The limiter on the ESP page is pretty good - fast attack, reasonably low distortion, and an adaptable decay (recovery) time. I've used versions of this type of circuit for years. The only real problem you're likely to encounter is matching FETs for a stereo pair, and commoning the sidechains so that the stereo image remains consistent when the gain reduction kicks in.
The other issue with a simple limiter like this is that a big bass thump will dip out the midrange and treble. This will make that audio "pump" - really not too good with most modern forms of music!
The "pumping" can be mitigated by splitting the audio into bass and the rest, and separately processing them - you're going to need four matched FETs! The outputs of the bass and mid / top limiters (for each channel) can be combined after processing, and the pumping problems will be largely eliminated.
Here's one way of doing it.....
Split-Band Limiter.png
I'm thinking a doing a PCB for this circuit, with a few additional options provided on the board: -
- Pre-emphasis at 50µs or 75µs on the way in,
- An option to introduce delay lines to the audio paths to allow "zero attack time" processing,
- Audio filtering to get rid of content above 15 kHz,
- A post-process clipping option.
The 15 kHz filters and the delay lines would be on additional plug-in boards, and I've designed a very high quality stereo coder and an optional RDS board to work nicely with this unit. I also planned to add LED bargraphs to show "gain reduction" (the uninitiated love blinking lights), using more LM339s, and even a silence alarm.....
The whole package would be functionally equivalent to something like the Inovonics "David" processor / coders, and would sound a whole lot better than most UK commercial radio ststions!
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