Phasing issues

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cowparsleyman

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« on: August 29, 2018, 07:36:10 AM »
I know very little about this topic...and I kwo there are some really clever folk out there who can help....

So much questions are
what is it?
why does it happen?
how can you spot it in a mix?
what can you do about it?

Thanks in advance

cpm

Ramshackles

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« Reply #1 on: August 29, 2018, 11:37:11 AM »
Phasing issues occur when you have a stereo source (e.g. two mics on a guitar) which has a timing difference (it is not in phase). This causes the 2 signals to partially cancel each other out. Sometimes,  the cancellation is not consistent through time, so you get this phasey effects - this is exactly what a 'phaser' plugin does to your audio; it duplicates another channel and varies its phase.

You can check whether your stereo signal is in phase in your DAW. Zoom in on the L&R channels of your audio so you can clearly see the waveform. If the peaks and troughs of both channels occur in the same place, you are in phase. If one channel is offset, it is out of phase.
If you notice phase issues when recording, the solution is to shift one of the mics a little (there are plenty of diagrams and even apps out there showing you angles and distances to avoid phase issues), or even to flip the phase switch on one of the mics (if they are drastically out of phase).
If you don't notice till mix time, you can often simply nudge one of the channels forwards/backwards until they line up.

It's always worth going through your mix and checking for phase issues!

If you want to train your ears to listen for phase issues, just load up the same mono track twice in your DAW and experiment with nudging one of the tracks in and out of phase. Listen to the result.

Ramshackles

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« Reply #2 on: August 29, 2018, 11:50:31 AM »
More complex phase issues

You can get phasing issues which are more difficult to get rid of due to reflections in your recording room.
When you sing into a mic, the majority of the sound goes directly into the mic. Some of the sound will go indirectly into the mic, first bouncing off a wall/window, floor or ceiling. This sound will arrive delayed and therefore you can get cancellation. It is a problem in relatively small rooms with no treatment and is usually referred to as 'comb filtering', since complete phase cancellation occurs at various frequencies across the spectrum - if you open up a frequency analyser on your track, it looks like a comb :D. Big troughs at regular intervals between the peaks.

Obviously, close-miking will mitigate some of these effects since the direct signal will be much louder than the indirect one. However, you don't need to get too far away before it becomes a problem.
I found an old sound-on-sound article referring to guitar cabinets which said:

"
If the distance from the cabinet's speaker cone is only six inches, and the floor is a foot below the mic, the direct and reflected sounds of the cone will meet at the mic capsule with around 1.5ms delay between them. In theory this will give a comb-filtering effect with total phase cancellation at around 300Hz, 900Hz, 1.5kHz, 2.1kHz, and so on.
"

This is assuming that the reflected sound is more or less identical to the direct sound, which of course isn't the case in the real world, so you never see total cancellation, which is why the effect can be difficult to spot.
But, you can certainly here the difference once its been pointed out and corrected!

You can't really treat this kind of phase problem in the mix - the only reliable remedy is acoustic treatment. A blanket behind the singer can work wonders.

Bill Saunders

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« Reply #3 on: August 29, 2018, 05:23:23 PM »
Hi Ramshackles

Thank you for the best explanation I’ve ever read about phasing issues - crystal clear!


cowparsleyman

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« Reply #4 on: August 30, 2018, 11:02:05 AM »
Hi Ramshackles

You did it again, really top notch explanation. I use a mic reflection booth to reduce the risk of these reflections, and tend to be quite close to the mic when I sing, so I don't normally experience phasing issues, but I think, there might be a bunch going on, could this happen by copying and pasting tracks, and shifting them a few ms to create a double tracking effect, but the phasing between the peaks of each Mono track would still be the same wouldn't it?

I have to be honest sometimes I click the phase button, just to see if it sounds better/different and yes sometimes, to my ear it does sound better, but I wouldn't know why! I think I did this on an acoustic track with MS mic'ing, and the 2 tracks just sounded 'thin and weedy', clicked the phase button on one of the tracks and bingo, it sounded more colourful, but I could also keep it like that if I wanted that particular weedy sound I guess.

Thanks again.

cpm

Boydie

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« Reply #5 on: August 30, 2018, 03:38:13 PM »
Quote
I did this on an acoustic track with MS mic'ing, and the 2 tracks just sounded 'thin and weedy', clicked the phase button on one of the tracks and bingo, it sounded more colourful, but I could also keep it like that if I wanted that particular weedy sound I guess.

