Channel interleaving (one channel, two jobs)
What it is#
When channels are scarce, interleave: bass note on every even 16th, melody notes on the odd ones. Played fast, the ear separates them into two lines — a bassline and a lead — from a single channel. The same idea works for drums + bass (kick on the beat, bass filling between) and for self-accompanying leads. Masters of 1-channel and 2-channel chip music build entire songs this way (source: s-037-lab).
How to do it#
The ghost-channel does the same accounting in the frequency domain instead of in time: two waveforms added inside one wavetable, so one Game Boy wave channel voices a bass note and a harmonic of it simultaneously, with no rows spent (source: s-chipmusic-lsdj-ghost-channel).
Alternate two instruments row by row in one channel; keep each line's notes on its own rhythmic grid so the listener's ear can stream them apart. Very short envelopes (instrument-design) help; a same-channel fake-echo is the same principle applied to one line.
Three C64 composers on it#
- jeroen-tel: "You could only use three channels, which isn't a lot. If you would compose one chord, you run out of channels. So you have to be creative. By quickly switching between three notes on one channel, you saved two channels. For example: you would have a bassline and a drum both on one channel … And so you left room for a melody. And then you also tried to put in some extra rhythm parts of fill-ins" (source: s-vgmpf-maniacs-of-noise).
- chris-huelsbeck on the per-note script of tfmx: "very short drum sounds with a fixed pitch just before a pitched bass sound … it would sound like 2 channels were used at the same time, because the human brain can't keep sounds apart that are played in very short succession" (source: s-emuwiki-huelsbeck-interview).
- matt-gray on KGB Superspy: "trying to maximise any rhythm elements without using a whole channel to do it"; on Quedex: in-game tunes "written in such a way that if a sound effect played, it didn't destroy the music too much" (source: s-c64com-matt-gray-interview).
- matt-gray on his Bangkok Knights loader, done as "my best Rob impression" of Sanxion: "I emulated that style of fast bass line with a small hat on each note. That was all one channel, but it was a good way to get some extra rhythmical or drum element in without taking a whole channel up" (source: s-vandalism63-matt-gray-interview).
Why the scene prizes it#
trixter in 1995, defending four-channel MODs: "More channels does not necessarily mean better music. Less channels, however, does mean that you need more technical skill to make something sound better" — the four-channel compos still held at Assembly and The Party, and the 20-minute-chip-compo's chip-sample time limit, were the scene's two deliberate constraints (source: s-tw033-4channel-lives-on). jeffrey-lim hoped his NNAs would not "cause the death of brilliant 4 channel music" (new-note-actions). The same value from the composers' side: quantam-porcupine (April 1996) preferred songs optimised "for as few as possible" channels — purple-motion's Minimum Velocity "because he fit it all into just 2 channels" — and tolerated 16 or 32 only when all are put to use, as in Me Tarzan, You Jane by MiG / Weird Magic (source: s-tw054-interview-quantam-porcupine); zalt (December 1995): "a good 4chn [is] much more quality than a good mchn", because "it's so much easier to make good tunes with 28 channels than 4" and spare channels invite "some 10 chnls of echo" (source: s-tw040-interview-zalt).
Multiplexing on the C64#
rob-hubbard: "Most of it was simply done by multiplexing the three channels. If the lead line has two beats rest, put a fill or some effect in there." Rather than assigning each voice a fixed role (the NES "ensemble" way: pulses for melody and harmony, triangle bass, noise drums), any sound goes on whichever channel is free. In commando the drums are spread over all three voices — noise/toms next to the lead on channel 1, ring-modulated percussion next to the arpeggio chords on channel 2, an off-beat snare alternating with the bass on channel 3 — and "there is no kick drum on the downbeat": the bassline covers it. In sanxion one channel is both the 16th-note bass and the hi-hat, because the bass instrument starts with a frame of noise (wavetable-programming). Note-stealing by sound effects (Thing on a Spring, Commando) and two-voice tunes leaving a channel for effects (The Human Race) are the same economy from the other side (source: s-newman-driving-the-sid-chip) — the effects side of the bargain is on sound-effects.
