core.jsfx

desc: Kai's Tone Shader (Core)

slider1:in_hp_freq=100.0<20.0, 800.0, 1.0>Input High Pass (Tightness)
slider2:in_lp_freq=12000.0<5000.0, 20000.0, 100.0>Input Low Pass (De-Noise)

slider3:drive=1.0<1.0, 50.0, 0.1>Input Drive
slider4:dynamic=0.95<0.0, 1.0, 0.01>Dynamic Sensitivity
slider5:out_gain=1.0<0.0, 2.0, 0.01>Output Gain

slider6:att_ms=100<0.1, 500, 1>Attack (ms)
slider7:rel_ms=200<0.1, 1000, 1>Release (ms)

slider10:map_mode=2<0,2,1{Hard Clip,Sigmoid (Smooth),Diode (Crunch)}>Kernel Type
slider11:diode_bias=1.0<0.1, 10.0, 0.01>Diode Bias / Asymmetry
slider12:cheby_decay=0.2<0.1, 4.0, 0.1>Harmonic Decay
slider13:odd_gain=0.8<0.0, 2.0, 0.01>Odd Harmonics (Fuzz)
slider14:even_gain=0.5<0.0, 2.0, 0.01>Even Harmonics (Tube)

slider20:oversample=1<0,1,1{Off,On (2x)}>High Quality Mode

@init
MAX_ORDER = 8;
MEM_CHEBY = 0; 

envelope = 0.0;
hp_x1 = 0.0; hp_y1 = 0.0;
lp_y1 = 0.0;

// Oversampling Filter States
os_lp_x1=0; os_lp_x2=0; os_lp_y1=0; os_lp_y2=0; // Upsample Filter
ds_lp_x1=0; ds_lp_x2=0; ds_lp_y1=0; ds_lp_y2=0; // Downsample Filter

// Core Kernel States
core_t_n1=0; core_t_n2=0;
core_dc_x1=0; core_dc_y1=0;

@slider
// 1. Envelope
att_coeff = exp(-1000.0 / (att_ms * srate));
rel_coeff = exp(-1000.0 / (rel_ms * srate));

// 2. Input Conditioners
k_hp = tan($pi * in_hp_freq / srate);
alpha_hp = 1.0 / (1.0 + k_hp);

k_lp = tan($pi * in_lp_freq / srate);
alpha_lp = k_lp / (k_lp + 1.0);

// 3. Chebyshev Weights
k_idx = 2;
dc_correction = 0; // Reset correction
loop(MAX_ORDER - 1,
    base_w = 1.0 / pow(k_idx, cheby_decay);
    is_even = (k_idx % 2 == 0);
    type_gain = is_even ? even_gain : odd_gain;
    MEM_CHEBY[k_idx] = base_w * type_gain;

    // --- CALCULATE DC OFFSET AT SILENCE ---
    // Even harmonics alternate -1, +1, -1 at silence (T2, T4, T6...)
    // Odd harmonics are always 0 at silence.
    is_even ? (
        // k_idx 2, 6, 10... are -1. k_idx 4, 8, 12... are +1
        sign = ((k_idx / 2) % 2 == 1) ? -1 : 1;
        dc_correction += sign * MEM_CHEBY[k_idx];
    );

    k_idx += 1;
);
rest_scaler = 1.0 - dynamic;
dc_correction *= rest_scaler;

// 4. Anti-Aliasing Filter (2x Rate Biquad Butterworth)
// Cutoff @ 20kHz to protect audio band
os_cut = 20000;
os_w0 = 2 * $pi * os_cut / (srate * 2); 
os_cos = cos(os_w0);
os_alpha = sin(os_w0) * 0.70710678;

lp_b0 = (1 - os_cos) / 2;
lp_b1 = 1 - os_cos;
lp_b2 = (1 - os_cos) / 2;
lp_a0 = 1 + os_alpha;
lp_a1 = -2 * os_cos;
lp_a2 = 1 - os_alpha;

lp_b0 /= lp_a0; lp_b1 /= lp_a0; lp_b2 /= lp_a0;
lp_a1 /= lp_a0; lp_a2 /= lp_a0;

