What do you all like for mics on an acoustic guitar?

[PorterhouseMusic]

That always just caused huge phase cancellation for me...

I think M/S is a cool technique that can yield good results. But It has a couple of inherent things about it that are to be considered. I don't claim to be an expert - but I've deliberately spent a lot of time testing with it for the sole purpose of trying to understand it better and how best to utilize it. Fortunately - there's quite a bit of information out there - but not all of the videos and explanations cover the idiosyncrasies.

A couple of points:

There is an inherent phase cancellation (to one side of the stereo field) built into it. This is probably what you're referring to. It's more a matter of managing this than getting around it- as it's just the way it works.

Because of that partial phase cancelation on one side of the stereo field there is an inherent signal imbalance once all the information gets to the stereo bus. **This drove me nuts at first years ago - until I started to understand it and compensate for it.

The other thing I have discovered - is that not only is there a slight imbalance naturally from this technique - but how the source is positioned relative to the microphones makes a difference. In addition to that - I learned that mic placement relative to room acoustics is also a factor. If the side mic (set to fig 8) is picking up reflections on one side and not the other - this can throw off balance as well.

So - it seems - there's a lot going on there to use this technique, get things right, and have it be effective and useful. That's been my experience anyway.

Would love to hear from others who have spent time with this.


This video is one of the better ones in terms of explaining the technical aspect of the technique and the phase cancellation bit:

 

[DrewPeterson7]

I'll give this a look later when I have a little more time - I haven't experimented extensively with the technique, but what experimentation I have done yielded a very "hollow" sound where phase cancellation changed widely depending on where in the listening space I was, which made it basically unusable. I assumed this was because your side takes sum to null, and I'm not sure I see a way around that... I mostly record stereo acoustics as single takes L and R, but even if this isn'y something I end up using much, it's certainly a technique worth knowing... And, that whatveer was causing my issues, was probably user error. :lol:

 

[Steenamaroo]

There is an inherent phase cancellation (to one side of the stereo field) built into it. This is probably what you're referring to. It's more a matter of managing this than getting around it- as it's just the way it works.

Because of that partial phase cancelation on one side of the stereo field there is an inherent signal imbalance once all the information gets to the stereo bus. **This drove me nuts at first years ago - until I started to understand it and compensate for it.

The other thing I have discovered - is that not only is there a slight imbalance naturally from this technique - but how the source is positioned relative to the microphones makes a difference.

There's no phase cancellation with mid/side, and no inherent signal imbalance unless the physical construction of the fig-8 mic is not symmetrical.

That's kind of the point of the setup - The physical position of the microphone makes meaningful phase cancellation impossible,
and the fact that stereo imaging is derived from the movement of one single capsule makes imbalance impossible, physical a-symmetry set aside.

If you're referring to one copy of your figure 8 signal having inverted polarity, that's not some weakness or flaw which needs to be worked around.
That's, mathematically, how the setup works.

Both microphones 'agreeing' (outputs moving positive/negative in tandem) comes from a sound source somewhere on the left side of the setup.
Therefore, both microphones disagreeing (outputs moving positive/negative against each other) comes from a sound source somewhere on the right.

Mid side is, essentially, a calculation that says 'when these mics agree play it out the left, and when they disagree play it out the right',
but further to that it actively cancels right output from left sound sources, and vice versa.

That's partly why it can sound much wider and more hollow than traditional two-mic setups.
A three cardioid equivalent would be purely (almost) additive and wouldn't suffer from the unnaturally wide possibility.

For that reason it's generally better to use mid/side from a distance, or go easy with the panning.

 

[PorterhouseMusic]

Omg - I'm so confused. And clearly missing some fundamentals here. And just when I thought I was starting to understand this. And why I - and so many others - get an imbalance on the stereo bus when the tracks are combined - but not before.

Thanks for your comments. I'm determined to wrap my head around this and get to a full understanding.

Out the door for work - but I'll get back to this asap. Thanks again

 

[Steenamaroo]

The image being so extreme, especially when working close to an instrument, is likely to present as an imbalance.
Really it's more of an exaggeration of what's real - There is an imbalance (or lack of symmetry) with an acoustic guitar or piano, for example,
and mid/side shines the biggest possible light on that.

That's why mid side is so often used for ensembles - A room technique rather than spot instrument.

Can still be very usable up close, though, if panning isn't extreme and/or volume of sides is reduced,
but note that any small movement by the performer and instrument can still be quite pronounced.

Worth experimenting with, for sure.

 

[R D Smith]

I watched the Audio University mid-side video and several others on their channel. I thought they were very informative and made to concepts easy to understand. Thanks for posting it PM.

 

[DrewPeterson7]

The image being so extreme, especially when working close to an instrument, is likely to present as an imbalance.

Come to think of it, in a recent thread around here where I mentioned trying it and not having much success, I do think I remember someone mentioned it wasn't really a suitable approach for anything akin to a "close mic'd" instrument, and if the mic pair were within several feet of the source it was likely to cause problems. I haven't gone back to test and see if this was my problem, but when I get the time I should.

 

[Steenamaroo]

I think I found it.
Guess who...

 

[PorterhouseMusic]

I think I found it.
Guess who...

It was good to review that. Thanks. The distinction between "phase" cancellation and "reverse polarity" is an important one when talking about this. It makes sense that phase cancelation is frequency dependent. As opposed to cancelation as a result of reversing polarity - which is total across all frequencies.

Not sure when I'll have the proper time to come back and visit this - but a few random comments on this given where I've come from and where I'm at.

Many years ago when I first learned about m/s - I setup in the house where I was at and simply recorded my acoustic gtr without having read anything about the how's and why's of m/s decoding. As I recall - my recording turned out beautifully. It was as spacious as I wanted - and *balanced*.

After moving to my new house where I have a more suitable dedicated recording area - the m/s recording I've done here has been more hit and miss. Mainly having to do with balance issues in the stereo field. Like bad imbalances. But it seemed worse with different setups and locations in the room. Or so I thought.

I have three different mics that all have fig 8 capability. I still have balance issues with all three *depending* on how I set this up. It seems..... that position in the room and position relative to the mic(s) play a considerable role.

Why I thought and spoke about cancelation being inherent is because of this. Of course I did , in error, refer to this as "phase" cancelation. I now know that it is not phase cancelation.:



And if you look around you'll see that many people report balance issues when recording acoustic gtr with m/s technique. Even looking at the stereo meters on some of the videos out there - you can SEE this.

At the end of the day - I'm just curious. Why, specifically, does this happen? What is the cause? Thought I was getting a handle on this - but I'm checking myself now.

 

[Steenamaroo]

It's probably just an accurate, albeit extreme, representation of what's happening in the room,
rather than an issue or problem.
We know sound doesn't emanate symmetrically from a guitar - If you have a close spaced pair, it's very obvious that one is rich and bassy,
and the other is thin and brighter.

Without hearing your clips I'd bet that's all it is. Perhaps your new room exacerbates that,
maybe you're sightly closer than with previous recordings... Could be a few things.

If the imbalance is consistent and pronounced you should be able to move a little to compensate.
If it's inconsistent then you're probably hearing the result of moving slightly while you play.

If you increase distance a bit the setup becomes slightly more forgiving and more consistent.