Phase....What is it????

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Spider

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hi there everyone , im a little new to recording and i seem to hear everyone talking about things sounding 'out of phase' and even people recording something 'out of phase'... could someone please clarify this for me as im a little unsure as to what its all about ... I know its got a lot to do with L + R positioning ... but im still a little unsure .. any help would be great ... thanks all...
spider
 
It's a small world... someone else from Perth!

Now then phase.... have you ever noticed when you are sitting in your car at the traffic lights wanting turn to right... your indicator light never matches the car in front of you... you sit there watching it and sometimes they flash at the same time but then get out of sync... then they'll flash at the same time again and so... well, this is exactly what's going on with sound when you hear people say "it's out of phase".

Sound waves are much like water waves... you have peaks and troughs... if you are stereo micing something you want to make sure that the peaks and troughs line up for both mics... if they don't then they can "cancel" each other out. To remedy this you could move one mic forward or back from the source just enough so that they are in phase, but generally because the distance between a peak and trough is pretty small (and because sound engineers are lazy pricks) someone invented the "Phase Button" which flips the peaks and troughs about so that where there was previously a trough there is now a peak etc... hopefully remedying the out of phase problem.

Hope this helps!
 
hi there cooperman , hey thanks a lot for that i kind of see what you mean .. Im glad u explained it like that , was much easier to understand.
 
Hey Cooperman, don't forget that the wavelength changes with frequency, so if more than one tone is emitted changing source position won't make all sounds out of phase. That's probably the "official" reason there is a phase button. Engineers are still lazy -- but I'm thankful they are.

A point of clarification for Spider:
If things are completely out of phase (often referred to as 180 degrees out of phase) you will hear no sound. The shimmering sound we usually associate with phasing is due to the source starting in phase, moving completely out of phase, and back again very quickly.

Physics is phun...

MikeDog
 
hey thanks for those links ed , very interesting , looks like i have some heavy reading ahead of me ....
just a quick question , so is it possible to visually see if a sound wave is out of phase... my guess is yes , just wondered what you guys reckon..??
thanks all.....
spider
 
I am sure you could, but for recording purposes, it is not really neccessary. You can easily check to see if two mics are in or out of phase with each other by simply reversing the phase on one of the mics. If when you flip the phase, the sound get thinner sounding, the mics were in phase before reversing the phase on one of them. If the sound gets fuller (listen for the low end to seem to get louder), then the mics were not in phase before you reversed the phase on one of the mics. In this case, leave one of the mics reversed phased.

Ed
 
hey thanks for that fellas...
hey ed , when you say reverse the phase , are you talking as in left and right ???? could u explain exactly what you mean .. a little lost thats all..
cheers..
Spider
 
My ART Tube MP has a phase reversal button. Push the button, and the unit reverses the phase. You can't make a mistake with it, because the sound difference is so obvious.
 
Spider...they are all wrong. A phase is something your attitude goes through when you turn thirteen.
 
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