Acoustic recording: multiple mics, phase issues, basic techniques

Crowder

Dang Twangler
Messages
19,078
I'm planning to do an acoustic-centered project in 2017 so I've been experimenting with the mics, pres and spaces that I have to choose from here at home. It'd be great to have some advice from the crew here before I get going in earnest.

I have mics that sound good alone on the guitar, but I'd like to have stereo tracks for the acoustic on this project. I'm having issues combining two mics. I'll get a take where either mic solo'd sounds pretty good, but the two combined are brighter and thinner-sounding than I'd expect.

I suspected phase, but a straight-up phase reversal plug-in didn't seem to correct the tracks (they went to mono mud). Maybe the mics are less than exactly out of phase. Not sure how to correct that.

Thanks,
Mike
 

pbmw

Member
Messages
6,619
I think you're dealing with mic placement issues. Sound is not arriving at each mic at the same time.
There is a rule that I can not think of the name right no, that talks about distance between mics and distance from source. There's a ratio. Rule of threes? Rule of nines?
 

335guy

Member
Messages
5,232
The last time I used two mics on an acoustic guitar while recording, I used a small diaphragm condenser aimed at the 12th fret about a foot away, and a large diaphragm condenser positioned also about a foot away but more toward the lower bout. The guitar was a 000 Martin knock off. Of course, each mic went to it's own channel. I didn't have any phase issues. When I was mixing, I panned the 2 channels fairly aggressively, and eq'ed and comped each channel separately, according to what sounded good to me. Without hearing the track(s) you recorded, it's hard to say why the two mics sound bad, when the individual mics sound good ( although it does seem like it could be a phase cancellation issue ).

Another way I've recorded an acoustic in "stereo" was to double track. This sounds much different than using two mics at the same time though.
 

Rex Anderson

Member
Messages
5,066
It's the 3 to 1 rule, but it won't work for micing an acoustic guitar. http://www.homestudiocorner.com/the-31-rule/

Use an X/Y technique-put the mic capsules one on top of the other (so they are coincident, i.e. no time of arrival differences) and spread them about 90 degrees or so = crossed cardioids.

Aim at the bridge and the 12th fret (ballpark).

You should have perfect mono compatibility so you can pan them however you want.

I never had issues using ORTF or NOS techniques either (slightly spaced).

Are you sure you don't have a mic cable or mic wired out of phase?
 

Crowder

Dang Twangler
Messages
19,078
Thanks guys. Based on the capabilities of the mics I have on hand, I've been playing around with a mid/side setup today. I'm using an Elation KM201 for the mid and an AEA N22 for the sides. I'm digging it so far, though time will tell as I experiment with different rooms and adding other stuff to the mix.

I also have a couple of low-end matched SDC's and will play with the XY and spaced pair approaches to compare.
 

JCM 800

Member
Messages
6,616
I'm guessing there is something else up if you are experiencing such drastic phase issues with two mics on an acoustic guitar.
 

tribedescribe

Member
Messages
621
3:1 as others have said. I have experimented a lot stereo combinations and my favorite combo is a SDC 8-12" from the 14th fret and a LDC pointed at the bridge 3' away. This set up gives you a lot of options to blend in the fullness of LDC and the percussive nature of the SDC. Be careful with your acoustic space as hard surfaces color the mic's in negative ways. Best to experiment with some tried and true stereo techniques on the acoustic and pick one you like.
 

stevel

Member
Messages
14,662
I'm planning to do an acoustic-centered project in 2017 so I've been experimenting with the mics, pres and spaces that I have to choose from here at home. It'd be great to have some advice from the crew here before I get going in earnest.

I have mics that sound good alone on the guitar, but I'd like to have stereo tracks for the acoustic on this project. I'm having issues combining two mics. I'll get a take where either mic solo'd sounds pretty good, but the two combined are brighter and thinner-sounding than I'd expect.

I suspected phase, but a straight-up phase reversal plug-in didn't seem to correct the tracks (they went to mono mud). Maybe the mics are less than exactly out of phase. Not sure how to correct that.

Thanks,
Mike

Mike, I'm not sure why you used the phase reversal plug in. Just center the two tracks and you're monitoring in mono. If you pan them wide and the problem goes away, it's a phase issue. If your interface or DAW has a mono monitor button, you can leave the tracks panned wide, press this, and it basically centers them - again, if the problem is there in mono (centered) but not there panned, you've got a phase issue.

If you're going to pan them wide, it doesn't really *have* to be mono compatible- but as pointed out above, the point of X/Y setups are to eliminate the arrival time difference (negating phase issues) meaning you can pan them both center, or spread wide, or anywhere in the spectrum you want.

X/Y may not give you as big a "spread" as you want as the left and right image is then based on INTENSITY at the arrival point rather than arrival time. So if your signal isn't really all that different from both sides, you may not get the effect you want.

"Dual mic'ing" is slightly different from stereo mic'ing in that you're really getting two more different that more similar signals but there's nothing wrong with it - it's just as you put more distance between the mics, the 3:1 rule does come into play.

You should learn how to take a mono guitar track, send it to a stereo reverb, and return the reverb in stereo. This is the classic way for mono tracks to appear in the stereo spectrum (especially when planning to add reverb in the final mix as everyone does nowadays).

