roboctopus — PWM, I Choose You! (2014)

Pulse-width modulation on the wave channel, where the hardware offers none: draw a square in the first wave and narrow it a little in each of the following fifteen, then let the instrument animate through them. "PWM will allow your game boy to sound a bit more like a C64, though nowhere near as smooth and classy."

Key claims#

• Start: a square pulse at VOLUME 10 (any volume works; amplitude is loudness — s-lsdj-and-you-collapse-of-the-waveform). From the SYNTH screen, SELECT+LEFT reaches the WAVE screen; the first wave of synth 8 is 80, and so on for the other synths.
• Draw: "we just need to make each frame of the pulse narrower than the one before." Sixteen waves, 0–F, moved between with B held plus LEFT/RIGHT. The labour saver: "hold SELECT and hit B twice to copy the entire wave shape … move to the next frame and hit SELECT+A to paste it so you don't have to re-draw the entire thing again." He smooths his by hand out of habit; it is not required.
• Play it: PLAY = PINGPONG, so the synth runs first wave → last → back; REPEAT F to repeat endlessly; leave LENGTH at F; a slow SPEED "will really highlight the narrowing pulse".
• The honest caveat: "You'll notice you can hear the synth stepping through each frame, unlike the smoother PWM on a C64. This is less noticeable on leads/basses in a full mix with pulse and noise instruments, and barely discernible when used in a fast arpeggio."
• Where it earns its keep: "It's great for giving a lead line a more organic feel, and it makes a pretty massive bass. It sounds great with arps, too."
• The whole thing is manual work — "it is a bit tedious, but if you want PWM in LSDJ, it's worth it".

Practical takeaways#

• Sixteen hand-narrowed waves + PINGPONG + slow SPEED is the Game Boy's answer to the SID's pulse sweep; the steps are audible, so hide them in a mix or an arp.
• Copy/paste between waves (SELECT+B B, then SELECT+A) is what makes a 16-wave bank practical at all.

Notable quotes#

"PWM will allow your game boy to sound a bit more like a C64, though nowhere near as smooth and classy."

Relevance to the wiki#

The Game Boy entry pulse-width-modulation was missing: the C64 and PC-tracker recipes were there, the wave-channel one was not.

To verify#

• The article dates from 2014, before LSDj 7's silky wave removed the click from frame changes (wavetable-programming); how much of the audible stepping survives on a current version is not tested here (unverified).

Pages touched#

pulse-width-modulation · wavetable-programming · instrument-design · lsdj · roboctopus