HOW TO MIC’ GUITAR AMPS IN THE STUDIO

Started by Elantric, October 20, 2014, 12:50:02 PM

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Elantric

http://www.audiotechnology.com.au/wp/index.php/how-to-mic-guitar-amps-in-the-studio/
HOW TO MIC' GUITAR AMPS IN THE STUDIO
Published On March 25, 2014 | Tutorials
Mark Opitz's guitar amplifier microphone technique.
Having worked with bands like INXS, AC/DC, Cold Chisel and the Divinyls, Mark Opitz, suffice it to say, knows a thing or two about recording guitar amps. AudioTechnology caught up with Mark at Studios 301 in Sydney where he revealed one of his prized techniques for capturing the amplified guitar sounds. Rather than be secretive about the way he works, keeping the best tricks up his sleeve, Mark is happy to share his engineering experience. What follows cuts straight to the heart of good guitar amp recording technique, and is based on a day-long discussion with Mark at Studios 301 in Sydney, which was kind enough to allow us the use of the recording space for the day.
Guitar Miking 1

Miking Guitar Amps
Mark Opitz: Okay. The first thing I want to show you is my reliable and, dare I say it, infallible mic technique for capturing the sound of a guitar amp. After I hit on this technique quite by accident years ago, my days of placing mics all over the amp and the room in the blind hope of capturing a magical guitar amp sound were over. Although I don't expect people to drop everything they've been doing for this approach, for those of you who are less than convinced by your own guitar amp recording technique, this may be the solution to your dilemma.
I should start by saying that this technique in principle works regardless of the amp in question, whether it is small or large, loud or quiet, a Marshall or Fender. We're only using a small, single-speaker amp for the purposes of this demonstration here (because that's all we could find kicking around 301!), but this system is applicable to any amp, whether it be a Marshall quad box or a Fender Deluxe. The only difference is that if our demonstration amp contained more than one speaker, we'd first choose the best speaker in that box. In this case obviously there's only one, so we can skip that process.
You'll notice we've put a Shure SM57 dynamic in front of the amp, as well as an AKG C414 large diaphragm condenser – two quite different sounding mics. Our setup involves these two mics placed at 90 degrees to one another (the 90 degree angle helps maintain the integrity of the phase relationship). Unlike most single or multiple mic setups I see people constructing in the studio, you'll notice that the two mics are placed on the imaginary line that marks the centre of the speaker cone. I do this so we're capturing the top end from the centre of the speaker, but without facing the mic directly at it. Both mics are effectively at 45 degrees to the top end source (see below) whilst directly facing the body of the speaker cone. That way we're capturing the top end in both microphones, but without a sharp, unnaturally bright edge to the sound that can be produced by pointing the mic directly at the speaker. We're also facing directly at the bottom end emanating from the speaker. In an X/Y configuration, where the two capsules are exactly the same distance from the speaker and inside the radius of the speaker (i.e., closer to the speaker than the distance from the centre of the speaker to its outer edge), the mics will effectively be facing the two sides of the inwardly projecting paper cone.
Guitar Miking 2

