Hum in audio

CVM wrote on 2/13/2011, 9:14 AM

I have the Sony AX-2000 video camera and the Azden SGM 1X shotgun microphone. Granted, it's not the most expensive mic out there, and it has been giving me some problems:

1.) LOW VOLUME. If I leave the camera audio on automatic, the mic level is too low. I need to switch to manual and pot it up. I can also go into the audio settings and pump up the gain. However, doing these things causes my second problem:

2.) HUM IN THE AUDIO. While generally not a problem in noisy recordings, in quiet recordings it is horrible. There is only one adjustment on the mic, high-pass filter on/off, but that doesn't fix it. I don't know if it is a 60Hz hum or what.

3.) HERE'S THE BIG QUESTION: HOW CAN I FIX THE AUDIO I'VE RECORDED? I shot a stage performance, and the hum is acceptable to general audiences, but it grates on my nerves. There are SO MANY settings and plugins I've tried, but I have no clue what I'm doing. I just want the hum to go away. I downloaded Sony Noise Reduction as a trial and found out it doesn't work on 64-bit Vegas 10. What the hell?? I've reviewed posts on how to try to eliminate the hum, but it changes it, doesn't get rid of it or reduce it significantly.

So, my Vegas friends... I realize there are many things I can do to improve audio capture in the field (better mic, tap into the line feed, etc.) but what would you do to fix my audio hum without buying expensive audio sweetners?

Thanks.

Dave

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Comments

CVM wrote on 2/15/2011, 6:49 PM

Holy mackeral, everyone! I am simply amazed at the time, energy, and effort you have put into my issue! Thank you all very much. I am very impressed at how some of you were able to fix the audio... even the coughs!

Everytime I think I know what I'm doing, I discover I have a long way to go. Granted, this is a part-time gig for me (even with the new AX-2000) but I always want to produce a quality product.

Funny thing is... I recorded the shotgun on channel 2 on manual (to bring up the volume since that Azden really has low levels for some reason - it even was low on my GL-2)... and recorded the camera mic on channel 1 as a back-up because I heard the shotgun hum in my headphones before the show. The camera mic (while VERY hot) did not have much hum at all. Yeah, it did pick up children picking their nose in the audience, but the audio was just crisper. I thought the shotgun using a six inch XLR cable would have been superior. Maybe it is and I just dont' know how to properly set it up.

Anyway, thanks SO MUCH for all your help and insights. You guys NEVER fail to help!!!!!

Dave

johnmeyer wrote on 2/15/2011, 8:35 PM

You should not be getting "low levels" with this microphone. I just checked the manuals for both the mic and the camera. On the mic, you obviously have to turn it on, which I assume you must have done or I don't think you'd get any audio. However, as others have already pointed out, you should test your battery and make sure you are getting 1.5V.

On the camera, it appears that you have more input settings to choose from than I do on my Sony FX-1. Here's what it says in the manual:Set the INPUT1 switch B to an appropriate position for the microphone
connected to the INPUT1 jack A.

LINE: For inputting sound from an audio device

MIC: For inputting sound from an external microphone that does not support the +48V power source.

MIC+48V:For inputting sound from a device that supports the +48V power source.

When you connect a microphone to the INPUT2 jack, set the INPUT2 switch to an appropriate position for that microphone.
So, this switch obviously must be set correctly.

craftech wrote on 2/16/2011, 2:58 AM

CVM,

Were do you have your TRIM level for the external microphone set? According to your manual:

If it is set too far to the minus side, the microphone volume becomes too low, resulting in a poor signal to noise ratio..

John

amendegw wrote on 2/16/2011, 4:54 AM

Ha! I just realized I have this exact same mic (in a box in my closet). So I got it out and ran a test here: AzdenSGM1x.wav While it was not recorded in a studio and the mic is not "A" quality (as musicvid would suggest), I don't hear the problems in CVM's video clip. I'd like to hear other's opinions.

I would suggest that this eliminates the hypothesis that these problems are inherent to this make/model of mic.

...Jerry

farss wrote on 2/16/2011, 5:20 AM

"I would suggest that this eliminates the hypothesis that these problems are inherent to this make/model of mic"

Not at all. If the mic has poor shielding then depending on the environment it may or may not exhibit problems with RFI or EMI. If I recall correctly the body of the mic is made of plastic, not a material reknown for it's good shielding properties.

Bob.

craftech wrote on 2/16/2011, 6:12 AM

But as I mentioned above Bob, the reviews I searched out (both User Reviews and Pro Reviews) don't suggest design flaws nor the problems CVM described. That would lead one to narrow down the problems to the camera settings, the interface, or the cabling.

John

musicvid10 wrote on 2/16/2011, 6:42 AM

Jerry, the real problem with that particular recording is detailed eleven posts up (after I analyzed the sample).

