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Stereo recording
Old 27th February 2014
  #1
Question Stereo recording

Hi guys,

I've found a nice stereo acoustic guitar sound using my Behringer B-2 Pro recording one track with the mic horizontal looking at the sound hole, and another track with it angled upwards approximately 40 degrees, but turned to still look directly at the sound hole. Both have a radial distance of ~40cm and are set to cardioid. Surprisingly, it's not too boomy, and there's a nice room reverb.

The thing is, I only own one of these mics, so I need to record the two tracks with identical timing/strokes, which is a hell of a challenge. It sounds very good IMO, but there's always one or two strikes that I miss on one side, and they stand out like sore thumbs.

Has anyone ever recorded like this to emulate a stereo mic'ed guitar and had good results? Also, would it be a good idea to purchase another B-2 to save on the effort? Is it risky to buy another mic, as opposed to buying a matched pair for the job?

Cheers
Old 27th February 2014
  #2
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Lotus 7's Avatar
Behringer does not offer a matching service on their mics, so just buying another one (of the exact same model) will likely result in having a pair that will be as close as if you bought them at the same time. For recording a single instrument like a guitar, close matching is not really necessary. In fact, some guitarists like using different mics at different positions on a guitar. It's a commonly used technique. A LDC near the sound-hole and a brighter, "peakier" mic like a SM-57 near the fingerboard can work.

Matched pairs of SDC mics are sometimes used to achieve the most accurate stereo localization when a XY , ORTF, NOS. etc array is used for ensemble recording. For a single instrument it's not as important.

Recording two separate tracks or "doubling" a recoding can create an interesting sound, but it will never be the same (or even close) to a true stereo recording because of the precise phase relationships in the stereo tracks that are impossible to achieve in two separate takes. If you like the sound of the "doubled" single-mic tracks, the same can be done using doubled stereo recording.

Another technique you may like is to record a single track and then duplicate it. The second track can be delayed a few milliseconds (try 5-10 mS to start), and then equalized so as to have a few broad peaks and a few broad dips (keep them gentle, maybe +/- 3 dB) so as to be different from the original. Playing the two tracks together with one panned slightly right an the other panned slightly left will give a good approximation of the doubling you're getting now, but without the missed strikes.

If you an borrow another mic (any mic), don't be afraid to try it with your B2 Pro in stereo. You can't hurt anything and you may be pleased with the effect. It won't be balanced stereo, but can result in a good sounding track. Also, remember that the closer you position two mics the more important it is to check for phase interference if you want mono compatibility. It's easy to get "phasing" issues if a stereo track is mixed down to mono if the mics aren't positioned correctly. In stereo, the phase differences between the mics will add to the apparent "spread" or "width" of the guitar's stereo image. A pair of close-spaced mics will create a stereo guitar acoustic image that spans the full distance between your monitors, but can, of course, be reduced by using your pan controls as needed. Unless you like the idea of a 8 ft wide guitar.
Old 27th February 2014 | Show parent
  #3
Quote:
Originally Posted by Lotus 7 ➡️
Behringer does not offer a matching service on their mics, so just buying another one (of the exact same model) will likely result in having a pair that will be as close as if you bought them at the same time. For recording a single instrument like a guitar, close matching is not really necessary. In fact, some guitarists like using different mics at different positions on a guitar. It's a commonly used technique. A LDC near the sound-hole and a brighter, "peakier" mic like a SM-57 near the fingerboard can work.
Thanks for the detailed answer! I was going to ask if anyone has used completely different microphones as part of a stereo recording for acoustic guitar, but I was thinking I'd get laughed at!

My collection of microphones contains the Behringer B-2 Pro, an AKG C214, an SM57 and a "matched pair" of Behringer C2 SDCs, although I don't think they're very good; they have almost no bass response at all, except when exploiting the proximity effect. Are all SDCs like this? The C214 sounds too tinny when I strike the strings, unless I take it well away from the sound hole.
Old 27th February 2014 | Show parent
  #4
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Lotus 7's Avatar
Quote:
Originally Posted by adamd1008 ➡️
Thanks for the detailed answer! I was going to ask if anyone has used completely different microphones as part of a stereo recording for acoustic guitar, but I was thinking I'd get laughed at!

