Torso T-1 backup format (.t1) ⇄ MIDI

Reverse-engineering the Torso Electronics T-1 sequencer's backup format so patterns can be exported to and imported from standard MIDI files — and so a bank can be rebuilt from scratch and loaded back onto the hardware.

The format is fully worked out for the musically meaningful fields: every archived device backup in this repo rebuilds byte-for-byte, and synthesized banks (chords, cycles, split drum kits) have been loaded and verified on real T-1 hardware.

Built with Claude Code

This project — the reverse engineering, the byte-map, the tooling, and this documentation — was produced through heavy use of Claude Code (Anthropic). The workflow was collaborative: the hardware owner captured device backups on request (targeted parameter sweeps), and Claude Code diffed them, located the fields, wrote the codecs, and drove the round-trip and on-device verification. It is genuinely an AI-assisted RE effort, not a hand-written library, and the commit history reflects that.

What this is

The T-1 has no documented save format. Its backup is a ZIP whose banks are opaque binary blobs. This repo decodes that blob into a clean data model and back again:

 .t1 bank  ──▶  t1_format.py  ──▶  { patterns: [ [track, …], … ] }   (parse / decode)
    ▲                                          │
    │                                          ▼
 midi_to_t1.py  ◀── .mid files          t1_to_midi.py ──▶ .mid files  (import / export)
    │                                          ▲
    └────────── rebuilds a device-loadable backup zip ──────────────┘

What's decoded (see FORMAT.md for the full byte-map):

• Container layout — bank header, sparse 803-byte track blocks, pattern gaps, trailer, and the two ZIP shapes the device restores (full 8-bank backup / fresh single-bank file).
• Per-step gates, absolute pitch (incl. chords via multi-note pitch locks), velocity and sustain (with the device's real value scales), per-step locks (pitch/velocity/length).
• Track routing (MIDI channel/mask), root, scale, division/timing.
• Cycles — up to 16 per track, with per-cycle pitch/param/step-sequence overrides.
• Steps up to 64, sparse track positions (fixed slots with gaps), and the drum-kit layout.
• Backup-1 parameters — Tempo, per-track Length, Probability, Timing (swing) + subdivision, Delay, Quantize, and the free/fixed-division flag.

The format has no checksum (proven by successful on-device import), which is what makes faithful rebuilding possible.

Repository layout

Requirements

Python 3, no third-party dependencies. (MIDI reading/writing and ZIP handling use the standard library only.) A real T-1 is only needed if you want to load results onto hardware.

Usage

Inspect a bank

python3 t1_format.py samples/09_perstep_polyphony/bank.t1

Prints the decoded tracks, per-step locks, cycles, and each track's slot position.

Export .t1 → MIDI

python3 t1_to_midi.py FILE.t1 -o OUTDIR [--bpm 120]

Writes one Type-1 .mid per non-empty pattern at 96 PPQN (the device's resolution). Without --bpm it uses the bank's stored tempo. Exports gates, per-track division/timing, track pitch + chords, per-step pitch/velocity/sustain locks, multi-channel routing, root and scale.

Import MIDI → .t1

python3 midi_to_t1.py -o OUT.t1 IN1.mid [IN2.mid …] [options]

Each .mid becomes one pattern; each MIDI channel (or SMF track, with --split-tracks) becomes one track. Chords and pitch changes become pitch locks; per-step velocity / note-length become groove locks. Notes are quantized to the step grid (max 16 patterns × 16 tracks).

Common options:

Two placement helpers: --by-filename derives placement from names like pattern1_track2.mid, and --plan FILE.json gives an explicit per-pattern/per-track table (the most general form).

Cycles view

python3 t1_cycles.py FILE.t1

Prints per-track cycle count, step-group page, per-cycle track-pitch overrides, and per-cycle step-sequence records (gate + per-step locks).

Loading results onto the T-1

The device restores a backup ZIP via its Backup menu. Two shapes work (both emitted by the importer — no manual zipping):

• Fresh single-bank file (--new-backup --slot N) — restoring it overwrites only that one bank and leaves the other 7 intact. This is the truly non-destructive path.
• Spliced full backup (--zip REAL_BACKUP.zip --slot N) — replaces one slot inside a real backup you exported; the other banks and settings stay byte-identical.

Every entry must be ZIP_STORED (uncompressed) with the exact ./-prefixed layout the device expects; the tooling handles this. See CLAUDE.md / FORMAT.md for the exact recipe and rules.

⚠️ Back up your device first. These are unofficial, reverse-engineered tools. A malformed bank is rejected by the device (and can trigger a bank re-initialization), so always keep a known-good backup and prefer the single-bank path while experimenting.

Verifying

python3 test_roundtrip.py     # expect: ALL PASS

Rebuilds every archived sample bank byte-for-byte — run it after any change to the parser or to block/container synthesis. Beyond this, synthesized banks (chords, velocity/sustain, cycles, and drum-split kits) have been loaded and confirmed on real T-1 hardware; the working set lives in hwtest/, with device-authored ground-truth references in hwtest/fromT1/.

Status & scope

The musically meaningful format is decoded and hardware-verified in both directions. Remaining work is polish and edge decoding — e.g. exact tick units for Timing/Delay, MIDI→scale/root mapping (currently Chromatic/C so absolute pitch plays), and a few interior bytes of the CC-encoder and modulation records. See CLAUDE.md and decode/ for the current frontier.

License

MIT © 2026 Sebastian Hasinger.

Torso® and T-1 are trademarks of Torso Electronics. This is an independent, unofficial reverse-engineering project and is not affiliated with or endorsed by Torso Electronics.