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Old 16-08-2017, 01:53 PM   #1
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PHASE

HELLO

I am recently trying to learn a bit more in detail recently of production and have come across a subject that complexes me. This is phasing. I don't mean to use the audio effect phaser but the thing that happens when to wave forms collide and create phase. It seems this is important to understand especially with bass heavy music with a repetitive kick drum. Can anyone here start me off with some wee nuggets of knowledge to get the ball rolling.

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Daniel

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Old 16-08-2017, 05:53 PM   #2
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Re: PHASE

The phase of a waveform is where it is in it's cycle. Put really basically, it's how far along it is (time) and how positive or negative it is (amplitude). That's a gross generalization for 2D wave forms ie audio, but it can be extrapolated to complex or higher dimensions as well (light, quantum effects, etc).

The other thing you need to know is that two or more wave forms add their amplitudes via the wave superposition principle. This is basic math: if at a single point in time, one wave is at +1 and another one is at +1 at the same time, played together they'll be at +2, double the amplitude. That means that if you perfectly duplicated a track, it'll just be twice as loud (amplitude 2 instead of 1).

If you have one wave at +1 and one at -1 they add just like basic math: +1 -1 = 0. That's phase cancellation. So if two wave forms with opposite phase get played at the same time, they sum to zero and you get silence. They cancel each other out.

In the real world, there's only two places you usually get total phase cancellation - exact duplicates of tracks and things like basic wave forms (sine waves, etc), which is why you have to watch out for things like sub bass. Most wave forms are complex enough that you'll only get partial cancellations. If you play a guitar part and then play it again and flip the phase, they'll be close but not exact. Big chunks will cancel and you'll be left with a very weak, thin signal. This happens with recorded drums a lot, where the overheads will be out of phase and won't cancel completely but will be very weak until you flip the phase on one channel.

What's happening in partial phase cancellations is that either some tiny little bits (samples) are getting cancelled and others aren't, or you have one sample at, say, +36 and another one at -29 so that frequency gets cut to +7 instead of the loudness it had.

There's lots of resources online:

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would be good starting points. If you want to understand the nuts and bolts of why these things happen and the math behind them, any introductory Physics text will have a section on waves and superposition, and any decent Functional Analysis text will go over the math behind what's happening. I could recommend some specific texts, but it's more than most people want to mess with and certainly isn't necessary to understand what's going on in recording.

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Old 16-08-2017, 06:04 PM   #3
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Re: PHASE

Quote:
Originally Posted by Artificer View Post
If you have one wave at +1 and one at -1 they add just like basic math: +1 -1 = 0. That's phase cancellation.
This is literally all you need to understand phase cancellation.

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