Do you Invert Polarity in recording of guitar?

[AcousticDreams]

Been reading lots of articles about the difference between Phase and Polarity. A bit confusing, however I am starting to understands the real differences.

I have witnessed Doug Young using a easy to use Phase alignment plug in. Seems like this would be a great addition. And I also saw a demo on PI, that can after the fact align the two signals?

But how many of you Invert Polarity when using just two microphones? What microphone techniques have you used where you find this a valuable function? I guess the real question is just how important is the Polarity switch for the recording of guitars? In recording of a snare(Top & Bottom) and the two mics face each other, it has been noted that the polarity switch is of great value. But is there a need for Acoustic guitar? Do mics ever face each other with Acoustic guitar? Or are there other acoustic guitar recording scenarios where polarity might make a difference?

[Doug Young]

Originally Posted by Knives&Guitars

Been reading lots of articles about the difference between Phase and Polarity. A bit confusing, however I am starting to understands the real differences.

I have witnessed Doug Young using a easy to use Phase alignment plug in. Seems like this would be a great addition. And I also saw a demo on PI, that can after the fact align the two signals?

But how many of you Invert Polarity when using just two microphones? What microphone techniques have you used where you find this a valuable function? I guess the real question is just how important is the Polarity switch for the recording of guitars? In recording of a snare(Top & Bottom) and the two mics face each other, it has been noted that the polarity switch is of great value. But is there a need for Acoustic guitar? Do mics ever face each other with Acoustic guitar? Or are there other acoustic guitar recording scenarios where polarity might make a difference?

The phase alignment tool I have is useful when using multiple pairs of mics, I wouldn't use it with just 2. it was actually created for use with drums, where multi-mic setups cause lots of issues. Also, I've found it to be more useful as a learning tool. When I first got it, I was getting dramatic results - big corrections. Based on the info it gave me, I was able to improve my multi-mic placement, to where it isn't as useful, not needed, I tend to get the mic pairs in good phase correlation to start with.

I would never use a polarity switch with an acoustic guitar recording with any of the micing techniques I use, unless one of the mics, or cables was mis-wired. (an exception is doing MS manually with 3 channels during mix down) Phase is best adjusted by mic placement. XY and MS will be as perfectly in phase as you can get. ORFT-like placement will have some phase differences, and spaced pairs may have a lot - those are features, not a bug, it's how those placements produce a stereo sound. As long as your mics are reasonably close to the same distance from the guitar, you shouldn't have to do anything about phase. If you start using multiple pairs, room overheads, or something to augment your close micing, you may want to do something - or not. I've been mixing some stuff recorded with a cello using a single close mic and a pair of distant room mics. Clearly there will be some phase differences between these, but I don't hear or observe any problem, the room mics just add some "room", which adds a bit of space.

[rick-slo]

Don't switch polarity - unless you somehow recorded accidently with polarity switch and you are switching it back.

[Bob Womack]

I'll bite. I'm a recording engineer/producer. Phase and polarity are two things I keep close track of. However, doing sessions, I don't have a lot of time to muck about with arrays that would introduce phase or polarity issues into my recordings, so I have developed some rather precise arrays that I can use that give me predictable and reliable results. I've even come up with a snare array that gives me my sound without a polarity change. It involves a cardioid pointed down at the top head and another pointed at the side of the snare at 90' that I move vertically until I get the right snare sound. Why? Besides simply doing music, I also do music concert videos and broadcast. When you record, you don't know if you'll be doing the mix. If you know you'll be doing the mix, you may not know until the last minute who is doing the record. Having an easily-reproducible array you can use or send a sketch of to the recordist to get a predictable result is very useful.

I work with a DK surround meter and iZotope Insight (which has a similar meter) that allow me to see the relative phase coherence of two signals. In stereo, a single vertical line shows absolute phase coherence. A single horizontal line shows absolute phase incoherence. In between is a field that shows the relative coherence state of a stereo signal or soloed pair.



Bob

[AcousticDreams]

Originally Posted by Doug Young

Phase is best adjusted by mic placement. XY and MS will be as perfectly in phase as you can get. ORFT-like placement will have some phase differences, and spaced pairs may have a lot - those are features, not a bug, it's how those placements produce a stereo sound. As long as your mics are reasonably close to the same distance from the guitar, you shouldn't have to do anything about phase.

