Amiga for Elektron Octatrack

Plays a Flex sample like an 8-bit tracker: gritty, held samples and a cyclic stretch that pulls pitch and time apart.

Module version 0.1.0-experimental. Base firmware: 1.40C.

About this module

Amiga is a track machine modelled on how a home computer's 8-bit sound chip and its tracker software played samples. It plays the track's Flex sample through the stock reader, reduces its word length and storage rate before the Octatrack repitches it, and can restart the sample every few milliseconds a little further on, so PTCH changes the pitch and SPD the length. RATE is stock's own, forwards and backwards. The track's filter, AMP, LFOs and effects follow as for any sample.

• SPD sets how fast the note moves through the sample and GRN the cycle, 96 to 4128 samples: half speed, about twice as fast or a held sound, at any pitch.
• STR can turn the stretch into a pitch shift of up to an octave either way.
• RATE is stock's own: forwards, backwards and slower, with the stretch following it both ways.
• SRR lowers the storage rate, BITS sets the word from 16 to 4 bits (8 by default), LED adds a fixed lowpass.
• RATE, SPD and GRN take parameter locks, LFOs and scenes, as SRC knobs do.

How to use it

1. Double-tap a track key (or open SRC SETUP), move to AMIGA in the machine list and press YES.
2. Double-tap the track key again and pick a sample from the Flex list, as for a Flex track.
3. Open SRC: knob D is RATE, E is SPD, F is GRN.

Controls

RATE

Stock's RATE, -64 to +63: speed and pitch together, backwards below 0. The stretch follows it both ways. SRC knob D.

SPD

How fast the note moves through the sample, whatever the pitch: 64 is its own speed, 32 half, 0 holds. SRC knob E.

GRN

The stretch's cycle, 96 to 4128 samples; 1120 by default. SRC knob F.

LED

A fixed two-pole lowpass on the stored sample. SRC SETUP knob C.

SRR

Storage rate: 16/(16+SRR) of the sample's own, each stored sample an average, then held. SRC SETUP knob D.

STR

The stretch: OFF plays as FLEX, ON stretches, PCH shifts the pitch by SPD at the note's own length. SRC SETUP knob E.

BITS

Word length from 4 to 16 bits; the saved value is bits minus 4. SRC SETUP knob F.

Compatibility notes

• USB only: it loads on the Modwerk base over USB (it needs the base's machine list and START dispatch) and has no card build.
• Experimental: played and measured on one MKII on a development base; TESTING.md lists what was not tried.
• On an MKII one Amiga track beside seven FLEX tracks added 5.5 points to the frame interrupt at the defaults and up to 13.8 with PTCH +12, SRR and LED; eight Amiga tracks reached the base's frame guard, which skipped 17 % of their renders (dropouts). Count on a few Amiga tracks, not eight.
• With a USB recording running as well, one Amiga track at PTCH +12 with SRR and LED on beside seven FLEX tracks froze the unit until a power cycle.
• No stock RTRG or RTIM on an Amiga track: SPD and GRN take their knobs.
• Stock's own time-stretch (TSTR) is off on an Amiga track, and SETUP's LEN switch is LED: the track always uses stock's default length setting.
• SRR, LED, STR and BITS are SETUP values: one for the Part, without locks or LFOs.
• A sliced track (SLIC on) is not stretched; SRR, BITS and LED still work.
• The cycle length is in samples, not tied to the tempo.
• A stretched note that is not looped ends when SPD has carried it to the end of the sample, even if LEN would stop a FLEX note sooner by time.
• A project opened without the module plays Amiga tracks as FLEX and reads SPD and GRN as stock's RTRG and RTIM, and LED, SRR, STR and BITS as SETUP's LEN, RATE, TSTR and TSNS.
• Leaving Amiga for another machine puts the track's SRC settings back to FLEX defaults.
• Before a trial of the module ends or the module is removed, put its tracks on another machine: the base refuses to take a machine away from a track that names it.

Test evidence

Host gate on the engine (verify.py, 56 checks), sample-for-sample comparison with the first build played on a unit, an emulator count of its instructions (bench.py), and RAM trials on the owner's MKII on a development base, 11 November 2026: pages, the stretch both ways, cost beside seven FLEX tracks. Worst-case cycles are not measured; no stock benchmark under a MIDI flood and no flood ran. TESTING.md lists what was not tried.