Picking Up Radio Signal on Sound Board RCA Cable

[Jason Robinson]

Originally Posted by Martin Pauly

No, I don't think so. As Seth pointed out earlier, you'd still be dealing with un unbalanced signal that is prone to picking up all sorts of noise, the more the longer the cable is that you use. If all you have is an unbalanced output (headphones, RCA, etc.), you can however run a SHORT cable to a balancing transformer, such as this one
http://www.rane.com/pdf/bb22dat.pdf
and run a balanced signal from there into your Beachtek, and that cable can be as long you need it to be. That would protect you much better from picking up noise.

Ok, so the fact that an XLR cable is used doesn't mean the signal is balanced. I would need a device to specifically create the balanced signal and send it over the XLR cable to the camera. So running a 1/4" headphone -> 1/8" cable to RCA splitter (L & R dedicated RCA) into the device you mentioned -> 20'x2 XLR cables -> XLR to something to step it down to 1/8" stereo mini jack into cam or a mono 1/8" mini jack into Beachtec.

Originally Posted by Martin Pauly

Well, keep trying. The basic ways to operate analog mixers are pretty similar between different makes and models of mixers. Typically, you have one AUX knob per input channel and per AUX output. The knob controls how much of that channel's signal is added to that AUX output. So as a starting point, plug your XLR cable into the mixer's AUX1 output, then adjust the kbobs labeled "AUX1" such that you open it a little bit for all channels you which to record, and close it completely for the other channels. That should give you something on your XLR cable. Then adjust the AUX levels from there.- Martin

about 1/2 thorough the event I found the Aux feed on the lapel input channel, but for some reason my AUX out via XLR direct to Beachtec (and monitored via headphones from the GL2 headphones out port) was not getting any audio. It is like there was some toggle on the mixing board that said "turn on this route" that I was missing because no amount of adjustments to the Mic1 Aux8 level could get the AUx8 line to register anything.

This leaves me wondering if I should be bringing my audio tech partner to all the events I shoot just so I don't need to mess with this in the future.

[Jason Robinson]

Originally Posted by Greg Boston

Since what you are picking up is an AM broadcast station, the late arrival of the traffic was likely due to sunset in the area that the signal originated from. AM stations have a problem in that their signals will travel great distances at sunset due to bouncing off the ionosphere. Therefore, they have three options... shut down at night, go to reduced power, or switch to a directional signal using a phased antenna array. All of this so that they don't interfere with other stations on the same frequency in other markets.
-gb-

Amazing. Now that I think back, it was right about sunset (started at 7pm went till 8:30ish). Huh. Basic HAM radio facts for the win.

[Ty Ford]

This leaves me wondering if I should be bringing my audio tech partner to all the events I shoot just so I don't need to mess with this in the future.[/QUOTE]

Ah! There's a good idea!

Regards,

Ty (audio tech) Ford

[Martin Pauly]

Originally Posted by Jason Robinson

Ok, so the fact that an XLR cable is used doesn't mean the signal is balanced. I would need a device to specifically create the balanced signal and send it over the XLR cable to the camera. So running a 1/4" headphone -> 1/8" cable to RCA splitter (L & R dedicated RCA) into the device you mentioned -> 20'x2 XLR cables -> XLR to something to step it down to 1/8" stereo mini jack into cam or a mono 1/8" mini jack into Beachtec.

Yes, that should give you a balanced signal for the long portion of your cable run.

about 1/2 thorough the event I found the Aux feed on the lapel input channel, but for some reason my AUX out via XLR direct to Beachtec (and monitored via headphones from the GL2 headphones out port) was not getting any audio. It is like there was some toggle on the mixing board that said "turn on this route" that I was missing because no amount of adjustments to the Mic1 Aux8 level could get the AUx8 line to register anything.

Another thing you can do is have XLR splitters available for each input channel, so that you can branch off all the relevant sources and feed them into your own mixer. Insert the splitter on the inputs into the house mixer. That should protect you from running into unexpected surprises with audio mixers that you don't fully understand.

