High Frequency AC Bias - Acoustic

[space2012]

get audix cx-112
or that russian tube & transformer microphone.

that makes me wonder if hard drives have a bias?

Micropnone
Mic Tests
What's your favorite vocal mic?

[stinkyfingers]

what?

[williamsharkey]

Allow me to clarify:

I would like someone who is capable of measuring noise to perform an experiment; record a sound with a mic normally, then once more while emitting ultrasonic noise into the room.

Hypothesis:

The presence of ultrasonic noise can alter the characteristics of microphones at audible frequencies (be it dynamic, condenser, ribbon). Possibly through overcoming "static friction" or hysteresis effects that may be present, in mechanics or electronics.

Procedure:

Make a Control Recording:

Record a known sound through microphone in a controlled, quiet studio environment. Anechoic chamber would be best. For example, record a 10Khz sin tone playing through a speaker with fixed mic placement, and fixed recording chain Mic->Pre->A/D->harddrive chain.


Varient Recording:
Same exact as a above, but this time, have a second speaker in the room playing a high frequency noise. This noise could be white noise that is rolled off steeply with a highpass filter at around 30khz, such that no audible noise is emitted. Alternatively, one could have the high frequency emitting speaker play a 22Khz to 50kHz sin tone. The idea is to fill the room with additional high frequency noise, and see if it has any effect on the recording of lower, audible frequencies.


After recording the control and the variants, compare the noise levels, frequency responses, etc.

Alternatively, make just one recording. Have a blinded(not necessarily literally) assistant turn the ultrasonic frequencies on and off while recording.

There is a slim chance of this working, but if it does, it might just be worth the effort. It would be funny to see people plugging vermin repellent wall socket units in their tracking rooms. Also, if this feature worked, I could imagine microphone manufacturers including ultrasonic emitters in the bodies of microphones, drawing from phantom power.

I would do it myself, but my house is too noisey, and I don't have a tone generator to produce the ultrasonics (yet... just purchased on on eBay).