re: Recording LF (and ultrasound)

["Ryan Reid" <ryanreidfl@gmail.com>]

Mech wrote:
>you should keep in mind that there aren't too many pieces of analog
>equipment (and I'm talking physical things like mics, speakers, and
>even cables) that can really fully transmit frequencies above about 60khz,
>so 192k might be a little overkill.  :)

Well, I should have been more specific - I meant a 192khz sample rate
in recording, so that Nyquist wouldn't clamp things too much, and so
that recordings could be pitched down to audible range without
significant aliasing. I first plugged my (now in need of a fuse from a
unrelated accident :/ ) signal generator direct into my Focusrite
Saffire I/O. NOT RECOMMENDED WITHOUT A 1:1 WIDEBAND TRANSFORMER but it
went alright for me. I didn't pitch this down, but just viewed a sweep
in Adobe Audition's spectral display. Sure enough, it made it up to
around 90kHz, though of course with signal loss and noise. I then
tried my M-Audio condenser mic on a few instruments and household
sounds. Not many ultrasonic harmonics showed up except in percussive
transients - my glockenspiel struck with metal mallets really spiked
up there. An electric toothbrush showed a nice range.

Unfortunately, I conducted all of this in a hurry while needing to get
back to work writing a paper, so I couldn't be too thorough. What is
certain is that recording at 192khz and pitching down provides some
amazing results - my piano simply sounded as though it had been played
at a lower octave, the glockenspiel changed into gorgeous bells (sans
the harsh transients - will use rubber/cloth-covered mallets next
time), and the toothbrush turned into an absolutely convincing
helicopter - the mic's proximity effect providing full-on doppler
effect. I should have a few ultrasonic transducers in the mail
sometime this week actually and hope to do some more exploring - I
imagine I'll get a lot more sticking them outside the window than from
anywhere inside. We'll just have to wait and see. Unfortunately, I
don't have a laptop or decent portable recorder to go on any full-on
expeditions with at the moment.

As for the woofer mic, I haven't done much testing yet. I don't
actually have many bassy instruments and it was more to have fun with,
and perhaps getting some low end vocals for multitracking. I was
mistaken earlier - it's actually a 5" woofer from an old Altec Lansing
computer sub. I mounted it into a PVC joint with the plan of stuffing
the inside with foam before sealing. Oddly enough, I got a lot more
volume from the magnet-end of the mic, even with foam in front of it!
I'm not sure why that is, but I'll just have to play with it some
more. Will report later! I'd had the idea before, but got motivated
when I saw this: http://theogre.home.bresnan.net/kickit

Take care,
Ryan