Comments on: We're going to air, please turn down your radio

Question: We're going to air, please turn down your radio

tellurian — Wed, 08 Feb 2006 14:52:21 -0800

Phoning a live radio show while you have your radio on causes some problems. I was listening to a radio station this morning and three people had phoned in to be part of a competition. One of the callers had their radio on and it caused the most unholy squealing feedback giving the presenters conniptions.
Can anyone explain to me in layman's terms what's happening here? What configuration has to be in place for this to occur? Other answers I'd like - How close to the radio does your phone have to be (or is it the volume)? Do you or the station have to be making a sound before the feedback happens? Do you have to be tuned to same radio station or is it just the fact the you have the radio on?

By: Kellydamnit

Kellydamnit — Wed, 08 Feb 2006 14:57:30 -0800

I think part of the problem is that any (US) radio show that takes callers is, by FCC regulation, broadcasting on a delay (7 seconds, iirc). So if the radio is on you'll actually be hearing over the phone what was broadcast a few seconds ago.

I don't think that can explain the squealing, though.

By: Who_Am_I

Who_Am_I — Wed, 08 Feb 2006 14:58:43 -0800

I think this is a feedback loop, caused by the delay that the radio station has in place.

By: rc55

rc55 — Wed, 08 Feb 2006 14:59:02 -0800

It's basically a feedback loop - the sound output is accumulating because the radio is amplifying the phone call, and the phone's microphone is sending the same signal back to the radio station, which in turn is causing the same cycle to repeat itself.

With every "loop", amplification is accumulated and as such the residual audio signal is combined and amplified resulting in the feedback noise.

As a brief aside, it's quite an interesting thing to observe by putting your microphone next to a speaker on a Skype call, as the latency makes the accumulation slower, but you can hear it happening for real - but make sure your speakers are turned down quite low, feedback always drives speakers very hard.

By: commander_cool

commander_cool — Wed, 08 Feb 2006 15:02:19 -0800

If there was a tape delay, there wouldn't be feedback, just a distracting lag that would confuse the caller. It's the fact that the radio is on to the same station, broadcasting live. The mouthpiece of the phone is picking up noise from the radio, the radio rebroadcasts the noise that the phone is picking up, the phone picks it up, etc., getting louder with each iteration -- hence the term "feedback." It's the same effect as putting a live microphone in front of a speaker in a cheap sound system.

By: jessamyn

jessamyn — Wed, 08 Feb 2006 15:02:28 -0800

And in answer to your other questions, this happens when you are tuned to the same station that your voice is being broadcast over and your radio is loud enough to be audible through your telephone; distance doesn't matter, decibels matter. I used to screen calls for public radio in Seattle and one of the things we would always tell people is "turn your radio down NOW, if you wind up going on the air, it will be bad if your radio is on loudly"

By: smackfu

smackfu — Wed, 08 Feb 2006 15:08:27 -0800

Besides any possible censorship delay, I'm sure there's some unavoidable delay just in the system of phone to radio station to antenna back to your radio.

By: kindall

kindall — Wed, 08 Feb 2006 17:19:00 -0800

There is now, especially with cell phones and VOIP, but there used to be a lot less, especially when callers are in the same city, which would be the case for a radio station. It was all analog in those days and it's hard to slow down electricity.

By: holloway

holloway — Wed, 08 Feb 2006 18:03:53 -0800

Acoustic Engineers... Is there any chance of software detecting these loop patterns and reducing them?

By: Roger Dodger

Roger Dodger — Wed, 08 Feb 2006 18:38:54 -0800

There are feedback exterminators that will target narrow bands of frequencies that are causing feedback, and bring the gain down for that small area of the spectrum. I don't think that they would be useful in this situation, though, as the telephone really cuts down on the bandwidth that you are using, so there is only a small selection of frequencies feeding back to begin with.

By: meehawl

meehawl — Wed, 08 Feb 2006 19:59:32 -0800

The original 1963 Doctor Who credits were made using visual feedback, basically pointing a camera into a TV monitor, randomly flashing pulses of light, then recording the results. So you're basically watching a visual analogue of the feedback screech. Apparently they got the idea from a 1951 TV show.

By: intermod

intermod — Wed, 08 Feb 2006 20:12:06 -0800

Just to be crystal clear, tape delay has nothing to do with the howling feedback, in fact it tends to suppress it. Even a tiny bit of delay (e.g. in a cell call or VoIP call) might be enough to mitigate it, although you can hear it trying in the background.

By extension, if the feedback takes the form of the unholy howl, then the radio station is probably NOT using any tape delay, thus practicing unsafe talk radio, and you should call into and swear your fucking head off. Shut up, Beavis.