Checking Phase When Recording Multiple Guitar Amps

[brandondrury]

Right on...question??? Can I check the phase at the output of the mike's by using a signal generator at the front end of the amps and then switch pins 2 and 3 (or is it 1 and 2) at the output of the mikes to match polarity?

In layman's terms, switching those 2 pins around should be the same thing as pushing the polarity button on a preamp or even on the channel strip on a DAW (if my understanding is correct).

Unfortunatley, polarity and phase aren't exactly the same thing. The biggest difference is that polarity is simply switching the positive and negative pins around so the wave is going up when it used to be heading downward. Phasing is measured in degrees and can be anywhere between 0 and 360 degrees.

So let's say that you have two microphones (one on a different cabinet being driven from the same amp). For our purposes here we'll assume that all the speakers are in phase with themselves. They may not be. These two mics, if not positioned mega mega perfectly will be out of phase anywhere between 0 and 359 degrees. It's also possible to be 100% in phase at one frequency and totally screwed at another frequency (the reason that this whole micing of multiple amps is so hard).

Even worse is the problem with comb filtering. You'll find that your, depending the amount of distance between the two mics where the given frequencies are in phase together (adding 3dB to the signal) and there may be frequences where the signal is 100% cancelled out (reducing infinite dB).

Comb filtering usually sounds extremely nasally and weird. It takes any fidelity you thought you had and tosses it out the window.

So how do you fix phasing?
The easiest way to fix phasing is to simply use less microphones. One mic is always in phase with itself. Another trick is to move the second mic to be at least 3 times the distance from the source as the first mic. I very very rarely do this.

If you must use 2 or more mics, mic placement is mega mega critical. You will have problems with this at first. Even if one mic sounds great, it may not combine well with the other mic. Spend a few hours, if necessary, to make sure these line up properly. If one mic is 2" away from the source and the second mic is 3" away from the source, you will have problems.

There is a new gadget out called Little Labs IBP. It's a requirement for any person recording with multiple mics to use it. It gives you continously variable control of the phasing. So if the phasing is just 9 degrees off, you can still align it up. Because you can physically twist the knob, you can get a clear idea of what is happening and find the ideal spot.

Brandon

[spec55]

Thanks Brandon...now is see what you're talking about. I just thought it was a polarity problem. The phase issue has every thing to do with the distance the two mikes are from the source. This recording stuff can sure get deep into the physics of sound can't it? I'll have to check out that devise you mentioned or maybe just track one amp after another like your mentioned in a previous thread. Thanks for this gem of an eye opener.

[brandondrury]

maybe just track one amp after another like your mentioned in a previous thread

Well, it's important to note that I wouldn't do this on a Zeppellin type of band. The layering works very well for the modern aggressive rock sounds, but the more layers you do, the more "chorusy" it'll sound. Generally, the 70s rocker typers are highly against layering.

So just keep that in mind.

Personally, I've never had any luck with using multiple amps at the same time. #1 is the phasing issue, but #2 is I never know how to set each amp. I can set one amp to get what I'm looking for. It's not easy, but it's not impossible. However, when you have two amps, how do you set them? Do you set them both to sound great on their own? Do you set one thin and one a little bottom heavy? It ends up opening a pandora's box and so far I've not been able to make it work for me.

When I was down at Wagener's, he had IBPs on every channel. He used 3 amps and 2 DIs and blended them all together on his console feeding a single track into his recorder. It worked well for him, but he had tremendous isolation between his amps and his control room. I think the isolation is the hardest part since most home studios don't have this.

[brandondrury]

This recording stuff can sure get deep into the physics of sound can't it?

It can go as far down as you want to take it, but I've found that this is not the way great music is made and it is not how great sounds are captured. It's my nature to be a math type of guy. I'm into science and rank 0 on the spirituality meter. It's just my nature. Well, most of that has to be tossed out the window. The people getting great sounds usually aren't getting out the ruler. They are listening. If it sounds cool, they do it and if doesn't sound cool, they try something else.

I've had much better luck with just jumping in and twisting knobs that I have with messing with physics. I do understand the physics side just enough to make me dangerous, but my focus is on the music. I'm usually producing while I'm engineering so the last thing I need is to be bogged down by scientific issues when I'm jumping around the control room trying to get a singer or guitar player excited.

Brandon

[Andrew07]

http://www.voxengo.com/doc/pha979/

[brandondrury]

HOLY HELL A SAURUS!!!

You mean to tell me that with all the bitching and whining I've done in regard to phase stuff, no one ever once told me there was a $40 tool that would take care of all of this????

You guys have been holding out on me so you can out-record me. I get it!

Well, it is much appreciated, Andrew07 for you having the balls to come forth even though there is obviously a secret conspiracy out to get me.

To anyone who isn't as experienced with this phase topic, if this plugin works the way it should, it is the single most powerful plugin ever. In fact, I'm blown away that it is only $40.

I'm testing it today!

Brandon

[Andrew07]

if you liked that you'll love this...it's FREE

http://www.tritonedigital.com/produc...products_id=33

I actually can't use the Voxengo stuff 'cause of the whole PC only thing...Let me know how it works out for you dude. Their Tape bus plug is supposed to be pretty cool too

[brandondrury]

Cool. I'll let you know how these turn out.

Brandon