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Acoustic guitar recording multiple mic query

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Acoustic guitar recording multiple mic query

Postby rggillespie » Fri Jul 31, 2020 4:14 pm

I’m recording my acoustics with a cardioid condenser at the 12 fret and Reslo ribbon aimed down at the bottom of the body. They are both about 8 inches away from the guitar and about 20-24 inches apart. I’m aware of possible phase issues and have just read tapeop magazine where a producer uses something called sound radix auto align. It seems to be a plugin that sorts out phase issues, I was wondering if anyone had heard of this type of plugin and had used it? I feel that sometimes my recordings are tight and focused and then the next time they can feel disjointed. I’ve assumed it’s a phase /comb filtering issue as I can’t get the mics exactly as they had been before? I find the two mic approach sounds more like how I think the guitars actually sound so I’m reluctant to go back to using a single mic approach. Any thoughts much appreciated as ever
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Re: Acoustic guitar recording multiple mic query

Postby Hugh Robjohns » Fri Jul 31, 2020 5:19 pm

There are a few plugins that can auto-align similar waveforms. I've not used Radix myself, but I've heard of it being used.

Bear in mind that the phase relationships will inherently change if you move the guitar as the relative distances between sound source and mics will change, and thus the phase relationships will also change.

Assuming you pan the mics left-right, listening in mono will instantly reveal any problems with the phase relationships, and moving one mic (or re-positioning yourself relative to the mics) will improve things.
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Re: Acoustic guitar recording multiple mic query

Postby rggillespie » Sat Aug 01, 2020 7:40 am

Thanks for the panning mono tip Hugh, it’s tricky replicating the spacing exactly every time so I’ll try this plugin On trial and see if it helps with some recordings I’ve have available. I had thought it may have been not helpful that one mic is cardioid and the other figure of eight. As they are recording different spaces at the same time they would be inherently out of phase. Maybe that’s not relevant though. Perhaps I should try the xy recording technique as an alternative?
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Re: Acoustic guitar recording multiple mic query

Postby CS70 » Sat Aug 01, 2020 1:31 pm

In broad terms, the phase issues are due to the signals being essentially identical, but recorded at slightly different times (the time that it takes from the source to reach the capsule diaphragm) so that when they sum, the interference generate comb filtering at least in certain bands.

If you use a figure-8 with the "front" lobe oriented towards the source, the wave that hits the front of the capsule will be the same as a for the cardioid mic (only slightly delayed). The figure 8 mic will also add the back reflections of course to its output signal (so the signal will be slightly different), and different capsules with drastically different geometry, elasticity and other physical properties will produce even more slightly different waveforms.

However, the bulk of the signal is produced by the same air wave, so even with mixed mics you're likely to have phase problems at least in some bands... the trick as you know is to minimize the comb filtering with position (and trying to stay still when playing :)).

Or my favorite way of recording acoustic guitar - panning two identical takes in mono :)
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Re: Acoustic guitar recording multiple mic query

Postby resistorman » Sun Aug 02, 2020 4:10 am

On the other hand, I stuck one mic in front of my guitar for a demo recording and it sounded so good I used it. I dunno, maybe it was the freedom of just doing a "demo". The playing and sound were just right.
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Re: Acoustic guitar recording multiple mic query

Postby rggillespie » Sun Aug 02, 2020 6:53 am

I’ve not felt I capture all of my acoustics sound fully using just one mic. A mic at the 12 fret captures the harmonics and higher end and the one on the body captures the ooomph. I then mix them to taste, to me that sounds most like what I think I’m hearing. I’m trying to do some songs with just one acoustic and vocal so the recorded guitar is very exposed. So I want to get all of the acoustics sound, not so important if it’s being used on songs with a band of course. That being said I did have excellent results using an akg valve c12vr mic on its own, when I had a chance to use one. I’ll try the identical mono takes idea, download the auto align plug on trial and let you know how it goes, both much cheaper than saving for that akg mic!
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Re: Acoustic guitar recording multiple mic query

Postby adrian_k » Sun Aug 02, 2020 7:18 am

Or just for fun, with those mics you could try recording MS if the fig 8 pattern of the Reslo is symmetrical.
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Re: Acoustic guitar recording multiple mic query