The reason we're using two microphones here is one of those happy accidents I came across in the '80s when I was testing different microphones. At the time I was using a Sennheiser 421 and an AKG C414, but in the end I found the Shure SM57 worked better in this setup. Being a dynamic microphone, its mid-range is very, very good. The AKG C414 condenser complements the 57 by capturing top end and bottom end that the 57 can't hear. So the effect you're getting is like a dovetailing of the two microphone tones. If you want, you can use a Neumann U87 or a U47 Fet (or any large diaphragm condenser, provided it can cope with high SPL), but the reason I use the AKG is because it's probably one of the toughest condensers ever made and, as you know, amps get loud! The AKG also has a 10dB pad on the microphone, so I'll always pad it down – and always at the mic, never at the desk. If you're dealing with a blisteringly loud amp like a quad box turned up to '11' you need something that's going to be able to handle that sort of power. We know the SM57 can handle it, we see them on stage on amps and drums all the time.
Once the mics are placed in their visually correct position, never assume that because a mic's placement looks right it's going to sound right. Make sure they're working by bringing them up in the control room monitors panned to the centre (mono). Once the two mics are at similar volumes in the monitoring, flip one out of phase and fine tune their positioning until they start to substantially cancel each other out (the out of phase character should sound thin and horrible compared to the in-phase tone). Then flip them back in phase and bang! There's your guitar sound. I've always found that this particular miking technique is instantly effective. One thing I can't stand in the studio is arsing about getting a guitar sound, putting mics here, there and everywhere, trying different rooms and different mics. With this setup the sound you get out of the amp is exactly the same as the one you'll get in the control room. And that's always the hardest part in getting a good amp sound – simply capturing a sound that's true to the amp.
AudioTechnology: Can you describe in plain English why the two mics are placed at 90 degrees to one another?
Mark Opitz: It's because basically you want the signal hitting the diaphragm of each microphone at exactly the same time, i.e., phase coherently. Difference in phase, as most people would realise, is brought about by a discrepancy in distance between two or more microphones, a source and its capture – different lengths create different times.
AudioTechnology: Do these two mics usually act as one in terms of the mix? Meaning, were these mics sub-mixed down to one track on tape in the past?
Mark Opitz: Well, that's what I used to do – but not so much these days because you've got lots and lots of tracks in the digital domain usually – but if you're going to analogue tape I'd nearly always send the two mics to one track instead of keeping them separate. In digital multitracking, where there's typically a plethora of tracks to work with, there are two things that I often do. One is, I put them on separate tracks because that enables us even further manipulation of the phase, by blowing up the wave form and tightening the in-phase characteristics. Although with this technique, nine times out of 10 when we blow it up it's okay anyway. Another thing I always do now digitally is record a DI of the sound, but not for re-amping purposes. I do that for editing purposes. Of course it's good for re-amping, but more importantly, if you're editing a guitar track in a digital situation, to pick up the front end of the note it's much easier to hear it off a clean DI sound than it is from a heavy distorted sound. The waveform is far better represented as well. So, for instance, if you're editing you can listen to the DI and drag the mic channels around with it.
AudioTechnology: When you're miking an amp with several speakers, does this technique always disregard the other speakers in the cabinet?
Mark Opitz: Always. Here we're using an amp that only has one speaker. On a quad box, however, it's a little different. You're still only miking the one speaker, but the trick with the quad box is to find the right speaker. It's amazing how many guitar players don't realise that some of their speakers are not sounding as good as the others. And that can be determined, once you're experienced with the technique, before a note's played by examining the hiss that's coming out of them. Years ago, for example, with AC/DC, I used to go through their whole rig, trying every Marshall head and every speaker box. I think every guitarist in the band had about four Marshall heads and eight boxes and on that particular album, Powerage, I went through and matched every head against every speaker until I found the right combination. And that's not every speaker box, but every speaker! It took nearly two weeks to do.
AudioTechnology: Is this with them in the room waiting for you to hit record?
Mark Opitz: [laughs] No, no. I had two weeks preparation beforehand, and that's the whole secret to everything, the only magic trick – preparation. Actually, in that particular situation I didn't use this technique then, I just used a good old Fet 47. That record predates this technique.
The thing about this X/Y technique is that you can play with it too – as long as you adhere to the principle and play within it. You can go right up against the centre of the cone or back the mics away... just so long as they remain in an X/Y setup and centred on the speaker. One of the crucial factors is that the mics must remain set up in front of the centre of the speaker cone. Otherwise the technique won't work. It's got to be dead centre, that's the whole thing. What's coming out of the centre of the cone and the edges of the cone has to reach the diaphragm of each mic at the same time. That's how you get perfect phase. And when you look at the setup it's actually incredibly simple and quick, which instills confidence in what the players are doing and confidence in the engineer.
But sometimes a close-miked amp sound is simply not the order of the day, and in that situation I'll often add a Neumann U47 Fet placed at distance to back up this approach, rather than abandon it altogether. The only reason to add this mic is if you're trying to get extra room ambience into the sound.
Guitar Miking 3

AudioTechnology: Wouldn't it perhaps be easier just to move the 57 and the 414 back a bit than have that third mic messing up the phase relationship?
Mark Opitz: Exactly, but not too far back because you've got to remember once you start moving back the focal length of the speaker's going to change. We're relying here on the physical aspects of the speaker. You can only work in the confines of the speaker setup, and there's really only a 10 to 20 percent leeway to work with. You can't drop them back as far as the placement of the U47. Get a torch, look at the grille, set the mics up so the centre of the X/Y configuration is right on the imaginary centre line, turn on the amp, start playing, end of story. It's very simple.
Thanks again to Mark Opitz and Studios 301

Elantric


In this clip I compare 27 Celestion 12 inch guitar speakers. I'm using a 2013 Gibson Les Paul SG Custom Shop Aged and a 1982 Marshall JCM800 4104. The Speakers are all mounted in the same Cabinet, an all ply Marshall JCM800 1933 1x12 closed back. It was recorded using one1960s BeyerDynamic M160 Ribbon Microphone. The soundinterface is an Apogee Duet and the DAW is an Ipad with Cubasis. The 4104 JCM800 Amp settings are: preamp 2, master 1, bass 2.5, treble 6, mid 10, prescense 7, high input jack. Recorded dry at low volume. Thus it can be argued that speaker distortion necessary to bring out the character of the different may not develop, especially for the higher watt models. I do however believe that this test gives a fair estimate on how the speaker relate to each other.

