Defense Mechanism — LSDJ Wave Channel Tutorial..? (More of a ramble) (video, 2020)

The video companion to the Wave Synth Deep Dive articles (s-intense-tech-01-wave-synth-deep-dive-part-1, s-intense-tech-02-wave-synth-deep-dive-part-2), demonstrated with an oscilloscope on screen. Two things make it worth its own summary: the synth frame chart, written out in the description and therefore not subject to transcription error, and a live walk up the harmonic series that reaches partials the articles stop short of.

Key claims#

• The synth frame chart (author-written, from the description). LENGTH does not shorten the run from wave 0 to wave F; it decides how many of the 16 waves are generated and spreads them evenly, so the synth always travels 0 → F, just in fewer steps:

In his words at 30:16: "if we shorten LENGTH it doesn't just play from zero to E … it actually always plays from zero to F, but it will only play as many frames and it will interpolate those … it kind of skips frames in the middle to equalize them." He wrote the chart hoping it would reach the manual.

• The filters are not filters. At 6:49: "the fun thing about LSDj is it kind of emulates different filter types, and this is a wavetable synthesizer, it's not a subtractive synthesizer — so the filters that you see here are actually just kind of emulated, they're not real filters. It will just generate what you might expect to see from these kinds of filters." The filtering happens when the 16 waves are generated, not on the output.
• CUTOFF's first digit is the harmonic number, demonstrated by ear with bandpass and a high Q from 10 upwards: 10 the fundamental ("close to a sine wave"), 20 an octave, 30 a fifth above that, 40 another octave, 50 a major third, 60 another fifth, 70 "an out-of-tune kind of seventh", 80 another octave, 90 "like a major second", A0 "another major third", B0 "a sharp fourth", C0 a fifth, D0 "almost like a sixth … kind of a flat seventh"; above that "it probably only generates up to here really". This extends the wiki's 20/30/40 rule up the whole series.
• Signals as harmonic content: saw = every harmonic ("in the case of LSDj I think it's up to 15"); square = the odd harmonics, and he verifies it live — on a square, CUTOFF 20 changes nothing but the volume ("we don't get that second octave … we have to go up to 30, and we don't get the octave, we get a fifth"); the triangle/sine option has the odd harmonics falling off "twice as quickly", and is not a true sine because "doing pure sine-wave math on the Game Boy isn't an exact science".
• Adding an overtone is multiplying the wave. At 23:07–24:24, with the oscilloscope: raising CUTOFF from 10 to 20 "kind of replicate[s] your waveform … every time you add an extra overtone you multiply the waveform", and PHASE RESYNC does the same thing by another route — "when we add more phases we're actually just kind of adding more copies of the waveform … so this is basically the same as what we just had". A third-party statement of the mechanism the ghost-channel exploits.
• DIST and PHASE, plainly: CLIP rounds anything past 0 or F off to 0 or F; FOLD mirrors it back; WRAP sends it out the other side ("if it goes past F then the next value will come up from 0") and gives "all kinds of extra harmonics … and a wider dynamic range … so it's gonna be louder and just more intense", ending in noise if pushed. RESYNC duplicates the wave in full — "a good way to really get high harmonics quickly"; RESYNC2 "will kind of cut off this waveform with another copy … usually has the effect of being like the regular resync but just quieter". A version note at 33:49: PHASE 1F "is not total silence as it used to be, it's actually just this waveform".
• LIMIT as the wave channel's real volume control (34:59–39:00). The E steps are "25 %, 50 % and a hundred percent, and there's nothing between fifty and a hundred … sometimes 2 is too soft for an instrument and 3 is too loud in the context of your mix". Instead: set LIMIT 0 on the first wave and F on the last, PLAY LOOP with the loop point at the end so it sustains, and the instrument performs its own sidechain pump — "now we can have this going from zero to F and have this kind of naturally do its own sidechaining", with SPEED and LENGTH setting how fast the duck recovers, and a start value above 0 if the duck should not go silent. "You could do more than LIMIT too — you could do VOLUME here, you could do Q." He notes this was impractical before the wave channel stopped clicking: "it's something that I wasn't really exploring, because the wave channel was just so clicky, whereas now it's really possible to do this."
• Instrument playback settings: SPEED is in ticks per wave frame; ONCE plays through and stops; LOOP returns to the LOOP POS (at the end = sustain on the last wave); PINGPONG runs to the end and back. VSHIFT he leaves alone — "I haven't really found a really super effective way to use VSHIFT".
• Historical framing (1:43–2:49): original Game Boy games loaded a waveform for a level or a section, "chosen somewhat carefully by the programmers or the composer to kind of make it sound like a trumpet or a flute"; LSDj gives "way more control over the waveform than any programmer ever had", with Game Boy Color titles doing more "wave channel shenanigans" thanks to the faster CPU and extra memory.

Practical takeaways#

• Read CUTOFF as a harmonic number and Q as how much of that harmonic you want; the filter is a harmonic selector, not a tone control.
• Use LENGTH to change resolution, not endpoint: the synth always ends on wave F.
• For wave-channel dynamics finer than E01/E02/E03, ramp LIMIT across the synth and let the instrument duck itself.

Notable quotes#

"This is a wavetable synthesizer, it's not a subtractive synthesizer — so the filters that you see here are actually just kind of emulated."

"Every time you add an extra overtone you multiply the waveform."

Relevance to the wiki#

The frame chart is a fact the manual does not state; the "filters are emulated" line corrects a natural misreading of the synth screen; and the LIMIT-ramp gives sidechain-pump a real LSDj wave-channel recipe.

To verify#

• The upper partials (90 and above) are named by ear on a stream, and he corrects himself twice while doing it; the intervals match the harmonic series but the exact naming above 80 is unverified.
• "Up to 15" harmonics in the LSDj saw is said with hesitation ("I think"); the deep-dive article says the same in the same hedged way (unverified).

Pages touched#

lsdj · wavetable-programming · filter-programming · harmonic-series · sidechain-pump · volume-slides · ghost-channel · defense-mechanism · levels-and-headroom