Philip BraggI have made the PIPP limiter on a separate board and it is pleasingly symmetrical or would’ve been if I had built it more carefully
It sounds good. A lot of loud fun! Look at the spledour of spaghetti wiring. I even made a control panel.
Frans Super 🇺🇦🇵🇸🍋 FKNZS🔻@synx508 All it needs now is a seat, a steering wheel and a set of wheels. And a rear screen wiper...
(By the way, what IS a PIPP limiter?)
@apenkop It's a limiter that adjusts the gain independently for the positive and negative half cycles of the signal waveform.
@synx508 Ah! I recently saw a video about electromagnetic waves, so that rings a bell. Great work!
Andreas, DJ3EI, he/him@dj3ei @apenkop It's the final audio processing stage of Inovonics model 718 processor/stereo coder for FM broadcast, it's there to limit the amplitude to nearly the clip point. To achieve that it attempt to compensate for asymmetry without introducing too much distortion - hence this has a time constant on the gain reduction. The design includes a base-emitter shunt clipper, but there are three further clippers downstream in the full system, all are not designed to clip in all but the most extreme situations. Watching the control voltages on the oscilloscope has been interesting, I'm still digesting what I've seen.
@dj3ei @apenkop It has 4 identical time constants, one for positive and negative for each channel. The preceding stage splits the audio into three bands and does PWM controlled compression/limiting on each band, before summing them for each stereo channel. The band splitting is subtractive, so the sum always produces the same output phase response and ampllitude at any frequency, a simple approach that seems to work well enough. Preceding that is a PWM controlled AGC ±12dB of range which is also gated, to stop it gaining-up during silence. The AGC is really nice, the rest I'm not won over by but the PIPP is interesting.
PIPP = separate amplification of positive and negative half-wave in an audio system.
That was a concept new to me! Thanks, @synx508 🌹, for providing to this #hamRadio practitioner an enlightening excursion into the field of contemporary audio gain compression!
Starting from your posts 🧵, I found the publication https://www.inovonicsbroadcast.com/uploads/2017/03/31/PIPP%20White%20Paper%20(revised).pdf that describes the concept quite accessibly (assuming modest background knowledge).
(PIPP isn't meant for multi-carrier data audio signals 🙈.)