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Old March 7th, 2005, 11:02 PM   #1
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Audio hummm question for pd 150

OK -- so after reading these boards for months -- I finally took the plunge and bought a used pd 150 for what I thought would be a bargain price. The serial number is 1015821 -- which I think is the "after the hiss problem was solved". Anyhow, I am getting a noticeable low audio hum when I listen to the audio (through my headset) -- I do not know if this is the same thing as the hiss or not.

Also, the hum is so loud, when I press the audio level button to check the sound levels -- even when the camera is recording in a silent room -- I get "two bars" rather than 1. That is to say, instead of the getting a single bar under negative infinity, I get two bars (I guess that would put it at -38 decibels rather than negative infinity).

I am using the original microphone that came with the pd 150.

I am operating in Agc mode. Input level is mic. Using + 48v on input 1. Going into input 1. Doesn't matter if I record to Channel 1 or Channel 1 plus Channel 2.

Here is something important: when the camera is on STANDBY or actually recording (and the tape mechanism is engaged) the hum sound is present. However, when the camera exits STANDBY (and I think the tape mechanism disengages) the hhum sound pretty much disappears -- the audio level bars (in a silent room) return to one bar from two bars -- (although to be honest, it still sounds kind of "large cave" windy).

Here are some other things:
if I put the "wind" option to "on" the humming/windy sound diminishes significantly -- and the audio level bars return to one bar from two bars. (Mind you, this is inside, when there's no wind present)

Also, if I choose the menu option of "MIC NR" on -- the humming sound diminishes -- although this might not be ultimately a good decision because of interference with dialogue (Alanbarker.com).

Finally, and this is kind of weird, but when I press the base of the microphone (where the standard Sony shotgun microphone wire leaves on its way to the xlr) I can make the humming sound louder but only when the tape mechanism is engaged (i.e., in standby or record mode).

Are all of the pd 150's this way? Is this something that I just have to live with?

Anybody with any experience with this -- please help! Thanks!

Albert Wong
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Old March 7th, 2005, 11:40 PM   #2
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Sounds like a tape transport noise issue. Whether it is normal or not is hard to tell. The microphone mounted on the camera will pick up the transport noise. That's what the NR is for but then, again, one shouldn't normally use the microphone mounted on the camera for careful work.

I'd bet if you moved the microphone off-camera, the problem would disappear.
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Old March 8th, 2005, 12:32 AM   #3
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You are exactly right! :-)

Mike, You are exactly right! :-) I think that it must be (at least in part) a tape transport sound issue. I could actually hear the tape transport "winding down" as it moved from Standby to "off" mode.

Just like you suggested, I just tried moving the microphone off-camera -- and like magic -- the humming sound disappeared! Amazing. Thank you, Mike! :-) I thought that I had tried that -- but I guess I just was not listening right.

The bad news is, that even without the tape transport hum sound mucking about, there is still some other hiss-type sound that is left-over -- but that may be just the unavoidable ground level system noise. :-( (It seems to fit the sound profile for system noise that Alan Barker talks about on his web site.) I guess I will just have to make sure that when I record sound, everything else is loud enough (like the -12 decibel level) to make the system noise (at least by comparison) negligible.

It just seems like I am going to have to record my subjects from less than four feet away (if I want to get -12 decibel range -- at least with the microphone that came with the pd 150). Thank God there are wide angle adapters! :-)


And thank God for this user group :-).

Cheers, Albert
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Old March 20th, 2005, 01:48 PM   #4
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Okay -- this is kind of connected to this thread -- along the lines of "the unending Albert Wong sound saga" -- but I finally got around to capturing some of the footage of the pd 150 into final cut pro -- and it turns out that even when I am recording in a "quiet room" -- without the tape transport noise problem (which has been solved from above), there is some base-level hiss-sounding noise -- it shows up at a ground floor around -50 decibels on the final cut pro audio levels bar after I capture.

Is that -50 decibels ground floor noise normal?

In the end, this might not be a big deal, especially in a busy real world situation where there is lots of background noise. But in a quiet interview situation where there is a lot of silence, I'm a little bit worried that the -50 decibels hiss sound is going to be distracting to people listening.

(As I mentioned earlier above, the serial number indicates that this is a post-hiss pd 150 -- and I am using AGC -- and the stock microphone.)

Am I being paranoid about the sound?

Thanks! :-)

Albert
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Old March 20th, 2005, 06:07 PM   #5
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That sounds about right. The 150 isn't really quiet like my DSR-300 or a stand-alone good quality sound recorder. But then I almost never have any of my work dead quiet in the background since I tend to not work in studios.
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Old March 20th, 2005, 07:06 PM   #6
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Thanks for the lowdown, Mike -- appreciate it!
:-)

I think it should be fine -- at least for my purposes. I'm not going to open nationwide anytime soon :-)

Regards,
Albert
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