Broadcasting w/o Audio Processing?

[Kelly A]

If the above sounds interesting to you and you'd like to try it out, everything I wrote above is ancient history, no one would use this technique today. It is embarrassing that it was done this way, things are so much better now.

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Well said. In the dark ages when I started fooling with audio processing and modulation control; I modified the crap out of a Gates Solid Statesman, mainly because I became frustrated with the pumping and peak overshoots of a Volumax. Many of those memory cells are long gone, but believe I decreased the attack and increased release times of the first stage limiter, disabled the 'gate', and drove that at a much higher threshold. I also modified the clipper circuit, creating a more defined ceiling. I then drove the Solid Statesman with an Audimax as an AGC, and a parametric EQ sandwiched in between the two. End result was reasonable peak control without any noticeable pumping or breathing. The trick was to not overdrive the Solid Statesman clipper more than about 6dB of clipping. You're right though, hit over 10dB of clipping, and things get pretty messy.

 

[comanchero]

1) OK, so what happens if one (intentionally) undermodulates?
2) How about Stereo Tool? 💻

 

[Kelly A]

1) OK, so what happens if one (intentionally) undermodulates?

Other than competitive reasons, there is no problem with under-modulation. Certainly as it relates to FM.

 

[comanchero]

Other than competitive reasons, there is no problem with under-modulation. Certainly as it relates to FM.

So will the station be quieter? If so, by how much - is there a formula to calculate (kHz = dB)?

 

[Kelly A]

So will the station be quieter? If so, by how much - is there a formula to calculate (kHz = dB)?

It's just audio level. The frequency of the station has nothing to do with audio level. If you modulate an FM station with a 400hz sine wave tone at say 25% modulation, that would be the equivalent for received audio level of roughly -35dB. There's also the 'uncalibrated knob factor' which includes a volume control on the end user's receiver.

 

[kevtronics]

I then drove the Solid Statesman with an Audimax as an AGC, and a parametric EQ sandwiched in between the two. End result was reasonable peak control without any noticeable pumping or breathing. The trick was to not overdrive the Solid Statesman clipper more than about 6dB of clipping. You're right though, hit over 10dB of clipping, and things get pretty messy.

About 20 years ago I used a Solid Statesman FM limiter with a CRL Spectral Energy Compressor ahead of it. With the CRL carrying most of the weight, it really wasn't that bad. IIRC I had the "Clip Above" set to 4 kHz.

http://www.amstereo.org/files/crlgatesfm.mp3

 

[dc2bluelight]

Pity DE isn't pilot-activated - then we could just avoid the whole crippling thing. 😥 (I know you get more noise w/o, but modern NCO DDS TXs achieve SNR as high as 90+ dB, so who cares?)

It's not a transmitter noise problem, it's a reception problem. We've had close to 90dB TX s/n for almost 40 years. Nice, but it doesn't solve the problem with received noise. The quietest receiver I ever tested was only in the mid to high 80s, and that went away when you put an actual antenna on it. Now make it mobile, throw in some multipath, and it turns out you do need that pre-emphasis after all.

TVs and AVRs have their "night modes" for that, right? So why worrying about implementing it at the TX site? The EU (ITU?) regulates the commercials loudness, as their authors intentionally make 'em as loud as possible; thus the broadcasters simply reduce all of them by 3 (or 6?) dB, I guess - or maybe some of them process them in a more sophisticated way.

The "night modes" aren't standardized. Every manufacturer has their own ideas. However...an idea I tried to suggest during the IBOC decision days...rather than transmit pre-processed audio, transmit a low-bit-rate control stream that included directions to default radios to what the station desired, but offer listener options to reduce or eliminate processing at the receiver. Sort of a "rosetta stone" bit stream. But nobody cared, so...we got what we got. Also cheap DSP wasn't quite ready yet.

Well, it seems that the advocates of the DAB/DAB+ may be right - IF you utilize its possibilities to the max, it probably may sound better than the FM; despite the lossy AAC+ codec. But then, you pay pretty much for the MPX capacity, so you don't save much (if at all) on the "digital advantage".

From what I've heard, it's only better in some ways, worse in others. Getting better as codes improve, where FM is kind of stuck where it's been. As the DAB advantage...well, FM is being shut off in some places where DAB is the norm, so no choice.

 

[dc2bluelight]

About 20 years ago I used a Solid Statesman FM limiter with a CRL Spectral Energy Compressor ahead of it. With the CRL carrying most of the weight, it really wasn't that bad. IIRC I had the "Clip Above" set to 4 kHz.

http://www.amstereo.org/files/crlgatesfm.mp3

About 47 years ago I replaced a set of Gates Solidstatesman FM limiters and the matching AGCs with an Optimod 8000. It was like someone blew the roof off the station and wired the transmitter directly to your ears. The difference was unbelievable. And 8000s weren't any great shakes by later standards!

Those Gates things, used as designed, were hardly worth the tin they were stamped out of. Unless that's all you had, of course.