Postby blinddrew » Sun Aug 02, 2020 9:41 am

I've been using M/S a lot on guitar recently. No phase issues and you can decide how wide you want the guitar sound to be in post. You can even vary it in the mix; if your track starts off with a fairly isolated guitar part you can give it a bit of width but then narrow it down to give other instruments space as they come in. You can even play around with extreme settings as a bit of an effect.
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Re: Acoustic guitar recording multiple mic query

Postby CS70 » Sun Aug 02, 2020 10:13 am

rggillespie wrote:I’ve not felt I capture all of my acoustics sound fully using just one mic. A mic at the 12 fret captures the harmonics and higher end and the one on the body captures the ooomph. I then mix them to taste, to me that sounds most like what I think I’m hearing. I’m trying to do some songs with just one acoustic and vocal so the recorded guitar is very exposed. So I want to get all of the acoustics sound, not so important if it’s being used on songs with a band of course. That being said I did have excellent results using an akg valve c12vr mic on its own, when I had a chance to use one. I’ll try the identical mono takes idea, download the auto align plug on trial and let you know how it goes, both much cheaper than saving for that akg mic!

Not questioning at all - everyone's got their approach... but as with resistorman hinted, I go for mono mics (but doubled takes) especially when the acoustic guitar is totally exposed and I want to give that feel of realism, intimacy and nearness.

I guess it's because when you listen to an acoustic guitar in songs performed that way, the guitar is essentially a mono source to you. Sure you can use two mics and then collapse the stereo image but by definition part of the frequencies will overlap, and - even if you avoid phasing - you will have some reinforcement of the common frequencies so the timbre will change. Sure you can EQ it down - but I find it's not worth the hassle. M/S fares better in that regard - because of its well know properties, but still..

On the other side, stereo spreading - at least any spreading that's noticeable - fits songs which require less realism and are more "bigger then life".. Odin surely had a 4 mt wide custom-made Gibson acoustic :D

Of course there are no rules and these are just my opinions, are subject to change anytime if the song demands it! :)
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Re: Acoustic guitar recording multiple mic query

Postby Hugh Robjohns » Sun Aug 02, 2020 10:31 am

rggillespie wrote:I’ve not felt I capture all of my acoustics sound fully using just one mic. A mic at the 12 fret captures the harmonics and higher end and the one on the body captures the ooomph. I then mix them to taste, to me that sounds most like what I think I’m hearing.

Like most large-ish acoustic instruments, the 'complete sound' only forms into an homogenous whole at some distance from the instrument itself -- it's the combination of sounds radiated from the different resonant parts of the instrument body and strings, as well as the mechanical noises and acoustic reflections from the floor. A reasonable rule of thumb is that the sound comes together at a point slightly further away than the longest dimension of the instrument...

However, because most amateurs record in relatively poor-sounding rooms, they generally can't place mics that far away because they get more (nasty) room than instrument... so they are forced to close-mic instead. And as soon as you do that you inherently get an unbalanced sound because the mic only 'hears' a part of the instrument and not the whole sonic picture. So you are inevitably forced into adding additional mics to try and capture all the other elements that the first mic misses out on.

Hence the very common solution of a combination of neck and tail mics in one form or another.
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Re: Acoustic guitar recording multiple mic query

Postby rggillespie » Sun Aug 02, 2020 12:07 pm

Certainly sounds worth me trying ms technique, I like the idea of being able to make the guitar sound intimate, small scale even. Songs like Julia on the white album, early Dylan or Gillian Welch's time revelator album all seem quite small scale and bare. Giving you some sense of being in the room with them. That's roughly what I'm aiming for allowing for the very sizable talent gap! Reading up on the recordings of Gillian Welch they seem to use a mic per guitar and one per voice, plus RCA B studio in Nashville. So best not get too ahead of myself with what I can achieve. I'm set up now to be facing the longest axis of the room to avoid early reflections, the rooms treated but not large. Time for some experimentation then, I'm finding its the hardest thing to record, and when its not right its so clear. I'm trying to get it right at the source and process as little as possible later. I feel the less plugin processing the better, they seem to take away as much as they give. Though that is likely to be the operative...
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Re: Acoustic guitar recording multiple mic query

