Defense Mechanism — LSDj Learning Lab: Overtones / Ghost Channel with Allpass Filter (video, 2020)

Seven minutes of a live stream by defense-mechanism, answering a viewer who asked whether LSDj can do a distorted guitar power chord. It is the 2020 answer to the 2013 hand-drawing method (s-tylerbarnes-ghost-channel-tutorial): reach the same two-note effect with the synth screen's filter instead of pixel art.

Key claims#

• The reframing, at 0:33: "this is like when people talk about — there's a video out there called the ghost channel, and it's like the idea that you can have extra notes in the wave channel. It's really talking about this overtone emphasis that sounds like almost two notes … because you've got the low note but then also that octave that's like two octaves above, or three if you use allpass with Q boosting that fifth — the power chord."
• The recipe: an allpass filter with a low CUTOFF and a high Q, "depending on where you want the signal to boost". Allpass passes every harmonic and shifts phases, so a resonant peak lifts one overtone into audibility instead of removing everything above it (the filter modes themselves are described in s-intense-tech-01-wave-synth-deep-dive-part-1).
• Why allpass rather than lowpass, at 5:10: "the nice thing about the allpass is that no matter how much you boost this Q you really never lose the root note." Lowpass is his choice when he wants the fifth to come through and the rest filtered away; allpass keeps the upper harmonics, so "it makes for a sharper sound, because you're retaining that kind of edge".
• He is candid about the limit: with Q pushed hard it is "pretty wicked", but "I don't know if I would say it sounds exactly like a guitar power chord … it doesn't not sound like a guitar chord". Around a Q of eight or nine the fifth sits right for him; below that it is "kind of subtle", above it "too much".
• Live-stream aside on his own writing habits: he keeps an allpass bass for the loud sections and a lowpass one for the rest — "another bass that's harder hitting in the chorus … where I really want more power".
• Articulation, at 3:11: with the wave set to MANUAL he drops the volume with an E01 mid-note and brings it back — "basically turn it down a little past halfway through the note and then turn it back on, to get this kind of da-da-da-da … that's almost what I would think of as a fast power chord". (E for a wave instrument is a four-step amplitude, E00–E03; see lsdj.)
• A version note in passing, at 2:10: in the version he is running "you can actually choose exactly which waveform you want in manual instead of just the synth" — the wave instrument's WAVE parameter replacing SYNTH when PLAY is MANUAL, which the 9.2.6 manual documents.

Practical takeaways#

• The cheap route to a ghost note: one synth, allpass, CUTOFF low, Q up until the wanted overtone speaks. No drawing, and the root survives any amount of resonance.
• The two filters do different jobs: lowpass for a clean, isolated fifth; allpass for a bright, aggressive one that keeps the edge.
• Gating the wave volume with E01 / E03 inside the note turns a sustained two-note wave into a chugging power chord — articulation is doing as much work as the waveform.

Notable quotes#

"It's really talking about this overtone emphasis that sounds like almost two notes."

"No matter how much you boost this Q you really never lose the root note."

Relevance to the wiki#

The second recipe on ghost-channel, and the one most people will use: a filter-built overtone instead of a hand-drawn bank. Also a rare plain statement of what allpass is for in LSDj.

To verify#

• The Q value "around eight or nine" is spoken while adjusting on screen; the CUTOFF he settles on is never said aloud (unverified).

Pages touched#

ghost-channel · filter-programming · wavetable-programming · lsdj · defense-mechanism · harmonic-series