What it does
Live Guitar Sympathetic Strings, Octaves
Twelve sympathetic strings: the six open guitar strings, and each of them again an octave below. The guitar's own tuning across two octaves rather than a scale, so everything you play on an open string wakes both that string and its lower octave, and the bank answers with a deep bloom underneath rather than a chord beside you.
The lower strings are also the most accurately tuned in the whole family: a longer delay line gives finer pitch resolution, so E1 lands within a fifth of a cent where the top E is within six.
HOW IT IS BUILT. Twelve independent loops. Each is a summer feeding a delay line whose length sets the pitch, then a lowpass inside the loop so high harmonics decay faster than the fundamental as on a real string, then a gain just under one returning to its own summer. The twelve are added only at the output and that sum is never fed back, so the strings cannot gang up into a howl and nothing self-oscillates. Every loop gain is below unity, so the board is silent until you play.
WHAT TO REACH FOR. String coupling sets how hard your playing drives the bank. Each string's Gain sets how long that string rings; they are equal here, so the LOW strings ring longest. Raising a Gain towards 1.0 lengthens the ring steeply; at or past 1.0 the string becomes an oscillator that never stops. The Lowpass Frequency sets how bright the ring stays. Note the delay lengths compensate for that filter's own delay, so a large change to Lowpass Frequency will pull the strings slightly out of tune.
And the delay lengths are counted in SAMPLES, so the tuning above is right at 44.1 kHz and shifts with the device rate -- every string goes about +147 cents sharp at 48 kHz -- until the lengths are derived from the sample rate at load time.