Envelope / Control
Delay line. The first argument is input signal, the second is delay time in samples, and the third is feedback/mix amount.
Delay time is in samples. Feedback/mix should usually stay below about 0.8 to avoid runaway feedback.
delay2(lp(pwm(0.5*X, 0.34), 0.16, 0.12), 900, 0.18)
For pitched oscillator functions, X already contains the current MIDI note pitch and transpose information. Prefer saw(X), sin(X), or pwm(X, 0.4) unless you intentionally want an octave or ratio shift such as 0.5*X or 2*X.