Hi
There's more nonsense talked about audio processing than there is about almost anything else.
You need a compressor - a variable ratio up to about 4:1 is good. A variable threshold is also good, but not essential - you can adjust the incoming level for that. A limiter is also essential, but TBH, you're probably not going to do much better than an op-amp with sime diode clippers in the feedback loop.
To do broadcast limiting properly, you need a "feedforward" circuit, that uses a delay line to eliminate the "attack" time of the limiter and prevent overshoots. Conventional limiters (unless they're clippers) can't do this - no matter what Orban claims! Delay-line limiters tend to be more expensive, but I'll provide a relatively cheap, high performance circuit to this website in the next few days.
Contrary to what you've been told elsewhere in this thread, an expander is actually useful. You can use it as a low-level detector circuit to prevent the compressor amplifying low-level noise! Effectively it's used as a noise gate. Most programming won't ever be affected by it, and it's certainly not essential.
If you're prepared to get a soldering iron out and do a little shopping (NOT in the USA - you'll want to buy your parts from Futurlec or Tayda to reduce your costs by about 80%), you can build yourself a superb-sounding audio processor that'll make your station sound much better than the competition.
Don't use agressive compression, and don't hit the limiter too hard. Use the correct pre-emphasis and allow your listeners to adjust their own tone settings to suit themselves - don't force your preference on them, just broadcast a flat response (with pre-emph of course). Your audience will thank you for it! you'll also find it less aurally fatiguing as well, meaning that they'll listen longer......
I am sorry but some of your suggestions regarding processing are not correct.
For instance a feedack limiter with 1ms attack time followed by a clipper works just fine , distortion is not audiable with 1ms attack time (the limiter and clipper placed after the agc, of course).
Also dealing with pre emphasis properly requires dynamic pre emp only component to be individually controlled from the rest of the audio to stop the audiable hole punching that a simple limiter seeing the whole pre emp audio causes.
Simply limiting audio at flat response, then adding pre emp is a poor way to do things.
Feedforward control does also have negative effects, proper feedback control has proven to be very sucessful.
Paul.
Less is more.
Perhaps I'm misinformed, but I believe that a compressor/expander is an EITHER/OR device; it will EITHER compress OR expand, it cannot do both at the same time.
Compressor/limiters, on the other hand, are AND devices, meaning: they will compress AND limit.
An expander is the reverse of a compressor.
A compressor forces audio energy into a smaller window of energy favoring louder average level, reducing the dynamic range.
An expander stretches the audio energy so that the low level audio is even lower and dynamic range is greater.
I don't doubt those who have said that an expander can be configured as a noise gate, but you'd need to give a detailed explanation of how this is accomplished or it is not helpful information.
Here is a link that will help: http://www.symetrixaudio.com/kb/421_ug.pdf
It's the user guide for a Symetrix 421 (which I've used in the past). The first & second chapters describe the various functions of compressor, limiter and expander (the latter for noise reduction at low signal levels), and how they work.
Thank you Artisan.
I am looking forward to learning about expanders and what they can do.
As a professional audio man in retirement it's not too late to learn about my specialty.
I have a DBX 118 Dynamic Range Enhancer. This item, circa 1970, was used to compress audio to be recorded to tape. To playback the tape, the opposite is done using the unit to expand the audio.
The idea was to effectively increase the dynamic range of audio tape (typically around 40 to 50 db) to 110 db. The end result being that the lower level passages would not be lost in the system tape noise.
I use it for its ability to compress and/or limit audio sent to the transmitter.
Sounds a little like Dolby
i run a DSP1400 ahead of a DSP9024 for FM and a DSP1400 ahead of a Inovonics 235 for AM.
as soon as a i build and load a windows pc i will be experimenting with DSP processing in windows. i have stereo tool, omnia a/xe, breakaway, and sonos 4 to choose from.
MOST (not all) of my source material is uncompressed wav for the best quality it can be.