Gain Reduction Meter on a Faust compressor

[Christoph Hart]

@aaronventure the vbargraph UI element in Faust translates to a mod output.

[Mighty23]

@udalilprofile @aaronventure

import("stdfaust.lib");

/* Controls */
comp_group(x) = hgroup("1-compression", x);
env_group(x)  = vgroup("2-envelop", x);
gain_group(x) = vgroup("3-gain", x);
link_group(x) = vgroup("4-channel linking", x);

// Controls
ratio     = comp_group(nentry("ratio", 2, 1, 20, 0.1));
threshold = comp_group(nentry("threshold", -20, -96, 10, 0.1));
knee      = comp_group(nentry("knee", 3, 0, 20, 0.1));
attack    = env_group(hslider("attack [unit:ms]", 2, 0, 1000, 0.1) : /(1000)) : max(1/ma.SR);
release   = env_group(hslider("release [unit:ms]", 500, 0, 10000, 1) : /(1000)) : max(1/ma.SR);
makeup_gain = gain_group(hslider("makeup gain", 0, -96, 96, 0.1));

// Control for channel linking  - stereo vs dual mono.
channel_link = link_group(hslider("channel link", 100, 0, 100, 1) : /(100));

// Envelope detector
t = 0.1;
g = exp(-1/(ma.SR*t));
env = abs : *(1-g) : + ~ *(g);

// Compression function 
compress(env) = level*(1-r)/r
with {
    level = env : h ~ _ : ba.linear2db : (_-threshold+knee) : max(0)
    with {
        h(x,y) = f*x+(1-f)*y with { f = (x<y)*ga+(x>=y)*gr; };
        ga = exp(-1/(ma.SR*attack));
        gr = exp(-1/(ma.SR*release));
    };
    p = level/(knee+0.001) : max(0) : min(1);
    r = 1-p+p*ratio;
};

// Gain computer for a single channel
gain_computer(x) = env(x) : compress : gain : +(makeup_gain) : ba.db2linear
with {
    gain(x) = attach(x, x : gain_group(hbargraph("gain", -96, 0)));
};

// Gain reduction calculation (in dB)
gain_reduction(env) = env : ba.linear2db : (_ - compress(env)) : min(0);

// Main process
process(l,r) = (gl*l, gr*r)
with {
    g_left = gain_computer(l);
    g_right = gain_computer(r);
    g_linked = max(g_left, g_right);
    
    gl = g_left*(1-channel_link) + g_linked*channel_link;
    gr = g_right*(1-channel_link) + g_linked*channel_link;
    
    
    gainReductionLeft = gain_reduction(l) : hbargraph("[5]Gain Reduction Left[style:numerical]", -60, 0);
    gainReductionRight = gain_reduction(r) : hbargraph("[6]Gain Reduction Right[style:numerical]", -60, 0);
};

@udalilprofile said in Gain Reduction Meter on a Faust compressor:

Hello. Were you able to solve the problem? What compressor are you using?

I'm still trying, as soon as I can get a decent version I'll post a snippet.

[udalilprofile]

@Mighty23 thnx)

[trummerschlunk]

@Christoph-Hart How exactly would I access the 'mod output' of a vbargraph UI element?
My goal is to simply put a meter from my faust code on the interface.

[aaronventure]

@trummerschlunk Right now you can't because the mod output goes away once you compile the node and you can only use a compiled Faust node within ScriptNode.

[Engine/ScriptNode/Faust] Compiling a Faust node with vbargraph outputs doesn't preserve them in the compiled node · Issue #619 · christophhart/HISE

If you use vbargraph in Faust, it will create a cable output in the node, but the cable outputs will not be present on the compiled node. something = 0.3; somethingElse = 0.5; intermediary = something * somethingElse : vbargraph("[0]Cabl...

GitHub (github.com)

But to answer your question, you would just pass your GR through vbargraph.

Let's say you're calculating it separately so

gainReduction = gain reduction math here : vbargraph("GainReduction",0,1);

Faust Syntax - Faust Documentation

(faustdoc.grame.fr)

[trummerschlunk]

@aaronventure so I understand correctly: no workaround?

[aaronventure]

@trummerschlunk depends on what you're metering. If it's just the gain reduction, you can have a peak node before the faust node and another right after, subtract these to get the difference (do it in the modchain so that it doesn't affect your audio signal) and there's your gain reduction.

If you're metering something else, you can do one of two things:

• run a multichannel scriptnode (4 channels for example) with a 4 channel faust effect and simply output whatever you're metering to the other two channels, get them specifically with a multi node (to separate the channels) and use that in your interface
• create another version of your faust effect where you're outputting whatever your metering and just connect it to the same parameters as your main faust effect (keep in mind that, since you're gonna be doing this in modchain, you only need one channel out of faust as modchain is a single channel node

[trummerschlunk]

@aaronventure ok, thanks...
For me it's not about gain reduction, so I hope the first option for 'metering something else' will work. I have a lot of meters though... 20 to be precise...

[sletz]

@trummerschlunk see my answer here: https://faustdoc.grame.fr/manual/syntax/#attach-primitive

[trummerschlunk]

Thanks, @sletz, I am aware of the attach primitive. The problem is that no metering signals are available in HISE when the dsp network is compiled.