Recording question/help

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nhennies
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Recording question/help

Post by nhennies »

I'm hoping some of you engineering and/or acoustics experts out there might be able to help me with something.

I'm trying to record a long section of a piece that involves playing very high notes on the vibraphone at a pretty high volume. When I do this I can hear very pronounced lower difference tones but when I try to record it I no longer hear them. What is the reason for this, and is there any way to capture them on a recording? It could be as simple as my mics aren't good enough or something (I'm using a decent matched stereo pair of small condensers) but I honestly have no idea.

Anyone?

Dan Bennett
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Re: Recording question/help

Post by Dan Bennett »

Difference tones are highly positional - because they're a product of the interference of waveforms they will appear in certain places but not others - and where will depend on the wavelengths of the sounds in question and the room you're in.

The only way to be sure of capturing them is to get a friend to hammer the notes while you wear closed back headphones monitoring the signal from the mics. Move the microphones around until you hear the difference tone - it's a faff, but eventually you'll find the correct mic placement.
Also, it's maybe a good idea to start without the mics - have your friend hammer away while you just move your head around. Try to be aware of the ear in which you're noticing the difference tones. Then use that rough area for your mic placement.

If you're on your own you could try sticking the mics up by your ears, but it's probably difficult to position them exactly right especially if you need to be where they are while playing.

Another interesting option is to wear binaural mics in your ears - you can then "play" the mics by moving your head around. Though in some cases, because of the tiny difference in position between your ears and the mic, this might still not be enough.

The "moving mics around, listening on headphones" option is the most reliable.
Last edited by Dan Bennett on Wed Apr 06, 2011 6:48 pm, edited 1 time in total.

nhennies
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Re: Recording question/help

Post by nhennies »

Awesome, thank you very much.

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bryan
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Re: Recording question/help

Post by bryan »

Dan Bennett wrote:The "moving mics around, listening on headphones" option is the most reliable.
Yes, that's good advice. It could be that the stereo condensers need to be in just the right sweet spot, and not just that, but the angle of the mics with respect to the sound source, otherwise phase cancellation could be killing the frequency relationship that's producing the difference tones.

If you're working with sound files on a computer then you can check the phase of the stereo pair and nudge the L or R channel foreward or backward with respect to the other.

Last resort: add a close mic that you can mix in with your main stereo pair.. EQ and mix in close mic so that it targets the frequency that brings out the difference tones.

Good luck, let us know how it goes.

Dan Bennett
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Re: Recording question/help

Post by Dan Bennett »

Out of interest, how'd you get on with this?

nhennies
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Re: Recording question/help

Post by nhennies »

I haven't had a chance to work more with this yet because of a very busy work and rehearsal schedule right now. I got some very good advice from another engineer friend too who also suggested the use of omni mics rather than directional ones (among many other great ideas). I'll be sure to let you guys know when/if I pull it off. Probably next month sometime.

Thanks again, everybody.