The same economy in the forum era: Jellica notes that many of the good SID hi-hats "are combined with the bass instrument or other sounds" — a noise frame inside the bass instrument rather than a channel of its own (source: s-chipmusic-sid-music-hints-n-tips; the recipe is on instrument-design).
LSDj#
The Game Boy scene's rule, from the LSDJ Advanced Tricks thread (source: s-chipmusic-lsdj-advanced-tricks): never dedicate a channel to one job. "You can have kicks, snares, toms, lead, bass and chords all in one channel and in one pattern if you mix it up and alternate" (SketchMan3); the wave channel carries kick, bass and snare (Saskrotch, Zef); arps and echoes go between pulse kicks (roboctopus); envelopes (E) let a note ring through an instrument switch (defiantsystems); "you'd be surprised at how many gaps in the music the listener's brain fills in on its own" (Victory Road); and "Dont be afraid of silence" (herr_prof). The noise-drum threads add the percussion side: one drum at a time per channel, so introduce instruments one by one and let the ear keep them (Vegasdiamond, borrowed from beatboxing), fit hi-hats on the step before with D02/D05, use the noise channel to accent a pulse bass instead of spending a channel on it (herr_prof), and layer three-channel kicks and snares (Analog) (source: s-chipmusic-noise-drum-threads).
sabrepulse's beginner tutorial teaches the trick in the very first song (source: s-sabrepulse-getting-started-with-lsdj): because the wave-channel kit kicks are "really weak and not very loud", a PULSE kick instrument (envelope F1, duty 50 %, a table with PF1 and a K00 near its end) goes on rows 0, 4, 8, C of PU1 and the bass C3 on rows 2, 6, A, E — "Kick, Bass, Kick, Bass" — leaving PU2 for the lead and NOI for snare and hats; the K00 clears the channel before each bass note (instrument-design).
In the code#
- Commando's bass patterns carry the snare themselves:
+INSTR 2,5 / A1 / 1, A2 / +INSTR 3,3 / As3 …— bass note, octave, then instrument 3 (noise, drum + octave-arpeggio flags) on the same voice — Newman's "channel 3's bassline effectively covers this function alternating with the snare" as written (source: s-realdmx-hubbard-player). - FAME's steps switch instruments per note the same way:
s3 !by $81,$a1,bd / $af,e5,d5,h4,e4,g4 / $a1,bd,$af,d5— a bass drum, an arpeggiated run, a bass drum (source: s-realdmx-audial-arts-fame-players). - Galway's Arkanoid has three voices plus a fourth track of volume-register percussion scheduled by its own pattern language — interleaving by adding a channel the SID does not have (source: s-realdmx-galway-arkanoid-player).
Heard in: a Soundmonitor tune of 1991#
- stephan-schmid on his Nicht Schlecht (1991, soundmonitor): "Here I also made my first attempt on doing a pseudo 4 channel sound, by interweaving drums and bassline" — the bass-plus-drum interleave done in a stock editor rather than a custom driver (source: s-sidin03-schmid-interview).
Related#
fake-echo · octave-bass · arrangement · chord-arpeggio
Sources#
s-037-lab · s-newman-driving-the-sid-chip · s-chipmusic-lsdj-advanced-tricks · s-chipmusic-noise-drum-threads · s-tw033-4channel-lives-on · s-sabrepulse-getting-started-with-lsdj · s-tw054-interview-quantam-porcupine · s-tw040-interview-zalt · s-vgmpf-maniacs-of-noise · s-emuwiki-huelsbeck-interview · s-c64com-matt-gray-interview · s-vandalism63-matt-gray-interview · s-realdmx-hubbard-player · s-realdmx-audial-arts-fame-players · s-realdmx-galway-arkanoid-player · s-sidin03-schmid-interview · s-chipmusic-sid-music-hints-n-tips · s-chipmusic-lsdj-ghost-channel