That is a classic cause and symptom of phase issues

@Ramshackles did a fantastic job of explaining "phase" without the use of a waveform diagram

Here is an article with wave diagrams to help understand and recognise phase issues when zooming in to waveforms on your DAW:

https://www.uaudio.com/blog/understanding-audio-phase/
To check out my music please visit:

http://soundcloud.com/boydiemusic

Twitter: https://twitter.com/BoydieMusic

Ramshackles

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« Reply #6 on: August 30, 2018, 04:46:03 PM »
Nice link @Boydie; its a very clear article.

could this happen by copying and pasting tracks, and shifting them a few ms to create a double tracking effect, but the phasing between the peaks of each Mono track would still be the same wouldn't it?
Small amounts of delay won't make much audible difference. If you have two mono tracks of the same source, both panned hard L and R and you introduce a delay - 10ms or so, you create something known as the 'haas effect', which gives the impression of greater stereo width. Those stereo widening tools in most DAWs use this (among other techniques I think). You have to be careful with such an effect because if you go too wide (too much delay), when you collapse to mono you could have some nasty cancellation.
Mono compatibility is still relatively important I think....

cowparsleyman

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« Reply #7 on: August 31, 2018, 11:29:14 AM »
@Boydie - Thanks Man - cool article, even I can understand it...

@Ramshackles - Blimey - the 'Haas effect', could be the next Album title...I'll keep an eye out for that in future, to be fair I don't use the 'copy and move it a long a bit' delay technique that often, only when I like the Vocal take and I want to thicken it without going to a doubler, or adding another track, especially when the line is particularly difficult to sing, or it's going out of my range, one risks the misalignment of the phrasing of the lyrics, so sometimes I might melodyne the original take and move it very slightly to create a harmony track...

Anyways thanks gents, really appreciate it.

cpm

Cawproductions

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« Reply #8 on: August 31, 2018, 03:57:03 PM »
Very interesting read guys, Loads of info.

Always learning something.

I have been playing around with the vocals space for about a month now, adding reflectors, using compression on the way in etc...

Finally locked down all the reflections in the (vocal Booth!!!), makes working with the vocal signal a lot easier...Just need to learn to sing now, can blame the gear...lol

Cheers Guys.

cowparsleyman

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« Reply #9 on: September 16, 2018, 12:46:44 PM »
Very interesting read guys, Loads of info.

Always learning something.

I have been playing around with the vocals space for about a month now, adding reflectors, using compression on the way in etc...

Finally locked down all the reflections in the (vocal Booth!!!), makes working with the vocal signal a lot easier...Just need to learn to sing now, can blame the gear...lol

Cheers Guys.

Whato @Cawproductions - A great vocal booth works wonders, how did you nail the issue in the end?

Aaaah singing, there's a thing, I wail like a howlin' wolf...or I reach a note and bingo! it's right on the cusp of where I can't sing, and sounds awful, I know @Cazrolina - can tell us a thing or two about how to sing....

now where's that gear mag....

cpm

Cawproductions

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« Reply #10 on: September 16, 2018, 01:35:46 PM »
Hi CPM.

I have a vocal surround, but found I was getting reflections and room noise from behind me when I sing (using the term loosely).
So, I turned the vocal surround so one side of me was the wall. I have a few homemade sound panels, One I fixed directly overhead on the ceiling and fixed one behind me to catch any reflections flying over my shoulder. There was one on the wall already. Then what I had left was a space to the left side of me. fortunately my room is treated so that tamed some of these stray waves.

I noticed a massive difference once I started to process my vocal, all those strange room sounds were gone so did not get amplified in the process chain.

After a few reads, youtube videos and test recordings,  I have found the brightness in my mic (Rode NT2a) to be around 2.5 - 3K so I now use the onboard DSP compressor and EQ on my focusrite DSP 24 pro make a small EQ cut and slightly compress on the way in. Previously always done this after recording...I think it is a marked improvement.

The end result a much better starting signal to work with. I know a lot of guys record through some sort of channel compressor limiter (outboard) before it hits the interface, I may adopt this later.

Hopes this helps, been a trial and error game.

Cheers
Andy

cowparsleyman

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« Reply #11 on: September 16, 2018, 05:06:24 PM »
hi @Cawproductions - thats interesting, i have the same mic, and yes it does sound a tad bright-ish but I find it suits my voice, as it's a bit dull, so I use that to my advantage.

Thanks very much for sharing that, I'll certainly bear that in mind.

cpm