DVX100B & AT835ST: noise @ 150Hz
 

I have the DVX100BE (PAL) and a Audio Technica AT835ST (Stereo / M&S XLR 48V) mounted in the camera mic holder, and I have noticed terrible low-level noise in all videos. Finally, when I switched to Vegas, I was able to isolate the noise to 150Hz @ -30db , so I have cut this frequency out and the sound is now excellent.

Is this a new problem, or a known issue with the DVX100B (maybe the PAL version?), or the mic? It is on both L and R (I dont use M&S functionality), Narrow setting, and "normal" camera level settings. I may have to try the mic at Wide settings, and with the 80Hz roll-off filter off, if this is not a camera issue... unless that is the inherent noise of the tape drive in the DVX100?

Thanks

Chris,

Is your camera running off batteries or outlet power? Outlet power can often introduce those types of noise.

Josh

No, the camera is running on batteries.

After comparing with video before I got the AT835ST, using the built-in mic, I understand that the 150Hz noise was always there, but with the built-in mic there is so much other noise that cancelling out 150Hz is not enough to reduce the noise floor: the whole frequency spectrum is full of noise, some camera handling and tape drive noise, but I suspect more than that too.

With the AT835ST, the noise is completely reduced at all frequencies, and the 150Hz noise becomes noticeable even though it is not louder than with the built-in mic... removing 150Hz brings the noise floor right down to barely noticeable, without applying any other audio correction. What is strange is that other camera noise, like the zoom motor, is not noticeable with the AT835ST... could this 150Hz noise be in the electronics (and not a mechanical noise)?

I wonder if 150Hz is 3x 50Hz PAL noise, and in NTSC land the noise is @ 3x60= 180Hz? I didn't experiment with the shutter at different speeds, but maybe there is more to it than that?

What is the typical technique people use to reduce the noise floor in scenes with low volumes? The Dynamic Curve (like Vegas Gaphic Dynamics) (similar to a gamma curve for audio) seems like a good way to reduce the low-level noise and maintain appropriate dynamic range for the rest?

Thoughts appreciated.