This leaves me wondering if I should be bringing my audio tech partner to all the events I shoot just so I don't need to mess with this in the future.

You have an audio tech partner? Of course you should bring him or her along, whenever that is feasible! Having a person dedicated to audio is a significant improvement over doing video and audio all at once.

- Martin

[Jason Robinson]

Originally Posted by Martin Pauly

Yes, that should give you a balanced signal for the long portion of your cable run.

Great. I may have to try that. Another problem is I don't want to run a stereo signal because my on cam shotgun is using the left chan so I will need a mono signal from teh board. Considering that everything except CD music is mono, that wont' be a problem to just use one cable (also less expensive than buying another long XLR cable)

Originally Posted by Martin Pauly

Another thing you can do is have XLR splitters available for each input channel,

Ahh. a very interesting idea. I would need to know if the incoming XLR signal from the UHF receiver was mic level or line level. I suppose a Mic level signal cannot be split (or may be I'm wrong there).

Originally Posted by Martin Pauly

You have an audio tech partner? Of course you should bring him or her along, whenever that is feasible! Having a person dedicated to audio is a significant improvement over doing video and audio all at once.- Martin

Yes, but he is very expensive. I only use him for large events, or events with too tight of schedules for me to afford messing around with strange mixers. This event was very small, low margin, low profit. Given my need to pay December's mortgage, I'm trying to cut everything possible to keep treading water.

[Martin Pauly]

Originally Posted by Jason Robinson

I suppose a Mic level signal cannot be split (or may be I'm wrong there).

There are splitters for mic and for line level signals. With mic level, you just got to be careful with phantom power if the mixer provides that for the mic. Typically, there's an output labelled "direct" which should go the input of the device providing phantom power, and a second output that can go to another device.

- Martin

[Carl Hayes]

Everyone seems to be telling you what you did wrong and how to avoid it. No one is telling you how to fix it in post.

This is a common necessity in forensic work. You put a wire on someone to tape a clandestine meeting, and the meeting occurs in a very noisy bar, say, with a loud juke box. What you do is record another channel simultaneously, with just the juke box (maybe put a mike in front of the juke box. You might even wire another operative to tape this channel).


Now you have a recording of the audio you want, swamped by audio you don't want -- and a separate recording of the hated audio that did the swamping. There is software available to take the two files, subtract the unwanted-audio track from the desired audio track(s), and give you much cleaner audio. I could name one such program, but I don't want to get a rep for shilling someone's product excessively, even though I'm only their happy customer and haven't ever met them.

Swell, you say. I didn't do that. I don't have a tape of the radio station that I can have the software subtract. Ah, but maybe the radio station DOES have one. Or maybe you can record (in mono, I guess) the same "musical" selections the station played, and then at least get rid of the music, although you'd still have the DJ's voice in between selections (which might blend in with audience noise anyway).

The software versions that will do this forensic-type work for the cops will also do it for you. Unfortunately, it costs more than the non-forensic versions of the same software. How badly do you want to clean up your capture?

[Ty Ford]

Carl,

Have you actually done this yourself?

Regards,

Ty Ford

[Jason Robinson]

Originally Posted by Carl Hayes

The software versions that will do this forensic-type work for the cops will also do it for you. Unfortunately, it costs more than the non-forensic versions of the same software. How badly do you want to clean up your capture?

Not enough to bother paying for yet another software package. I have Soundforge & Vegas8pro. I've already cut it together and I will end up using the over the air shotgun audio or audio combined from the second cam (just an onboard cam).

This is a $300 gig, so nothing fancy.

I mainly wanted to know how to avoid this in the future with a hardware solution so I don't have to touch anything in post.

Though I would love to play with forensic level software!

[Greg Boston]

Originally Posted by Ty Ford

The clear channel stations (no connection to the company that eventually came to be called 'Clear Channel', were (are) 50 kW stations and mostly in big markets. They had the "right of way" , but even they go from omni to directional at night, mostly to not interfere with Canadian stations.