@sample
input = spl0;

// A. Input Conditioning (Band Limit)
hp_out = alpha_hp * (hp_y1 + input - hp_x1);
hp_x1 = input;
hp_y1 = hp_out;

conditioned_sig = hp_out * alpha_lp + lp_y1 * (1.0 - alpha_lp);
lp_y1 = conditioned_sig;

// B. Dynamics Detection
target = abs(conditioned_sig);
target > envelope ? (
    envelope = envelope * att_coeff + target * (1.0 - att_coeff);
) : (
    envelope = envelope * rel_coeff + target * (1.0 - rel_coeff);
);
env_scaler = (dynamic * min(1.0, envelope * 10.0) + 1.0 - dynamic);

base_sig = conditioned_sig * drive * env_scaler;


iter_count = oversample ? 2 : 1;
final_out = 0;
loop_idx = 0;

loop(iter_count,
    
    // --- A. Upsample (Interpolation) ---
    curr_in = 0;
    oversample ? (
        // Zero Stuffing: Frame 0 = Signal*2, Frame 1 = 0
        loop_idx == 0 ? raw_in = base_sig * 2.0 : raw_in = 0.0;
        
        // Apply AA Filter
        curr_in = lp_b0*raw_in + lp_b1*os_lp_x1 + lp_b2*os_lp_x2 - lp_a1*os_lp_y1 - lp_a2*os_lp_y2;
        os_lp_x2 = os_lp_x1; os_lp_x1 = raw_in; os_lp_y2 = os_lp_y1; os_lp_y1 = curr_in;
    ) : (
        // No Oversample: Pass through
        curr_in = base_sig;
    );

    // --- B. The Kernel (Non-Linear Math) ---
    
    // 1. Mapper
    cheby_in = 0;
    map_mode == 0 ? (
        cheby_in = max(-1.0, min(1.0, curr_in)); // Hard Clip
    ) : map_mode == 1 ? (
        cheby_in = 2.0 / (1.0 + exp(-curr_in * 2.0)) - 1.0; // Sigmoid
    ) : (
        curr_in >= 0 ? (
            cheby_in = 1.0 - exp(-curr_in);
        ) : (
            cheby_in = -1.0 + exp(curr_in * diode_bias);
        ); // Diode
    );
    cheby_in = max(-1.0, min(1.0, cheby_in));

    // 2. Chebyshev Synthesis
    core_t_n1 = cheby_in; 
    core_t_n2 = 1.0;
    cheby_sum = core_t_n1; 

    c_k = 2;
    loop(MAX_ORDER - 1,
        t_n = 2.0 * cheby_in * core_t_n1 - core_t_n2;
        w = MEM_CHEBY[c_k] * env_scaler; 
        cheby_sum += t_n * w;
        core_t_n2 = core_t_n1;
        core_t_n1 = t_n;
        c_k += 1;
    );
    cheby_sum -= dc_correction * (env_scaler / rest_scaler);

    // 3. DC Blocker (High Rate)
    curr_sat_out = cheby_sum - core_dc_x1 + 0.999 * core_dc_y1;
    core_dc_x1 = cheby_sum;
    core_dc_y1 = curr_sat_out;
    

    // --- C. Downsample (Decimation) ---
    oversample ? (
        // Apply AA Filter again to cut ultrasonic harmonics
        ds_out = lp_b0*curr_sat_out + lp_b1*ds_lp_x1 + lp_b2*ds_lp_x2 - lp_a1*ds_lp_y1 - lp_a2*ds_lp_y2;
        ds_lp_x2 = ds_lp_x1; ds_lp_x1 = curr_sat_out; ds_lp_y2 = ds_lp_y1; ds_lp_y1 = ds_out;
        
        // Keep Frame 0, Drop Frame 1
        loop_idx == 0 ? final_out = ds_out;
    ) : (
        final_out = curr_sat_out;
    );

    loop_idx += 1;
);

// --- Stage 3: Output ---
spl0 = final_out * out_gain;
spl1 = spl0;