miniDV tape frequency ? at DVinfo.net

Go Back   DV Info Net > The Tools of DV and HD Production > All Things Audio

All Things Audio
Everything Audio, from acquisition to postproduction.


Reply
 
Thread Tools Search this Thread
Old June 19th, 2003, 07:26 PM   #1
Regular Crew
 
Join Date: Jun 2003
Location: Santa Clara, CA
Posts: 33
miniDV tape frequency ?

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.
Vince Denali is offline   Reply With Quote
Old June 19th, 2003, 07:28 PM   #2
Regular Crew
 
Join Date: Jun 2003
Location: Santa Clara, CA
Posts: 33
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 Denali is offline   Reply With Quote
Old June 20th, 2003, 02:28 AM   #3
Regular Crew
 
Join Date: May 2003
Location: Israel
Posts: 115
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?
Vladimir Koifman is offline   Reply With Quote
Old June 20th, 2003, 12:45 PM   #4
Regular Crew
 
Join Date: Jun 2003
Location: Santa Clara, CA
Posts: 33
Ooops. That should be 15217 Hz.
Vince Denali is offline   Reply With Quote
Old June 20th, 2003, 12:48 PM   #5
Regular Crew
 
Join Date: Jun 2003
Location: Santa Clara, CA
Posts: 33
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 Denali is offline   Reply With Quote
Old June 20th, 2003, 02:25 PM   #6
Regular Crew
 
Join Date: May 2003
Location: Israel
Posts: 115
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.
Vladimir Koifman is offline   Reply
Reply

DV Info Net refers all where-to-buy and where-to-rent questions exclusively to these trusted full line dealers and rental houses...

Professional Video
(800) 833-4801
Portland, OR

B&H Photo Video
(866) 521-7381
New York, NY

Z.G.C.
(973) 335-4460
Mountain Lakes, NJ

Abel Cine Tech
(888) 700-4416
N.Y. NY & L.A. CA

Precision Camera
(800) 677-1023
Austin, TX

DV Info Net also encourages you to support local businesses and buy from an authorized dealer in your neighborhood.
  You are here: DV Info Net > The Tools of DV and HD Production > All Things Audio

Thread Tools Search this Thread
Search this Thread:

Advanced Search

 



Google
 

All times are GMT -6. The time now is 12:08 AM.


DV Info Net -- Real Names, Real People, Real Info!
1998-2017 The Digital Video Information Network