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e3c8830b45
- Update the comments to correctly describe the Klon as a hard-clipping circuit (diodes to ground) rather than a soft-clipping one (diodes in feedback). - Update the clean/dirty blend calculation so that clean_amt reaches 0.0 at maximum drive, matching the dual-gang mix pot on the real Klon. - Convert the input coupling High-Pass (in_hp) and input bandwidth Low-Pass (pre_lp) from 2-pole Biquads (12dB/octave) to 1-pole RC filters (6dB/octave) using the existing single_pole_hpf and single_pole_lpf functions. Using single-pole functions instead of biquads should make the effect cheaper to run too - not that the Klon was expensive before either. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
106 lines
3.9 KiB
C
106 lines
3.9 KiB
C
// NAME: Klonlike [KLON]
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// PRIORITY: 50
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// POT: "Gain" LINEAR(0 1) = 0.20
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// POT: "Treble" LINEAR(0 1) = 0.50
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// POT: "Output" LINEAR(0 1) = 0.40
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// Klon pedal originally by Bryan Leavelle <bryanleavelle@gmail.com>
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//
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// Circuit modeled:
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// Charge pump (18V headroom) -> input buffer -> op-amp driving germanium
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// diodes (1N34A) to ground for hard clipping -> clean/dirty blend that tracks
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// gain knob -> treble control with 1.7kHz presence peak.
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//
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// The Klon's signature: the clean/dirty blend is NOT a mix knob -- it's
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// wired to a dual-gang gain pot. Low gain = mostly clean with a touch of edge.
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// High gain = 100% clipped. The clean signal grounds out as gain increases.
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/* ------------------------------------------------------------------ */
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/* DC blocker — 1-pole HP at ~20Hz */
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/* ------------------------------------------------------------------ */
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// NOTE! Bryan's original code didn't have the 2*pi correction, and so
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// the alleged 20Hz filtering was actually a high-pass filter at around
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// 3.2Hz.
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//
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// The real Klon Centaur has a 100nF input blocking capacitor with a
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// 1M resistor to ground, so the DC blocking is actually more like a
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// 1.5Hz high-pass filter.
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//
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// The output DC blocking is a 4.7uF cap with a 100k pulldown, which
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// is even lower, but at that point we're so far away from any audio
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// frequencies that it doesn't matter at all and we'll just use this
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// for both cases
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static inline float klon_dc_step(struct single_pole_state *state, float x)
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{
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return single_pole_hpf(x, state, single_pole_rc(1e6, 100e-9));
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}
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struct {
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float drive, treble, level;
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struct single_pole_state dc_in; /* DC blocking at input */
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struct single_pole_state dc_out; /* DC blocking at output */
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struct single_pole_state in_hp; /* 30Hz coupling cap */
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struct single_pole_state pre_lp; /* 15kHz input bandwidth */
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struct biquad tone_hs; /* treble control — hi shelf @ 2kHz */
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struct biquad pres_pk; /* presence peak @ 1.7kHz */
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} klon;
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void klon_init(unsigned char pot[10])
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{
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klon.drive = klon_pot0(pot[0]);
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klon.treble = klon_pot1(pot[1]); // 0 = dark, 1 = bright
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klon.level = klon_pot2(pot[2]);
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float hs_db = (klon.treble - 0.5f) * 12.0f; // -6 to +6 dB
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float peaking_db = klon.treble * 6.0; // 0 to +6 dB (original effectively doubled the boost)
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// Single-pole RC filters for coupling and bandwidth
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// initialized implicitly to 0 by static allocation, no init needed here
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biquad_highshelf(&klon.tone_hs, 2000.0, 0.7, db_to_level(hs_db));
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biquad_peaking(&klon.pres_pk, 1700.0, 1.5, db_to_level(peaking_db));
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}
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float klon_step(float in)
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{
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float drive = klon.drive;
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float level = klon.level;
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float pre, boost, ge_clip, clean_amt, dirty_amt, mixed, y;
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/* Input conditioning */
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pre = klon_dc_step(&klon.dc_in, in);
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pre = single_pole_hpf(pre, &klon.in_hp, single_pole_freq(30.0)); /* coupling cap */
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pre = single_pole_lpf(pre, &klon.pre_lp, single_pole_freq(15000.0)); /* input bandwidth */
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/* Op-amp gain — 18V charge pump gives ~2x headroom vs 9V pedals */
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boost = 1.0f + drive * drive * 55.0f;
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pre = pre * boost;
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/*
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* Germanium diode pair (1N34A) to ground — 0.3V forward voltage
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* (silicon is 0.7V — germanium clips softer, rounder, more compressed).
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* Hard clipping to ground gives even harmonic content from the soft knee.
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*/
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ge_clip = tanhf(pre * 0.45f) * 1.8f;
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/*
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* THE KLON'S SIGNATURE: clean/dirty blend tracks the gain knob via a
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* dual-gang pot.
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* Low drive = mostly clean with a whisper of edge.
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* High drive = 100% clipped, clean signal is fully grounded out.
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*/
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clean_amt = 1.0f - drive;
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dirty_amt = drive;
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mixed = in * clean_amt + ge_clip * dirty_amt;
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/* Post-clip tone shaping */
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y = biquad_step(&klon.tone_hs, mixed); /* treble shelf */
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y = biquad_step(&klon.pres_pk, y); /* 1.7kHz presence peak */
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y = klon_dc_step(&klon.dc_out, y); /* remove clipping DC offset */
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return y * (0.3f + level * 1.5f);
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}
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