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Old March 2nd, 2007, 01:39 PM   #1
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Listening to the radio... When I don't want to...

I've had this happen twice to me lately, and would like to avoid it in the future if possible. Here are the specifics:

1. AT 897 boom on a boom pole pointed down at the talent
2. XLR cable connected to the bottom of the boom pole and into my XL2
3. XLR cable kept away from power cords and other cables, no other mics used

When I listen to the audio, one time I got a top 40 station coming through, and the other time I got a country station. The shoots were in two different buildings and at least a mile or more apart. But here's the kicker... on the second interview, the person I was interviewing had a Sennheiser shotgun available. So just to see if it would make a difference (about the RFI) we changed out the mics. Presto-Change-O, no RFI. I didn't change out the cable, move the cable, move the camera or anything. At the most I think I moved the boom arm up about two inches to compensate for the Sennheiser being a bit longer.

So here are my questions:

1. This doesn't happen all the time, but do you think my AT 897 is defective?
2. Hopefully it won't, but when I do pick up a radio station in the future, how do I get it out of the audio (Stop receiving it)?
3. What am I doing wrong?

Any help at all would be appreciated...

Thanks,
Kevin
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Old March 2nd, 2007, 06:42 PM   #2
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Kevin,
I had a Schoeps which would receive radio when I was near the Empire State Bldg. It was in my particular mic. Sounds like your AT 897 mic is not RF immune and you found the spot where it is vulnerable. If you can try and get a duplicate mic you are having trouble with and see if the problem is in the model/brand or just yours.
I am assuming you switched cables and took the boom cable out of the equation. Rarely I have had mic/cable combinations which caused troubles.
The only thing you did wrong is get stuck with only one mic to record with.
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Old March 2nd, 2007, 07:18 PM   #3
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Not Always the mic

I did a commercial shoot last November where I ran into the same problem...with three different microphones. I tried a Shure Lav, a Senheiser Shotgun, and an Azden Shotgun. I ran balanced sheilded cable and had no luck. I could even hear it through the headphones when the mic was not connected. turns out, I was less than a quater of a mile away from a broadcasting antenna. The signals were so strong that they were bleeding into everything...including phone lines.

Fortunately, I was able to lay down some music and mask it enough with some filters that it worked. There has got to be a way around it, though.

BRyon<><
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Old March 2nd, 2007, 07:41 PM   #4
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Here's a tip...

If you have 60 Hz hum bleeding into your mix (sorry, this only works for hum, not a radio station), sample the hum, turn it into a loop (cut it right at the zero crossings), invert it, line it up and listen to the hum go down to zero. It works even if the hum has lots of harmonics. Best of all, it doesn't alter the tone of the dialog the way that noise reduction can (especially if the harmonics are high).

The one place it doesn't work exactly right is when automatic gain control kicks in. If that's the case, use the canceling method above, then use a small amount of noise reduction to pull out the rest. It affects the tone of the dialog a bit, but not nearly so much as a full noise reduction approach.

Don't bother asking what drove us to come up with this solution. Let's just say it wasn't for the sake of theory!

Thankfully, our "studio" is in the hills far away from transmitters.
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Old March 3rd, 2007, 09:16 AM   #5
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Quote:
Originally Posted by Bryon Akerman View Post
I did a commercial shoot last November where I ran into the same problem...with three different microphones. I tried a Shure Lav, a Senheiser Shotgun, and an Azden Shotgun. I ran balanced sheilded cable and had no luck. I could even hear it through the headphones when the mic was not connected. turns out, I was less than a quater of a mile away from a broadcasting antenna. The signals were so strong that they were bleeding into everything...including phone lines.

Fortunately, I was able to lay down some music and mask it enough with some filters that it worked. There has got to be a way around it, though.

BRyon<><
In your case it was also being received in the recorder. It is very hard to properly shield a unit in the field.
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