Your last sentence sort of bears out what i said. Directional, low power, or off air. For some stations, it's a combination of the first two.

I'm familiar with the 'clear channel' AM 50KW stations. I've got a bit of radio broadcast pedigree in my background. DJ, First Class license, ASET degree, yada, yada, yada.

-gb-

[Carl Hayes]

Originally Posted by Ty Ford

Carl,

Have you actually done this yourself?

Regards,

Ty Ford

Nope. I've read about it, and my cop friends (I have a lot of cop friends) assure me that (1) it's a standard approach for a well-equipped lab on big cases that warrant the investment of time, (2) they've heard and used the output, and (3) they were blown away. As an electrical engineer I know that the theory is sound.

I don't own the (forensic) versiion of Diamond Cut that includes this capability, though, and have never done it myself.

[Ty Ford]

Originally Posted by Greg Boston

\I've got a bit of radio broadcast pedigree in my background. DJ, First Class license, ASET degree, yada, yada, yada.
-gb-

right. me too. 1st phone commuted to a general, couple of CE gigs at stations.

Ty

[Ty Ford]

Originally Posted by Carl Hayes

Nope. I've read about it, and my cop friends (I have a lot of cop friends) assure me that (1) it's a standard approach for a well-equipped lab on big cases that warrant the investment of time, (2) they've heard and used the output, and (3) they were blown away. As an electrical engineer I know that the theory is sound.

I don't own the (forensic) versiion of Diamond Cut that includes this capability, though, and have never done it myself.

Well sure the theory is sound, but theory and practice seldom agree. In this case,
{You said: You put a wire on someone to tape a clandestine meeting, and the meeting occurs in a very noisy bar, say, with a loud juke box. What you do is record another channel simultaneously, with just the juke box (maybe put a mike in front of the juke box. You might even wire another operative to tape this channel).}

If the two mics are different distances from the jukebox, the time delay will have to be compensated for for cancellation. In this scenario the room acoustics and system differences will mess with the two signals enough to make cancellation difficult at best.

Yes, the forensic guys have nice toys, but a lot of the CSI stuff you see on TV is still fiction. It's not likely that you'd be able to create an mirrored radio station interference signal to null the stuff on the tape you don't want. And the forensic guys aren't really concerned about fidelity, they just want to be able to hear what was said. That's different from trying to reclaim audio with any fidelity.

Regards,

Ty

[Jason Robinson]

Originally Posted by Ty Ford

That's different from trying to reclaim audio with any fidelity.
Regards,
Ty

Right, which is why I am much more interested in correcting the problem at the source and getting a hardware solution. As much as I like my work, I hate the wasted time in Post to fix these annoying but devastating errors.

[Ty Ford]

Jason,

right. Do I remember correctly, you heard the AM during recording? I'm asking because some folks have said they recorded and didn't hear anything until playback.

That either meant maybe they weren't hearing it during record and it was there, or somehow it got in later. Like maybe during transfer.

Balanced audio is the best defense against RF. IIR, you have unbalanced audio inputs and a collection of unbalanced adapters to get to the camera. That in itself could do it. Although sometimes, it still gets into balanced audio as well.

You're best defense is having a variety of solid front end gear and a stash of different gozinta and gozouta cables. Your audio guy should have them. I don't know what you currently use as a mixer, but a Sound Devices 302 mixer can cure a lot of these problems with its balanced transformer inputs. They help to scrape off the bad audio problems before they get to the camera.

For your mixer to camera cable (if your camera has a stereo 1/8" unbalanced stereo input) I'd get a regular "balanced mixer to camera with headphone return" cable. The camera ends will be male XLRs. Get two short female XLR to male RCA cables and a Y-cable with two mono female RCAs on one end and a male unbalanced 1/8" stereo TRS plug on the other.

Regards,

Ty Ford