My collection of microphones contains the Behringer B-2 Pro, an AKG C214, an SM57 and a "matched pair" of Behringer C2 SDCs, although I don't think they're very good; they have almost no bass response at all, except when exploiting the proximity effect. Are all SDCs like this? The C214 sounds too tinny when I strike the strings, unless I take it well away from the sound hole.
Don't know about the C2's but mics can be different as night and day. Very generally SDCs with cardioid polar patterns will be pressure gradient designs. Those will inherently will have a gradual roll off below about 100 Hz at distances of a meter or more, and a proximity effect boost up close. Some have more roll-off than others. Typically, the "tighter" the pick up pattern, the more roll-off. Schoeps CMC64s (cardioids) are fairly flat to 40 Hz and work down to 30 Hz.

Omni SDCs can be, and often are flat to very low frequencies. I use Sennheiser MKH8020s and those are flat down to 10Hz and actually will record sound as low as 5 Hz. Absolutely no bass roll-off and no proximity effect. Great for recording air-handler noise!

You might try applying some EQ to the C214 to try to match the B-2 Pro sound. The C214 has the typical AKG dip at about 1600Hz and a big vocal brightening ramp-up from 6k to 13k. A broad (Q=0.5) + 3dB boost at 1.6k, and a very broad (Q= 0.33) drop of -5 dB at 9k will flatten it out and may remove some of the "tinny" sound.
Old 28th February 2014
  #5
I'll start looking into some omnidirectional SDCs then! I just looked at the price of the MKH8020, and... are all decent omni SDCs really expensive? I've noticed Behringer do a cheap one, but I'm reluctant to go with them due to things we've already discussed. Could you recommend anything? I've heard good things about the Oktavia 012s.

The concept of an omni SDC has always confused me, because the mic would have to listen through itself, from behind... Anyway, I'll also try what you suggested with the C214
Old 28th February 2014
  #6
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I've had good luck recording my acoustic guitar with mis-matched mics, but if you want to use a matched pair, AKG 451s are one of my favorite SDCs. A bit spendy though. You can put different capsules on them - omni, cardioid, supercardoid...

Here's a mic shootout with some SDCs including the 451s



You might also want to do some research on "mid-side" micing techniques.
Old 28th February 2014 | Show parent
  #7
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Lotus 7's Avatar
Quote:
Originally Posted by adamd1008 ➡️
I'll start looking into some omnidirectional SDCs then! I just looked at the price of the MKH8020, and... are all decent omni SDCs really expensive? I've noticed Behringer do a cheap one, but I'm reluctant to go with them due to things we've already discussed. Could you recommend anything? I've heard good things about the Oktavia 012s.

The concept of an omni SDC has always confused me, because the mic would have to listen through itself, from behind... Anyway, I'll also try what you suggested with the C214
Warning: long rambling post, read at your own risk.

Cardioid vs Omni patterns:

Another way to think about it: Both a cardioid and an omni mic pick up the direct sound radiating from a source (the instrument) AND reflections from the room walls, ceiling and floor. The difference is that the omni picks up more reflected sound (but, not less direct sound). At any given distance, either mic pattern will pick up some direct sound and some reflected sound.

In any room there is a positioning point where the amount of direct and reflected sound is equal. In acoustic physics, that point is called the critical distance. The critical distance will obviously be different for a cardioid mic vs an omni. For an accurate, pleasing sound with a reasonable, but not excessive amount of room reverberation, the generally used source to mic distance for a cardioid mic can be up to 0.5 X the critical distance. However, for an almost identical ratio of direct to reverberant sound, an omni must be placed no farther than 0.3 X the (cardioid) critical distance.

That means that in any given room and mic spacing a omni will sound very much like a cardioid when placed at 60% of the distance a cardioid was placed at. (0.3/0.5 = 60%) as long as both are placed at less then the critical distance. Omni's just need to be positioned closer to the instrument. A cardioid mic is not a "spotlight", it has an almost "hemispherical" pick up pattern, the omni has a full "sphere" pattern.

