Lightweight but decent limiter algo

[bootsy]

Hiho,

thanks to kirkagur who posted sometimes ago somewhere a simple but really decent limiter algorithm I've stripped it down to avoid the cpu expensive log encoding of the entire stream data. Saves tons of cpu without sounding worse.

I've attached both versions.

peace,
bootsy

[infuzion]

Thanks for sharing!
For an even more light weight limiter:

Code: Select all

streamin i;streamout o;
float Fmin=0.999;
float Fmax=-0.999;
movaps xmm0,i;
minps xmm0,Fmin;
maxps xmm0,Fmax;
movaps o,xmm0;

But won't sound as sexy as the ones above, since this is more of a clipper-limiter, where that is more like a static-compressor-limiter

[aliasant]

Hey. What is the difference between this static limiter and any clipper?

[infuzion]

Hey. What is the difference between this static limiter and any clipper?

My ASM code is indeed a "clipper" which is a subset of limiters:
http://en.wikipedia.org/wiki/Limiting
I believe the above OSM has "soft limiting", due to a sort of compression to it.

Each have their uses; mine is better if an OSC or a ENV on rare occation touches outside of the +/-1.0 boundaries of a signal, as a final peak tamer when 99.99% of the signal is under max but you are pressing to CD, or if you crank up the volume & want that icky digital sound that dance tracks have now. Soft limiting is better for a more musical taming of peaks, like to hone in the occasional peaks of a vocal track after you compressed it, or part of the mastering process.

[aliasant]

OK.
Well.
As I see it a limiter is a compressor with a high Ratio and high threshold.
Often the ratio is at or above 10:1 and the threshold might be -6 dB or so. There should be no attack but a variable release time. Thats why you had me a bit confused

[bootsy]

Be aware that soft-limiting introduces aliasing if not oversampled to the right amount and hard-clipping introduces heavy aliasing in any case (can't be compensated).
So an envelope driven approach (which features less distortion) might be more suitable in most cases.

[exonerate]

I believe the above OSM has "soft limiting", due to a sort of compression to it.

It's not correct to call it soft limiting, soft limiting/clipping doesn't actually clip it just distorts the waveshape so that it doesn't go above one. The higher the amplitude is above one the greater the distortion, which can be good sometimes for the 'analog' sound, basically a saturation algo on your output is soft limiting.

Hard limiting is actually clipping in that it clips the top of the waveform off, also affecting the sound.

Neither hard or soft limiting take into account the current amplitude.

kirkagurs/bootsys example would be a brickwall limiter, which justs adjusts the amplitude when it goes above one and doesn't distort the waveform like the other methods.

Thanks for this bootsy I think I'm going to use this on my synth, I've been playing around with limiting methods, I wanted to use a brickwall limiter but I couldn't make one efficent enough, but this one is thanks

Cheers

Exo

[exonerate]

Ok I saw some glaring obvious optimizations so I just couldn't help my self .......

limiter ASM.osm

(1.98 KiB) Downloaded 370 times

Now the limiter is inside one ASM block, I've not checked the CPU usage but It will be considerabily less.

Cheers

Exo

[bootsy]

Awesome, Exo!

I'm now setting up a basic compressor without logencoding just to see how far we can go avoiding expensive log or exp operations. It already features attack and release control, simple ratio control and even soft knee.
The only drawback I can see at the moment is that the attack and release curve shape is different than on a logencoded stream but I maybe err on that.

[infuzion]

...hard-clipping introduces heavy aliasing in any case (can't be compensated).

Very true! That's why most of the scenarios I listed I was expecting the signal to be over only 0.0001 or so.

[aliasant]

OK. Here is my latest small limiter code as asm. It is not optimized. I just turned it into asm to keep my secrets.
We really do need lockable modules!

There is a variable release ( same as the envelope follower we already have)
You can push it to about -60 dB reduction before it squeels. The louder the input the longer the release time needs to be.
At least if you dont want to much aliasing.

Oh. If you want to see how much it is compressing the signal use the red output. Hook it into a linear to dB converter.
You could do that in green.
Maybe someone can optimize this?

Code: Select all

//Limiter Code by Martin Rodensjo / aliasant
streamin in;
streamin release;
streamout out;
streamout red;
float rectified=0;
float c=0;
float thres=0;
float x=0;
float x1=0;
float env=0;
float F1=1;
float F0=0;
float F2=2;
float F1eM008=1e-008;
float F0P001=0.001;
float F1000=1000;
movaps xmm0,in;
cmpps xmm0,F0,1;
movaps xmm1,xmm0;
andps xmm1,F2;
movaps xmm2,F1;
subps xmm2,xmm1;
movaps xmm3,in;
mulps xmm3,xmm2;
movaps xmm4,xmm3;
addps xmm4,F1eM008;
//Assignment> sLeft=xmm4
movaps rectified,xmm4;
movaps xmm0,rectified;
subps xmm0,F0P001;
//Assignment> sLeft=xmm0
movaps x,xmm0;
movaps xmm0,F1000;
minps xmm0,x;
//Assignment> sLeft=xmm0
movaps x,xmm0;
movaps xmm0,F0;
maxps xmm0,x;
//Assignment> sLeft=xmm0
movaps x1,xmm0;
movaps xmm0,x1;
cmpps xmm0,env,5;
movaps xmm1,F0;
subps xmm1,release;
andps xmm0,xmm1;
movaps xmm1,release;
addps xmm1,xmm0;
//Assignment> sLeft=xmm1
movaps c,xmm1;
movaps xmm0,env;
subps xmm0,x1;
movaps xmm1,c;
mulps xmm1,xmm0;
movaps xmm2,xmm1;
addps xmm2,x1;
movaps xmm3,xmm2;
subps xmm3,F1eM008;
//Assignment> sLeft=xmm3
movaps env,xmm3;
movaps xmm0,env;
addps xmm0,F1;
movaps xmm1,F1;
divps xmm1,xmm0;
//Assignment> sLeft=xmm1
movaps red,xmm1;
movaps xmm0,red;
mulps xmm0,in;
//Assignment> sLeft=xmm0
movaps out,xmm0;


[aliasant]

Wow. I just compared the Kirkagur Limiter (optimised by you guys) and my own and they sound and act very very similar.
But the code is not that similar.
I made it in a different way and I think my limiter might sound better with shorter release times.
Probably because of the way I did the threshold but Im not sure.
They do sound alike with higher release times though. Very much alike.

[exonerate]

Bootsy do you mind me adding this limiter to the Developer toolkit ?

Cheers

Exo

[infuzion]

Ok I saw some glaring obvious optimizations so I just couldn't help my self.. Now the limiter is inside one ASM block, I've not checked the CPU usage but It will be considerably less.

That's some tight ASM! I can't do better
/bow

[bootsy]

Bootsy do you mind me adding this limiter to the Developer toolkit ?

Cheers

Exo

If it's ok to kirkagur its fine to me