Originally Posted by Bob Womack

I've even come up with a snare array that gives me my sound without a polarity change. It involves a cardioid pointed down at the top head and another pointed at the side of the snare at 90' that I move vertically until I get the right snare sound.
Bob

When I got my new pair of Schoeps CMC621's, a few days ago, I experimented with a few techniques.

The Best result was something nearly similar to yours Bob, with a close miced space pair at 90 degrees. I am very happy with the results. Exactly what I had hoped for. I was so relieved that what I thought in theory might work, actually in fact did work. Especially since I had never used the 21 capsules before.

As a designer of sorts, often what works on paper, does not work in the field. Once I designed a leather archery hunting quiver that was quite cleaver in theory. When I got it into the field, it proved to be only a marginal design and certainly not up to my standards. And years ago while on a Canadian outback canoe trip, one of my canoe companions bought a new water filter. He did not use it before going out. He was greatly disappointed. He said " I wonder if the engineers ever get out into the field and actually test their own products" the angle of the pump made it hard to use.

But if it were not for my failures in designs and physical methods, I would have not come up with what are often considered a unique designs and methods. Plus as I always say, experimentation is fun. I might like experimentation as much as I do playing.

And if it were not for my questions...well let us just say, that I tend to fuss over the little stuff sometimes. Way too much! And with Great Answers Doug about Phase issues not being much of an issue with a proper two mic set up...it is one less thing to me to worry about. (One of the products I am considering does not have an external polarity switch..only internal)

Well, I am one step further to ordering my next piece of gear.
For the most part, Most of my conclusions on what gear I will be needing is almost exactly the same as what I thought a year and a half ago. But I can not tell you just how appreciative I am to all of the answers provided. These are large investments for myself and the answers I have received have help me in all kinds of ways. Sometimes the Answer of one question confirms a doubt or confirmation in another area.

There are no absolutes. What often we think will work, just does not. What we think we need...if often not what we really need. But it sure feels good when it does work out.

[Brent Hahn]

Many modern tube mics, U47 clones and such, come with generic third-party power supplies. These supplies quite often flip polarity at some point between the input from the mic and the XLR output. This is strange, since that's just supposed to be a straight wire from Points A to B, but there you go.

So if you're recording a singing guitarist and finding that the sound of the two mics together is beefier if you flip polarity on one of them, there's a good chance that that's why. If you can solder it's an easy DIY fix, but the manufacturer should really fix it for free.

[Doug Young]

I had a "matched pair" of mics once where 1 was flipped in polarity :-) So it happens. I doubt you'll have that issue with the Schoeps

[AcousticDreams]

Originally Posted by Brent Hahn

Many modern tube mics, U47 clones and such, come with generic third-party power supplies. These supplies quite often flip polarity at some point between the input from the mic and the XLR output. This is strange, since that's just supposed to be a straight wire from Points A to B, but there you go.

So if you're recording a singing guitarist and finding that the sound of the two mics together is beefier if you flip polarity on one of them, there's a good chance that that's why. If you can solder it's an easy DIY fix, but the manufacturer should really fix it for free.

Actually Brent, this has been another question on my mind= 48 volt phantom power supplies.

I believe in the old days...you always had to buy a separate phantom power supply....and they were not cheap. In my old U87, it luckily had the option to go with an internal batteries, or switch over to dedicated Phantom power supply. I always ran mine on battery as I did not have a phantom power supply because of the added expense.

If I remember correctly, the old dedicated Phantom power supplies were not that small either. And they cost quite a bit as well. However, maybe just like the difference in expense of a 500 series and rack unit...a lot of the cost is in the metal box?

What I have been told by one company is that the quality Power supplies in 500 series racks do make a difference. That some units are better than others.

So this leads me back to a new question about 48volt phantom power supplies in interfaces.

Could not the quality of a Phantom Power supply effect some sort of sound difference in a mic? Effecting the efficiency and or enabling for the microphone to work at its full potential? Or is it purely about hum and noise?