Re: "the mic listening through itself": Because the wavelengths of sound involved are much larger than the physical dimensions of the mic, and because most omnis are pure pressure transducers, the sound is picked up perfectly well by the pressure waves that move around the mic. For a small diameter SDC**, the mic body does not "shadow" the sound at all until you reach supersonic frequencies.

**Some SDC manufacturers make accessories for their omnis which modify the rear pick up pattern at high frequencies and essentially cause the mic to have a more directional pattern at high frequencies, rejecting sound from the sides and rear. DPA calls their accessory "add-ons" Acoustic Pressure Equalisers and they come in different sizes having different frequencies above which they become directional.

High-performance SDC's:

The Sennheiser MHK Series, Schoeps Collette Series and DPA omni mics are "state of the art" SDCs and "the very best" is always expensive. I currently own and use them all for classical recording. The Oktava Mk-012 have a good reputation and the multi-capsule sets are a great buy at their price point.

A couple of very fine mics that IMHO are fantastic bargains and are "cleaner" than the MK-012 omni capsules, if one is looking for an accurate, transparent microphone (no coloration added) are the Line Audio SDC's The Line Audio CM3 (wide-cardioid pattern) has a good following on Gearslutz. I use them for large choral work, currently have (6) and have found them to be excellent. Each is identical to the others (they are essentially "matched"). (See the never-ending Gearslutz CM3 thread) Like other pressure gradient cardioids, they have the characteristic bass roll-off.

The Line Audio OM1 (omni pattern) is flat to sub-sonic frequencies. If you have a decent sounding room and/or can position the mic close to your instrument, the OM1 may be worth a try. The OM1s are excellent, professional grade mics at a very low price.

The Line Audio mics are hand assembled and tested by Roger Jönsson in Sweden, and can be ordered directly from him or from NoHype Audio in Belgium. It's not as convenient or as fast as ordering from a retailer like Sweetwater, Full Compass or Musician's Friend, but the slight extra effort is rewarded by you're being able to purchase a mic for about 1/3 rd the cost of what it would sell for at one of the retail dealers. IMHO, there are no mics costing less than US$600 (new) that out perform the CM3 and OM1.

Roger is an excellent designer and engineer and is completely trustworthy. You send him an order, he makes a mic for you, you pay for it by bank transfer, an he sends the mic right away. It only takes a couple of weeks, and you don't have to even speak Swedish! I haven't ever used the Belgium dealer since, for a US purchase, it's not any different than dealing with the designer directly. Buying directly from Roger, you're guaranteed to get a nice warm mic right out of the oven.

I have no affiliation with Line Audio, but am a very satisfied customer. The "hand assembled in Sweden" LA mics are in a different league than the "mass produced in China" Behringers.
Old 1st March 2014 | Show parent
  #8
Quote:
Originally Posted by Scooter Trash ➡️
I've had good luck recording my acoustic guitar with mis-matched mics, but if you want to use a matched pair, AKG 451s are one of my favorite SDCs. A bit spendy though. You can put different capsules on them - omni, cardioid, supercardoid...

Here's a mic shootout with some SDCs including the 451s



You might also want to do some research on "mid-side" micing techniques.
Thanks, I'll be looking into that! I might need a better budget though!

My favourite, from that video, is the NT5. I think they have just the right amount of 'boominess' and twang.

Quote:
Originally Posted by Lotus 7 ➡️
A couple of very fine mics that IMHO are fantastic bargains and are "cleaner" than the MK-012 omni capsules, if one is looking for an accurate, transparent microphone (no coloration added) are the Line Audio SDC's The Line Audio CM3 (wide-cardioid pattern) has a good following on Gearslutz. I use them for large choral work, currently have (6) and have found them to be excellent. Each is identical to the others (they are essentially "matched"). (See the never-ending Gearslutz CM3 thread) Like other pressure gradient cardioids, they have the characteristic bass roll-off.

The Line Audio OM1 (omni pattern) is flat to sub-sonic frequencies. If you have a decent sounding room and/or can position the mic close to your instrument, the OM1 may be worth a try. The OM1s are excellent, professional grade mics at a very low price.

