Topic: TSKB: Picking up low frequency sounds

[macroint]

>my only thing is that the mic recording technique might not
>suffice a lot of this stuff, probably not joes either. i dont think his mics
>will pick up the low freqs, mention that to him and see what he thinks.

The above is from an e-mail I received about taping a show. All of the acts use a computer and other assorted electronics, which apparently emit low frequency sounds that microphones typically won't catch. Or will they? I don't know squat about anything, which is why I'm tapping the knowledge bank.

I use Peluso mics...is there anything I can do to ensure that I'm able to pick up low frequency sounds?

[Krispy D]

the CMC6/MK4 has a frequency response of 19Hz/25Khz.  Just how low a frequency are we talking here? I would imagine that if you can hear it the mic will record it.

[Gutbucket]

Your Pelusos should be fine.  They may be referring to typical dynamic stage mics used to close-mic guitar cabinets, vox and such, most of which roll off the lower frequencies significantly.  The condensers we use for music recording have a flatter frequency response.  The low end does roll off the more directional the pattern gets (which can be useful if the bass is overly strong) so if you want the flattest response down low, use omnis if you have 'em and no high pass filter.  You'll get bass'o'plenty.  Pipe organ is the low frequency king of the acoustic world and omnis are a primary choice for them to get the earth moving thunder of the instrument.  Electronic music can be very loud in the bass region but probably won't actually go as low as pipe organ due to the low frequency cut off of the FOH subs.  Very low frequencies interact strongly with the room and so your position in the room becomes important due to  'room modes' or standing waves canceling and reinforcing as you move around the room.. not that your position in the room isn't important for other reasons, but you knew that.  

[edit- apologies if you knew this stuff already]

[Craig T]

You'll be fine.  You may even find yourself wanting to cut some of the low freq with some EQ - this has been the case with some bands I've recorded that use a lot of bass synth/fx.

[easy jim]

^ what they said.  Accurate playback of frequencies below 50Hz on most playback systems is a much more common issue than the ability of the condensor mics we typically use to capture those frequencies below 50Hz.  Below 40-30Hz or so, you 'feel' it much more than 'hear' it.  Too much going on below 40-50Hz makes for a recording very unfriendly to playback on most systems, and is the reason why I've blown many car speakers listening to analog tapes of old GD FOB and section recordings.

[Gutbucket]

^^^
Note the omni polar avatar.   

Sometimes it's a question of quality over quantity, a perceptual thing.  A great recording conveys the perception of the bass even on a system that can't reproduce the lowest couple octaves.  Luckily the brain fills in the missing bottom, unlike for the top end.  Boom boxes, clock radios, TV speakers, and desktop systems roll of way higher than 40hz but still can sound good and the kick drum and bass guitar doesn't disappear to the ear.  You won't feel the bass in your chest like at the show, but hopefully you don't perceive it as missing either.

But if the vibe and heart of the music is in that electronic bass instrument, it might be a good idea to make optimizing the sound of the bass on the recording a higher priority than other considerations like image. Spacing the mics wider can get more of a stereo feel at lower frequencies and less directional capsules can make the bottom sort of 'open up' for lack of better words, so that could be an option unless you need more directional mics to deal with realities of the room and mic position. 

[macroint]

Thanks to all.

[DSatz]

Hi. Yes, pressure microphones (which are omnis) generally pick up more bass, and deeper bass, than pressure-gradient microphones (which are generally directional microphones).

But pickup of low-frequency sound is very room- and position-dependent as well as microphone-dependent. There's an acoustical phenomenon called "standing waves" which basically means that certain frequencies, which are related by their wavelengths to the dimensions of the space you're in, will have definite positions in the room where they're strong and other positions where they're weak. (This affects both recording spaces and playback spaces, so when you play back a recording over loudspeakers, you get both.)

Now think for a moment about the way people use omnis (which normally have to be spaced apart in order to get any stereo effect at all) vs. directional microphones (which are most often coincident or closely-spaced) and you'll see that in a spaced pair, you're "sampling" the conditions in two distinct places in the room, while with a coincident or closely-spaced pair, you're not getting much if any differentiation between channels in terms of the standing waves in the room. Also, directional microphones, by the mere fact of having one or more "null" pickup angles, filter out any standing waves that arrive at or near those angles. So one potentially large source of "cues" about the nature of the acoustic space can be lost.

Some people really don't like having distinctly different low-frequency behavior in the two channels, but it can be interesting sounding, and it could very well be a feeling that some people would miss when they don't get it from a recording. Those people will usually gravitate toward recording with spaced microphones.

--best regards

P.S.: Conceptually as well as physically, a cardioid is halfway between a pressure transducer and a pressure-gradient transducer. A pure pressure-gradient transducer would be a figure-8. It's a long-established convention to use the word "pressure gradient" to cover all the in-between patterns (cardioid, hypercardioid, supercardioid, wide cardioid, and now "Open Cardioid") as well--but strictly speaking, that is really only true for variable-pattern dual-diaphragm capsules (e.g. a Neumann U 87 or AKG C 414 operates as a pressure-gradient microphone even when its pattern switch is set to the "omni" position--you can even hear some proximity effect).

A single-diaphragm capsule with any of the in-between patterns--including cardioid--functions partly as a pressure transducer and partly as a pressure-gradient transducer. Its characteristics will depend on the mixture of these two principles that produces its directional pattern. A supercardioid, for example, has a higher proportion of its sensitivity due to pressure-gradient pickup, while a wide cardioid is the opposite.