Stereo Tool

Hello to everyone,

I recently noticed at the largest private radio station in Germany that during processing, not on the Internet but on DAB+ or FM, they use a post AGC at the end of the process chain to straighten the signal even further after the clippers. This can look quite bizarre in recordings because the AGC can be seen very clearly. But what I noticed is that the sound becomes more comfortable. It is still a good compression, but very loud parts are reduced more easily.
I tried to adjust the whole thing with two StereoTools one after the other and the result amazed me. You only notice the volume changes subconsciously. But it all does not seem so crushed.
So my question would be, how complex would it be to provide an AGC after the clipper, which makes the signal more even and thus gives the signal a certain softness.
Or maybe I am completely wrong here and this has something to do with BS412 and that's where it comes from. In StereoTool I can't reproduce this without an additional AGC to have such a wave pattern in the final result. Maybe there are experts among us who can describe this in more detail. Maybe there is a deeper meaning behind it. In any case the final result is very relaxing and much more even than without AGC at the end.

Are you 100% sure that they use AGC after limiter/clipper? Since proper HD preset can 'look' like it uses AGC after final limiter/clipper. Simply more dynamic track will go more into limiter/clipper more, and less or no dynamic tracks can go under limitter/clipper treshold. Usually my HD presets are like that. It's even more noticable when you don't use DeClipper, Natural Dynamics and PhaseRotator, and input is ofcourse perfect.

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control point
control point2

Interesting. Thanks for the possible explanation. Unfortunately I do not know exactly. It was only a guess and I came to this result with an additional AGC. I will try the one you suggested. But maybe you can explain to me, if you have created similar results in your presets, the results somehow sound better than if you used a hard clipper at the end? It all sounds much smoother and somehow rounder in itself.

It always depends what you want form sound. We all know that limiter or clipper is better to use as little as possible. If you are on that way, and certainly you want to maintain same loudness/rms with your AGC and MB on every input.. then it will happen. Nice and dynamic track will hit your limiter with 1 or 2dB, however loud and clipped/compressed tracks will go under that limiter/clipper threshold because it will be pushed down by AGC and MB.
Try only that. Use only AGC, MB and Limiter/Clipper. It's anyway always good to start from there and make it perfect when you make preset. Everything else is just make-up.

Here is switch from one to another track..

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control point
control point2

So I tested it. Yes the result is indeed very close to the result shown above. Thanks for the info, I learned a lot. So far I have put a lot of emphasis on the integrated clipper, but I find your approach to this very exciting. What I also found exciting is your recommendation to do without the Declipper or Natural Dynamics. I felt the biggest difference when I switched off Natural Dynamics. I didn't realize that Natural Dynamics changes the signal so much when using the clipper extensively, but unfortunately not necessarily for the better, but rather for the worse.

Now I'm going to experiment with it a bit more over the days. You have given me some very good food for thought! Many thanks for that.

Of course this effect is seen more often on BS412-restricted broadcasts because there is no loudness advantage of clipping everything to hell. You would not see an effect like this on a dutch radio station, for example (unfortunately). Part of the effect can also be a BS412-leveler which could in theory have been implemented after the clipper...

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Imaging producer & Stereo Tool audio processing consultant