with the same frequency content, won't they reinforce each other in the mono mix and also be +6db louder?

Nope. They have to be absolutely identical in amplitude and phase to sum perfectly and result in a 6dB boost. Any differences at all and the summation will produce a lower level.

Ok thanks for explaining this, very easy to understand when you say it that way, thank you

No problem! Glad it's helping.
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Re: How to use phase cancelation to your advantage

Postby armans » Fri Nov 27, 2020 12:48 pm

Hugh Robjohns wrote:
armans wrote:Ok lets say those two guitar parts are very similar, like let's say they are double tracked guitar parts with the same frequency content, won't they reinforce each other in the mono mix and also be +6db louder?

Nope. They have to be absolutely identical in amplitude and phase to sum perfectly and result in a 6dB boost. Any differences at all and the summation will produce a lower level.

Ok so then going back to my OP question, can't this be used to our advantage in some way. I mean, the more different the parts, the quieter they will be in mono right? And don't we ever need that in mono? In other words, have you ever needed something to be louder in the stereo mix but quieter in the mono mix?
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Re: How to use phase cancelation to your advantage

Postby Hugh Robjohns » Fri Nov 27, 2020 12:52 pm

armans wrote:I mean, the more different the parts, the quieter they will be in mono right?

We're only talking about a few decibels difference here...

...have you ever needed something to be louder in the stereo mix but quieter in the mono mix?

I'm always working hard to make the two sound as similar as they can possibly be.
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