The speakers are:

1. 1983 G12H-100
2. 2013 G12K-100
3. 1973 G12H-30 55Hz T1281, Pulsonic
4. 2014 G12H-30 55Hz Heritage
5. 1971 G12H-30 55Hz T1281, Pulsonic (May be Pre Rola)
6. 1976 G12H-30 55Hz T1281, Kurt Mueller, "Black Back"
7. 1970 G12M-25 75Hz T1221, Pulsonic, Pre Rola
8. 1995 G12M-25 75Hz Reissue
9. 1980 G12-65, 1777
10. 2014 G12-65 Heritage
11. 1982 G12-65, 1777
12. 1971 G12H-30 75Hz, Pulsonic, Pre Rola
13. 1974 G12H-30 75Hz, Pulsonic, "GreyBack"
14. 1978 G12-80, 1777
15. 2014 Classic Lead 80 (G12-80), 1777
16. 1993 G12-80, 1777
17. 1965 AlNiCo Silver B025
18. 1988 Vintage 30, 444
19. 2013 Vintage 30, 444
20. 1989 G12M-70
21. 1987 G12T-75
22. 2010 G12T-75
23. 1999 G12T-75
24. 1979 G12-125
25. 1991 G12B-150
26. 1993 G12T-100
27. G12F-60, RockDriver Junior.

Beirne

Or you could just go direct. And model the speaker room etc with guitarrig or something.
www.intangiblesny.com
www.facebook.com/intangiblesband

Elantric

#3
True - but the "28 Celestion speakers" Youtube video swiftly demonstrates the audio character of each model to untrained ears.

Folks should know the difference between a Vintage 30 vs a G12-80




plexified


This is an art and not one to learn in a studio while your on the clock paying for it. The two mic standard is an outstanding presentation and an example of collecting as much data as you can before the DAW. I'll throw down some data to further this along, since time is money here. The more pristine the guitar tone the more attention you want to spend on the pre. Below is a video that goes into this concept on the other side of the fence with dirty tones and successful strategies from four high level producers.

Although we often think of front mic, always consider rear mic as well. In both cases if your close mic, you want to isolate from room reflection. Here 'tenting' is used. where a cover is placed over the mic to keep away stray reflection, which is very important. While we are here, I suggest no grille cloth when possible, its a noise source. Remove the grille if you can. Or use ISO boxes as the last article below demonstrates. They offer repeatable fixtures that you can also use for FOH live. The rear mic technique requires proper phase alignment and doubles your tone source. For instance I use a Vox Bulldog and a Jensen P-12R in a Fender Twin combo. Here you get 4 different speaker sources and 8 when using two mics significantly affording many options before EQ as demonstrated below.

In the case of the last example on the OP above, the single mic can be replaced with a Sure SM-81 shotgun style for a very usable tone for anything from acoustic, bell like Strat tones or even Metal. Its a very valuable option.

https://www.youtube.com/watch?v=gaSrXimH3ZI&t=5s&index=43&list=PLXmwQZcfhFf-XKR3k4EqVkZEnFABsuRYT

ISO Box : http://theguitarzombie.blogspot.com/search/label/isolation%20cab

plexified

#5
Here is a pro walk through  by Eric Valentine in his LA studio on how he recorded several of the Slash Albums. He is a very experienced engineer so don't let his youthful glow fool you. In this outstanding walk through, Eric outlines how he used his technique amongst others to  recorded several Slash albums, including while Marshall was Engineering the Slash model at the same time. The proto type is in the examples.

So the quick points are Eric uses the 'convergence' technique I  pointed out in addition to three other mic techniques. This is a convergence example where he center mics the 4x12 sweet spot to capture all 4 cones at the same time at distance. It affords tremendous texture and if you have ever seen a 4x12 at full volume the cones resonate and react to the cab and the room, so you can almost 'see' waves and that all the cones do not move exactly the same, hence the texture. This is of course in addition to speaker tolerances. Eric has this mic set up on a 'mic robot' where he can move and tune it from the control room, very cool.

A few other points is that he has a chalk mark on the Slash 4x12. Its a circle that marks the cone centers of all 4 speakers and indicates the inside of the 'convergence of the cones.  Ok, so Eric goes into much greater detail with some good stories, including the origins of Slash amps and mods. If you want more info, let me know and I will link the epic research. Enjoy. Edit: Just wanted to point out that Eric is using a Royer 121 and Time Pierce uses a Royer 122V. Royer is Very popular right now.