[Brent Hahn]

The only interface with a mic input I've ever had (and still have) is an Apogee, and it only powers one mic. Never had a problem there, but I'm not really qualified to speak on the subject. I've got a standalone 2-channel supply that I bought to supply phantom to the "instrument" input of the Apogee. A 2" cube, more or less, cost me $50.

[Bob Womack]

I started my career on Neve consoles, 8032s and 8024s. Here is one I spent years on:



They had no phantom power. Back then there were three standards so you bought your console and then your facility settled on a standard and bought power supplies. We settled on Phantom and had individual boxes. The AKG N46e two channel power supply I used back then. It was 5" tall by 3" wide by 6" long. It looks like the one on the left below. The two on the right are T-power supplies, one of the other of the three standards. I think we have a couple of old Sennheiser MKH416 T shotguns that use this standard and haven't been converted.



Technically, the spec for phantom included absolute audio transparency. If you notice the high pass filters on the N46e: I am told that this supply is also transformer-coupled, so it isn't purely a phantom power supply. HERE is one on Reverb. They typically still fetch around $200. Modern supplies are far cheaper.

Bob

[jim1960]

Sound Radix makes a plugin called Auto-Align that is simple to use and does an excellent job of aligning phase. Give it a trial run on double-mic'd guitars. It's a pretty impressive bit of kit.

[rick-slo]

Originally Posted by jim1960

Sound Radix makes a plugin called Auto-Align that is simple to use and does an excellent job of aligning phase. Give it a trial run on double-mic'd guitars. It's a pretty impressive bit of kit.

The issue with this the "best" overall phase alignment of right and left stereo tracks does not necessarily give the best sound though it could be a reasonable starting point. A stereo track could be wildly out of phase yet be great sounding.

[Doug Young]

Originally Posted by jim1960

Sound Radix makes a plugin called Auto-Align that is simple to use and does an excellent job of aligning phase. Give it a trial run on double-mic'd guitars. It's a pretty impressive bit of kit.

Yes, that's what I use. I wouldn't use it on stereo mics tho, it would totally destroy the intended relationship. Can be useful when using more than 1 pair, or when combining a pickup and mics. As mentioned, it seems to have been developed originally for drums, where using lots of mics gets complicated due to the bleed being out of phase.

[AcousticDreams]

Originally Posted by Bob Womack

I

Technically, the spec for phantom included absolute audio transparency. If you notice the high pass filters on the N46e: I am told that this supply is also transformer-coupled, so it isn't purely a phantom power supply.
Bob

*Do you believe that the individual higher quality Phantom power supplies gives better Audio Transparency? Are the newer-cheaper phantom powers as good as the old?
* And what role did the Transformer coupled Phantom power play in the recording chain? Was the transformer there for transformerless boards?

Originally Posted by Doug Young

Yes, that's what I use. I wouldn't use it on stereo mics tho, it would totally destroy the intended relationship. Can be useful when using more than 1 pair, or when combining a pickup and mics. As mentioned, it seems to have been developed originally for drums, where using lots of mics gets complicated due to the bleed being out of phase.

Just to clarify, are you saying that for two separate mics do not need phase alignment tool?(I think that is what you are saying) Or are you saying for a single Stereo mic?

[Doug Young]

Originally Posted by Knives&Guitars

Just to clarify, are you saying that for two separate mics do not need phase alignment tool?(I think that is what you are saying) Or are you saying for a single Stereo mic?

Separate mics. Well, either, I guess. A stereo mic's going to be very much in phase already. But I mean with 2 mics, like you're using. With 2 mics, I would not play games with processing to change the phase (unless you were trying to rescue someone's bad recording, or want some unusual effect). You choose your mic placement according to the sound you want. Co-incident setups like XY should not have any significant phase differences anyway. For spaced pairs, phase differences are part of what makes the stereo sound, so you wouldn't want to alter that (I wouldn't anyway). If you think you have too much phase differences in a spaced pair recording, I'd move the mics, maybe closer together, less spaced out. Basically just use mic placement to get the sound you want.

Of course, recording's an art, so if you get a sound you like by doing something unusual, that's OK, but I'd start by getting fairly standard mic placements working for you, there are a half dozen or so that people use, and they all work, and each has a certain "sound". Once you get those down, you can play any games in the mix you want, you might find something you like.