In short:
1) Record levels too hot
2) Peaks hitting limiter, raising noise floor and reducing S/N to <30dB
3) Limiter starts letting go at beginning of selection; and as a result,
4) Hum and noise steadily crescendos over 9 seconds to quite loud levels

My earlier footnote about the mic brand is secondary to that problem, which is with the recording itself. Personally, I think shotguns are noisy, and Azden is no exception. In that sense, Bob's point is well taken. Put any mic in the same room with stage dimmers, and the game changes completely.

I will note that your sample is not clipped, and the dynamic range is >=40dB, which is typical of a mid-line shotgun in real-world recording. Entirely different than the OP's sample. If I was to put on a limiter and raised the level by 12dBFS, yours would be just as noisy (but with less hum) ;?)

amendegw wrote on 2/16/2011, 10:20 AM

"If I recall correctly the body of the mic is made of plastic, not a material reknown for it's good shielding properties."The barrel is definitely made of metal. It's not magnetic so I suspect aluminum. At least that's what it looks like when I unscrew the battery the tube revealing the battery compartment - maybe magnesium alloy? Of course, it still could have a problem with electro-magnetic shielding.

...Jerry

paul_w wrote on 2/16/2011, 10:32 AM

Jerry,
Could you possibly do a test here, with a test meter, is the metal body electrically connected to pin 1 of the XLR connector? test between body (exposed bare metal, not paint) and pin1
This will confirm shielding.
Paul

amendegw wrote on 2/16/2011, 10:54 AM

"Could you possibly do a test here, with a test meter, is the metal body electrically connected to pin 1 of the XLR connector? test between body (exposed bare metal, not paint) and pin1"Confirmed; I got continuity between pin 1 and a metal screw on the barrel as well as the screen mesh covering the holes in the barrel.

...Jerry

PS: Not knowing which pin was #1, I tested all three and confirmed the result by Googling "XLR Pinout" when I got back to my laptop.

paul_w wrote on 2/16/2011, 11:14 AM

Nice one Jerry.
Guys, take it from me, this mic is shielded. Of course there are various levels of EM shielding, but at the frequencies we are talking about here (ie just audio) this is about all we need to know.
There seems to be a drive here for over-complication! please read my 'Gain' post earlier. This is simply bad mic placement - resulting in the OP cranking up the gain way too high to get any signal - result - Hiss and Hum. (now i am repeating myself!!).
Call it S/N ratio (signal to noise) call it semiconductor electron F noise.... etc... Thats all the complicated words... same thing really - Hiss (and a little bit of hum) by too much Gain.

Paul.

PS, can i just add that i am assuming the OP HAS tested his battery, AND XLR leads are wired correctly. That has to be done first.

John_Cline wrote on 2/16/2011, 1:43 PM

musicvid10 wrote on 2/16/2011, 8:06 PM

"(now i am repeating myself!!)"

Paul,
I too, am feeling a bit invisible here, after having stated exactly the same thing three times.
The issue, as we both have identified, is as visible as the nose on one's face.

craftech wrote on 2/17/2011, 3:57 AM

For those of you that just can't justify spending the $349 for Izotope RX2 maybe you could consider spending $40 for Izotope's "Music and Speech Cleaner." I suspect it works really well.

Link.
=================================
Thanks John. Very reasonably priced. I have the Sony NR plugin so I probably wouldn't opt for it as it requires separate processing and re-importing back into Vegas, but for those who don't have NR software, I looked for some reviews.

Macworld reviewed it for use with podcast files. They seemed to like it except that the 45 minute 256 MB file they processed into a new .wav file ended up 1.48 GB. Probably not an issue for most of us, but maybe?

Macfeed reviewed it and compared it to the $750 Adobe Sound Booth. They didn't like it at all and said that the Adobe Sound Booth software was "easier to use" ??? Not a very specific review though.

Amazon User Reviews were generally positive, but there were only five of them. One person pointed out something the "professional" reviews seemed to miss completely and a limitation that in my opinion makes this a really bad choice. You cannot apply NR to a small segment of the audio. You have to apply it to the entire audio file. That's OK if the whole track is bad, but what if it's only a section or a passage. You would have to work around it by isolating the bad section in Vegas yourself , separating the section, processing that in Speech Cleaner, then re-inserting it back into the Vegas timeline. No Thanks.

Another option, although a bit more complicated to learn, that works well and is free is Audacity.

Here is the Wiki on how to do it.

John

paul_w wrote on 2/17/2011, 8:54 AM

Well, i can see you musicvid ! System is working.
I think having spelt out the cause of the problem its time for me back out. Good luck to the OP. Hope you get this resolved for future projects.
Glad to help out.

Paul.