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25hz & 35hz subaudible tones..?

S

spinjector

There's something I'd like to do with good old-fashioned 25hz & 35hz sub-audible tones & detectors.

But...can anyone tell me...is an analog FM signal capable of successfully passing 25hz & 35hz...?

Thanks.
 
How noticeable would it be on an average car stereo, on analog FM? Would it rumble a lot? It's been since the dawn of my career 20 years ago since I've worked with it, and I can't remember. I figure the HD would be much more likely of having it audible.
 
Why would HD make it more audible? If your audio processing will pass 25Hz (and some will not) the analog transmitter should have no problem.
Actually, the digital compression of the HD audio might have a problem passing these low frequency sine waves.
Whatever ... keep the level of the 25Hz/35Hz at least 10dB below the program audio level to keep the tones from causing your program audio to 'duck'.
 
I'm curious what the OP is wanting to do with the tones?

R
 
This is for something I want to do with our audio logger, to save people time, especially in the traffic department...and it would be easier if not for the HD & profanity delays. We have Nexgen for automation, which provides a little-known relay output that closes when a spot block plays. And we have iMediaLogger for logging, which can record any given audio input in up to four different ways, and stop/start any recording on relay inputs. So I want to use all of this together, with the 25hz & 35hz tones playing operator in the middle, passing along through the audio delays, to trigger the recordings when blocks play.

The recordings would go into the network share with all our logger files, in a folder called "...\Spot Blocks Only". The reason for all this business with the tones & delays is so the recordings are pulled from the off-air tuners, so the traffic people don't have to waste time fast-forwarding and rewinding through 15-minute logger files for hours per day. If my idea works, all they'd have to do is go to a folder and look for a few perfectly encapsulated recordings per hour - and because they were recorded off-air, they'll know if the spots aired correctly or not.

Later on down the line I also want to make use of the Nexgen voice-track relay, and the console mic tally, to do good old-fashioned air-check recordings too.
 
Theoretically, you can do what you're suggesting. A couple of possible snags to look at though... I've never had one of these, but some exciters were said to be finicky about really low frequencies. The audio input was filtered, to drop everything under about 50 hz to prevent the PLL from unlocking and shutting the RF down. You'd need to check that with your system.

2. You're going to want to set the tone level to a LOT lower than -10. Fact is, I doubt you'll find a working level that someone won't hear. If you're going to tone-in and tone-out your breaks, and possible also when you mic in and out, it might get irritating quickly. One or two complaints from a listener with subwoofers and your project is likely to get pulled.

Most 25/35 setups assume you DON'T want to broadcast the tones, so the encoded audio is passed through a filter in the decoder... which usually is at the audio output of a satellite recever, or the like. In your case, you'll need to filter your station audio before the ENcoder, so nothing travels down far enough to false-trigger your setup. This means you're going to be filtering all of your station's audio, just so you can provide a clean band for your tones. That might matter... or not. Just so you know.
 
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Yea the issue with the subwoofers is why I question if it'll work without being annoying. But the tone levels wouldn't have to be high; the RF signal strength going into our off-air monitoring system is strong, and this is only for our ears.
 
Should be interesting then. One thing that'll make this more challenging will be your processing system. That's going to make the level of your tones variable, and maybe hard to calibrate your decoder to. That's assuming, as has been noted earlier, that the processor will accept them at all.

Creatively, if you're running a composite STL, I wonder if a subaudible could be injected into the subcarrier input. If you're running audio into the exciter, you might be able to bridge the processor output with the output of the encoder. Either of these might get you around feeding the audio through the processor, but I can imagine a number of unwanted side effects.
 
Interesting idea, but I wonder if there isn't another way to do this without tones. Couldn't you configure the automation system to trip a relay when specific elements start / end, and have that relay tell another computer to record the audio that is fed to it via a receiver?

R
 
I don't think adding to the composite would work, because the tones have to pass through all the delay lines with the audio, that being the HD and profanity delays. One might argue that I could simply delay the trigger relay, but that wouldn't work because the delay would vary depending if the profanity delay was entering or exiting. Also I wouldn't want to fiddle directly with the composite for risk of introducing some kind of unwanted junk there that might cause weird trouble somewhere else.

One thing that might work in favor so the processing wouldn't sit on the tone, is that most spots won't have crazy bass at the beginning, and as long as the tone level is higher than the expander threshold, it should be ok.

I guess the only way we'll all know is once I try and see how bad it goes. =-)
 
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