Hi,

I'm trying to chase down the source of some 150,220,300 Hz
hums in my DV recordings. They sound like the camera
, but they're all not harmonics of 150. They're pretty
close to being harmonics of 75 Hz. Does anyone know
the motor speed of the miniDV cassette? BTW, I'm
using a Sony VX-2000 and notice this sound whenever
I use a microphone other than the internal. So, I'm
pretty sure the noise pollution source is the VX2k.

Also, I noticed a 51217 Hz sine wave in my AVI files using the
the SoundForge spectrum analyzer. I'm recording in 16-bit
mode, so the sampling frequency is 48000 Hz. Would anyone
know the source of this whine?

Thanks !

Vince, do you 4 times upsample your audio output? I'm just trying to figure out how you measure 51kHz component.

As for 75Hz harmonics, I have no idea. May be it's some aliasing? From switching supply regulators for example?
How audible this hum?

Ooops. That should be 15217 Hz.

Hello Vladimir,

I picked up the hum when using a stereo X-Y microphone
on top of the camcorder. I still have to restore those recordings,
but in the future, I'll move the microphone further away.
However, the hum will still be there, only at lower levels.
The mic can only be moved so far away, often at the expense of signal to noise ratio and a different directional sensitivity pattern.

Vince, microphone hum pickup is quite a common problem. I don't know exact reason, but there is a huge difference even between different samples of cameras of same model. This is really weird, as I think it should be no difference between similar cameras. Also, some microphones are more sensitive to the camera interference than others. Sometimes cables can make a difference.

I know, I did not answer on your question on noise origin. You can try to differentiate between mechanical or electrical coupling, if you place mic far away from camera on a wooden table. Then table would conduct an acoustical hum, while electrical hum should be minimized by distance. You can analyze the spectrum afterwards.