This sort of accomplishes what mid-side does - where you get a "dry" center signal on the mono track, then "wet" stereo reverb returning to the main stereo bus (or a stereo channel which also allows you to adjust width and balance).

It has a more realistic sound if that's what you're after.

But again of course, multi-micing is commonplace as well and it generally means a lot of experimentation with placement.

If you have any more mics, it would be wise to go ahead and record as many mono tracks of the guitar that you can - do a stereo pair and some singles, or do a bunch of singles, or mono-compatible singles, etc. so that when it comes to the mixing stage, you'll have more tracks of signal to combine and experiment with - just in case a stereo version doesn't sit right in the mix and you have to choose 2 single mono ("dual mono") tracks for a stereo image, or the stereo reverb return for stereo, or even 3 tracks, etc. The more you have recorded the more options you'll have. Better than having to re-record!
 

Crowder

Dang Twangler
Messages
19,078
Thanks all. I started messing with mid/side today since a couple of my best mics are an sdc and a figure 8 ribbon. I was liking what I heard with minimal processing. I was curious whether mid/side would be hard to mix so I cut a scratch vocal and bg vocal. I think the acoustic sounds reasonably good.

 

ronzie

Member
Messages
486
It's the 3 to 1 rule, but it won't work for micing an acoustic guitar.
Rex named what pbmw couldn't remember and is not endorsing the rule in this instance. And Rex is correct that it doesn't apply to Crowder's situation. It's a single sound source.

The three to one rule applies to dual sound sources.
Two differing sound sources. Not to two transducers on one sound event.

This is(mostly)correct. The portion in "red" is the rule and spot on... Just don't look at the awesome graphic representations. LOL.

3:1 as others have said.
That's not what Rex was saying....

The 3:1 rule is for leakage from one source to another, not phase between two transducers from one sound source, which is more in the heading
of inverse square and/or power law.

Picture Crowder with 2 mics. One for his acoustic and one for his vocals. He sings and plays as one event. This is where you apply the 3:1 rule. Keeping the leakage to manageable degree from the guitar into the vocal mic and the vocal into the guitar mic.

The only thing going on here, is Crowder needing stereo recording with an aesthetic he likes, while the technical integrity holds together.
 

tribedescribe

Member
Messages
621
When did crowder say he was cutting vocals at the same time, did I miss something?

I get the 3:1 rule mixed up with phase so you may be right about it.
 

loudboy

Member
Messages
27,335
Here's a raw track I did in the artist's living room.

Spaced pair, Mic 1 is about 12-14" off the neck, pointed at the neck/body joint. Mic 2 is about 10" off the lower bout, pointed little behind the bridge.

Signal chain: Huss & Dalton Guitar > KM-184 Pair > Great River MP-2MH > Mytek ADC 192.

Not really any phase issues, and if panned hard, like in the sample, the guitar is huge. At mixtime I brought it in to about 10 and 2, as I didn't really want the "6-foot wide guitar" for this song.

 

ronzie

Member
Messages
486
When did crowder say he was cutting vocals at the same time, did I miss something?

I get the 3:1 rule mixed up with phase so you may be right about it.
I should have been more clear. It was a simple example of when one would use the 3:1 Vs. what Crowder was actually doing.
 

Crowder

Dang Twangler
Messages
19,078
Here's a raw track I did in the artist's living room.

Spaced pair, Mic 1 is about 12-14" off the neck, pointed at the neck/body joint. Mic 2 is about 10" off the lower bout, pointed little behind the bridge.

Signal chain: Huss & Dalton Guitar > KM-184 Pair > Great River MP-2MH > Mytek ADC 192.

Not really any phase issues, and if panned hard, like in the sample, the guitar is huge. At mixtime I brought it in to about 10 and 2, as I didn't really want the "6-foot wide guitar" for this song.

Cool. I hear what you're saying about making the sound fit the song. That's one of the reasons I find mid/side appealing for this. Worst case, you have a good single source sound captured, but you also have the option of making the guitar much wider. You can even pan the "mid" a bit and it doesn't break down.
 

rockabilly69

Silver Supporting Member
Messages
1,905
I agree with the M/S technique and recording acoustic guitars is my main thing! I find that having the option of the side mics at mixdown is
great for many things, depth, tonal control, etc. A very good reasonable priced combo for recording acoustic guitars in MS is a RODE K2 and
NTK combo, into a dark preamp (my favorite is the Drawmer 1960). I've gotten many good recording with this setup. Here's the NTK/K2
combo straight into my RME Babyface preamps, I also added a send from the magnetic pickup.

 

Crowder

Dang Twangler
Messages
19,078
I agree with the M/S technique and recording acoustic guitars is my main thing! I find that having the option of the side mics at mixdown is
great for many things, depth, tonal control, etc. A very good reasonable priced combo for recording acoustic guitars in MS is a RODE K2 and
NTK combo, into a dark preamp (my favorite is the Drawmer 1960). I've gotten many good recording with this setup. Here's the NTK/K2
combo straight into my RME Babyface preamps, I also added a send from the magnetic pickup.

Nice stuff
 




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