Postby blinddrew » Sun Aug 02, 2020 12:42 pm

I've found it's taken me a loooong time to get an acoustic guitar sound I was happy with. I went through a variety of twin-mic techniques, then back to one mic, then back and forth again but I'm finally getting some stuff that I'm happy with using M/S - but it is a fairly heavily treated room.
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Re: Acoustic guitar recording multiple mic query

Postby CS70 » Sun Aug 02, 2020 2:49 pm

rggillespie wrote:Certainly sounds worth me trying ms technique, I like the idea of being able to make the guitar sound intimate, small scale even. Songs like Julia on the white album, early Dylan or Gillian Welch's time revelator album all seem quite small scale and bare. Giving you some sense of being in the room with them. That's roughly what I'm aiming for allowing for the very sizable talent gap! Reading up on the recordings of Gillian Welch they seem to use a mic per guitar and one per voice, plus RCA B studio in Nashville. So best not get too ahead of myself with what I can achieve. I'm set up now to be facing the longest axis of the room to avoid early reflections, the rooms treated but not large. Time for some experimentation then, I'm finding its the hardest thing to record, and when its not right its so clear. I'm trying to get it right at the source and process as little as possible later. I feel the less plugin processing the better, they seem to take away as much as they give. Though that is likely to be the operative...

A large room may truly do wonders to an acoustic guitar sound. One of my previous flats was a converted loft where the living room was very large and had 4.5 meters roof, sloping walls, wooden floors and a one of the walls made of bricks.. best place I've seen to record acoustic guitar outside a local large studio.

Since recording guitars doesn't require that much gear and gear setup, if you find some large space available for an afternoon, it's definitely worth getting the gear there and try. You may be surprised how much the size of the space does. Also count spending at last half an hour testing positions!

As of processing... dunno. Lots of people seem to have that idea, but I can't see really the logic. I mean, doing less work: yes! Getting the best possible source: yes!

But as of post-processing.. when you record anything you're already going thru several stages of changing the sound from what you perceive directly. It goes thru the mic, the preamp and ultimately the playback system (and as we know they're all different). You place mics nowhere near where your ears are. Even more importantly, the way sound is processed by your brain when you're in the room is quite different than when you're listening to a recording. Stuff that you may not even notice when listening live (like ambient noise) can make a recording unusable. The room "equalizes" the sound in lots of ways, good and bad. And so on..

The whole "don't want to process much" thing feels (to me) like a bit artificial and constructed - like there was somewhat any moral merit in "not processing". There isn't. :D

Imho the goal is the sound that's in your head. If you have to process one minute or one week to get it, so be it. Who cares? I want people to hear a sound and go "wow!" at the best of my abilities (which are, of course, unfortunately scarce :D).

Obviously the utmost care should be placed in every stage of the process - beginning with performance, room selection, mic placement, performer placement, mic selection, recording etc.. but once I've got a great take, I will put zero limits to what I do with it to make it sound astounding. They're all means to an end - getting the sound of the mix that you have in your head. It's hard stuff to learn (and one never stops), but definitely worth it.

My $.10 of course, and I can surely be wrong.. :D
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Re: Acoustic guitar recording multiple mic query

Postby adrian_k » Sun Aug 02, 2020 3:59 pm

CS70 wrote:You place mics nowhere near where your ears are.
This, twenty times over. Mind you I sometimes put a mic over the player’s shoulder from behind. But yes, in general and for those of us recording in less than perfect spaces there can be a lot of work to get the guitar to sound how it does in your head.

I worked with someone who wasn’t getting the results he wanted at quite a famous studio. We tried various micing positions at my place but nothing hit the spot for him. In the end I got there but after literally days of trying different approaches in post processing.
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Re: Acoustic guitar recording multiple mic query

Postby rggillespie » Mon Aug 03, 2020 8:00 am

Thanks for the detailed replies, I always appreciate the help and guidance offered. Of the things I record I realise the acoustic is only one, in a sense, I've never heard properly in the room because I'm playing it. I don't know how it sounds from 6 foot away facing it in the room. So my perception of the definitive sound is probably based more on records etc than actually the sound I'm producing in the room. Anyway I've read up and I'm all set for for some ms recording after work, looking forward to seeing how it goes. I take your point CS70 about processing, I need a better grasp of what any plugin is doing to make it work to my advantage. Still quite some way to go understanding the technical side of of eq, compression, side chains, stems, reverb etc. Getting there bit by bit and enjoying the ride, so it's all good.
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