This is my reverb in FAUST, what do you think?

Mighty23

Ideas:

Adjust gain curve to be more "exponential" for natural decay
Add smoothing to crossover frequencies to prevent zipper noise
Increase filter orders for steeper cutoffs
Use fractional delays for smoother modulation (?)

import("stdfaust.lib");

// Early Reflections
earlyReflections = par(i, 4, de.delay(ma.SR, delayTime(i)) * gain(i))
with {
    delayTime(i) = ba.take(i+1, (13, 17, 19, 23)) * 1.5;
    gain(i) = ba.take(i+1, (0.7, 0.6, 0.5, 0.4));
};

FDN = si.bus(2) : (preDelay, preDelay) <: (earlyReflections, earlyReflections, MIMO_Network ~ MATRIX) :> par(i, 2, (+:applyFilters))
with {    
    // User-controllable parameters
    decayMs = hslider("Decay[unit:ms][style:knob]", 1000, 100, 10000, 1);
    preDelayMs = hslider("Pre-Delay[unit:ms][style:knob]", 20, 0, 200, 1);
    modDepth = hslider("Modulation Depth[unit:%][style:knob]", 0.5, 0, 2, 0.01) : *(0.01);
    modRate = hslider("Modulation Rate[unit:Hz][style:knob]", 0.5, 0.1, 2, 0.1);

    // 
    // High crossover scales with decay time - longer reverbs need lower high crossover
    highCrossover = min(12000, max(2000, 8000 - (decayMs - 1000) * 0.4));
    
    // Low crossover is related to high crossover but stays within reasonable bounds
    lowCrossover = min(500, max(100, highCrossover * 0.06));
    
    // Decay ratios adapt based on decay time
    // Longer reverbs typically have more low-end build-up, so we reduce low decay ratio
    lowDecayRatio = max(0.4, min(1.2, 1.0 - (decayMs - 1000) * 0.0001));
    
    // High frequencies decay faster in longer reverbs
    highDecayRatio = max(0.3, min(1.0, 0.8 - (decayMs - 1000) * 0.0002));

    // Pre-delay
    maxPreDelay = 200;
    preDelay = de.sdelay(ma.SR * maxPreDelay / 1000, 512, preDelayMs * ma.SR / 1000);
    
    // Calculate decay factor based on milliseconds and frequency band
    calcDecayFactor(delayLengthSamples, decayMs, ratio) = pow(0.001, delayLengthSamples / (decayMs * ratio * ma.SR / 1000.0));
    
    // Matrix
    MATRIX = ro.hadamard(16) : par(i, 16, *(1/4));
    
    // Network
    MIMO_Network(fb1, fb2, fb3, fb4, fb5, fb6, fb7, fb8, fb9, fb10, fb11, fb12, fb13, fb14, fb15, fb16, in1, in2) = 
        par(i, 16, DEL(i))
    with {
        baseDelays = (3797, 3541, 3323, 3109, 2939, 2801, 2693, 2593, 2503, 2423, 2351, 2287, 2237, 2179, 2131, 2083);
        DEL(i) = de.fdelay(5000, modulatedDelay(i), fb(i) + input(i)) : multiband_decay
        with {
            delay = baseDelays : ba.selectn(16, i);
            modulatedDelay(i) = delay + os.osc(modRate + 0.01*i) * delay * modDepth;
            fb(i) = ba.selectn(16, i, fb1, fb2, fb3, fb4, fb5, fb6, fb7, fb8, fb9, fb10, fb11, fb12, fb13, fb14, fb15, fb16);
            input(i) = select2(i < 2, 0, ba.selectn(2, i, in1, in2));
            
            // Multi-band decay using automatic parameters
            multiband_decay = _ <: (
                fi.lowpass(2, lowCrossover) * calcDecayFactor(delay, decayMs, lowDecayRatio),
                fi.bandpass(2, lowCrossover, highCrossover) * calcDecayFactor(delay, decayMs, 1.0),
                fi.highpass(2, highCrossover) * calcDecayFactor(delay, decayMs, highDecayRatio)
            ) :> _;
        };
    };
    
    // Apply filters to each channel (oh! I see colours, that's so trippy :P)
    applyFilters = fi.lowpass(1, highCrossover * 1.5) : fi.highpass(1, lowCrossover * 0.5);
};    

process = FDN;

aaronventure

@Mighty23 if you use filterbank, you can be passing an argument to the function and decide on the number of bands that way.

https://faustlibraries.grame.fr/libs/filters/#fifilterbank

Also, your reverb will behave differently on different sampling rates because you're hardcoding the delay times in samples.

Modulation is also super expensive, and even if it's off, you're still running the calculations. You can bypass that using the hidden enable primitive (with ondemand coming soon)

modulatedDelay(i) = delay + enable(os.osc(modRate + 0.01*i) * delay * modDepth, modDepth>0);

Mighty23

@aaronventure Thanks for all these tips. I think I'll keep the post updated.

This is my reverb in FAUST, what do you think?

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