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Limiter DSP for LFE channel
Matt:
I don't think the sliding cross-over frequency idea is a keeper. When you change a parameter of an IIR filter, you need to reset it which causes it to change behavior for a little bit. That means it's not a good candidate for being continually adjusted.
Instead, I think a series of a few cross-over filters would be better. I think you could break the signal into a two or three buckets, then limit each bucket separately. The limiter would only engage when the sum of all the buckets exceeds the set limit, meaning it would work better than the approach you mentioned using in Parametric Equalizer. As long as it's designed properly, the sum of all the buckets should make no changes when the limiter is not engaged.
But I need to figure out conceptually the right way to engage the limit. Should it be willing to bring 20Hz down to zero to preserve 80Hz? Or is there some relationship, where it's willing to bring 20Hz down 4x as much as 80Hz or similar?
In other words, what should limiting do with the following scenarios to get the total to 100% or less:
20Hz: 200%; 80Hz: 0%
20Hz: 0%; 80Hz: 200%
20Hz: 200%; 80Hz: 100%
20Hz: 100%; 80Hz: 200%
Matt:
I'm sort of talking to myself here, but I think I've figured out something that would work well.
You take the incoming signal and split it with a low-pass / high-pass combination at like 50 Hz with 12dB/octave filters. This gives you the low and high components.
Then, when the signal crosses the limiting threshold, you run the limiter in two stages.
First, you bring the low all the way down to zero.
If it still needs limiting, you bring the highs down.
Since you have a 12dB/octave slope on the highs, even when you bring the lows all the way to zero you still have a nice smooth frequency response slope.
I think this whole thing results in a reasonably simple design that would nicely accomplish the goal of limiting the lowest frequencies more than higher frequencies.
JustinChase:
--- Quote from: Matt on September 13, 2012, 11:10:26 am ---I'm sort of talking to myself here
--- End quote ---
sort of?? ;D
Matt:
An improved subwoofer limiter is in tonight's build.
Thanks to mojave for the idea (almost two years ago).
The actual implementation tuned some of the parameters I listed above, but the general idea is the same.
(p.s. if you had tried the subwoofer limiter in past builds, please remove it and add one of the new style; the old style was removed)
mojave:
I just tried this out and can't notice any difference whether it is on/off or varying dB level settings. I downloaded and played Jurassic Lunch which has content down to 10 Hz. I played back multiple times and watched it in GlissEQ. I had all my amps off and the volume set to 100%
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