The Line Audio mics are hand assembled and tested by Roger Jönsson in Sweden, and can be ordered directly from him or from NoHype Audio in Belgium. It's not as convenient or as fast as ordering from a retailer like Sweetwater, Full Compass or Musician's Friend, but the slight extra effort is rewarded by you're being able to purchase a mic for about 1/3 rd the cost of what it would sell for at one of the retail dealers. IMHO, there are no mics costing less than US$600 (new) that out perform the CM3 and OM1.

Roger is an excellent designer and engineer and is completely trustworthy. You send him an order, he makes a mic for you, you pay for it by bank transfer, an he sends the mic right away. It only takes a couple of weeks, and you don't have to even speak Swedish! I haven't ever used the Belgium dealer since, for a US purchase, it's not any different than dealing with the designer directly. Buying directly from Roger, you're guaranteed to get a nice warm mic right out of the oven.

I have no affiliation with Line Audio, but am a very satisfied customer. The "hand assembled in Sweden" LA mics are in a different league than the "mass produced in China" Behringers.
Wow, I can't thank you enough for your super detailed answers, of which I'm very thankful!

I agree with your point about mass-produced products are in a much lower league than hand-assembled ones. There's undoubtedly more heart and soul put into them. I will certainly be looking into Line Audio, which seem very attractive and affordable.

There's one thing though, and I fear the answer is, "it depends": you said that you use the sub-cardioid mics for large choral work, whereas you mention the omnidirectional mics in the context of recording an instrument. Are you suggesting that, ultimately, assuming room reverberance is good, omnidirectional mics will always be best for recording stereo acoustic guitar, given that I like a good bass response, as though the guitar is the main part of a whole track?

Thanks!
Old 1st March 2014
  #9
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Lotus 7's Avatar
Assuming normal guitar tuning, the lowest fundamental (E) will be just over 82 Hz. For direct sound (the "on-axis" sound waves reaching the mic directly from the guitar - no reflections), any mic that is flat, and has no major phase shift down to 80 Hz will not have any apparent bass roll-off of the lowest note on a guitar. Does not matter if it's a cardioid or a omni pattern. Some cardioids may start their bass roll-off as high as 150 Hz with 100 to 120 Hz being common. At 80 Hz the drop may be only 3 or 4 dB, but it can begin to "thin" the guitar's low end a little.

The situation is somewhat different for reflected sound and directional mics (wide-cardioid, classic cardioid or hyper-cardioid). For those mics, the off axis, reflected sounds are picked up at different sensitivities for different frequencies. That can create a thin, tinney "bad room" effect that hurts the overall sound when added to the direct sound.

Pure pressure mics (SDC omnis) will almost always have a very consistent frequency response function at all angles. The frequency spectrum of the off-axis, reverberant sound is the same as the direct sound, so if the room is decent, the overall sound is more accurate and more like the actual sound of the instrument.

Remember, a lot depends on what you think your instrument should sound like. The sound that reaches your ears while you are playing, is quite different than the sound hitting a mic placed in front of the instrument. The sound you envision in your mind may be much different than than actual sound you're producing. Sound that seems low on bass to you may actually be quite accurate, and some carefully applied "ramping" EQ may be all you need to get the sound you envision.

I've used the wide-cardioid mics for choirs that occupy a space 30 feet wide and 6 feet deep, and need 4 to 6 mics for uniform coverage. To get that coverage (usually in a very reverberant space), the mics must be placed at least 5 or 6 feet away from the singers. Omnis would have too much off-axis pick up to use in that situation. Recording a single guitar in a smaller, less reverberant space, with up close positioning is a dramatically different situation.

Most engineers who record classical instruments or classical ensembles will usually favor using AB spaced omnis, if the room is reasonably good sounding. Personally, it's my preferred choice. If the room is not great, or if it's a live performance with audience (behind the mics), then I will usually go to a pair of standard cardioids in a NOS configuration, and often add close cardioid "spots" on some instruments. For a string quartet, it's sometimes possible to get a decent recording with just a spaced pair of omnis, or a spaced XY NOS set of cardioids. For a piano trio, I almost always have to add a spot on the piano to keep it from sounding too distant, and a spot on the cello to get the right balance.

So, you're right: "It all depends".
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