MagSID

A tracker for writing Commodore 64 music, on Windows, macOS and Linux, and the SID player that plays it on real hardware.

By Magnar Harestad of Censor Design. A big thanks and shoutout to my fellow Censor Design members: Krikkit, Slaygon, Bob and Swallow for design inspirations, technical advices, tools & SVN repo + infrastructure.

Website and download: magnarharestad.github.io/MagSID

What this is

A tracker that edits songs as plain text and exports them as .sid files, reproducing the C64 player exactly — note for note, byte for byte. A song sounds in the editor as it will on the machine, and the exported file is the same image the assembly player would have produced.

The player is a low-memory-footprint rewrite of a GoatTracker-style player, written in c6510 assembly: 418 bytes of code with neither optional effect, 500 with vibrato, 467 with slides and 526 with both, plus 10 bytes when an instrument uses soft hard restart and 4 when two or more instruments in a song with vibrato have none - which is what lets its tables, two bytes an instrument, cover only those that do, and 24 when a pattern changes the speed with an Fxy row, 22 beside slides. Code for an effect is only assembled when a song uses it. A finished song lands at roughly 700–1150 bytes including the player.

Using the editor

Requirements

• Windows 10 or 11 (64-bit), macOS (Apple Silicon or Intel), or Linux on x64
• Nothing to install besides: .NET is built into each download

Nothing else: no assembler, no emulator. Export to .sid and playing a .sid back are built in.

Installing

Unpack the download anywhere and run MagSID.exe on Windows, MagSID.app on a Mac (moved to Applications) or ./MagSID on Linux. There is no installer.

The Windows exe is not code-signed, so Windows SmartScreen may say it comes from an unknown publisher. Choose More info → Run anyway. The Mac app is not notarised yet; the website says how to open it the first time.

Settings — MIDI device, knob bindings, view preferences — are kept in settings.json under MagSid.Editor in the user's application data folder (%APPDATA% on Windows).

Until 1.64 MagSID was a Windows-only WinForms editor; from 1.7 it is one Avalonia editor on every system. 1.64's settings carry over.

Getting started

• Songs are plain-text .s files. Open one from SongData with Menu → Open (F10).
• There are two views of the same song: Retro, a classic tracker grid, and DAW, an arrangement with a piano roll and an instrument page. The menu bar switches between them. In the DAW's arrangement, the tools next to the tabs drag clips between channels, erase, split and glue them.
• F1 plays from the top, F2 from the cursor (in the DAW, from the project cursor), F4 stops. Space or F5 switches between Edit and Jam mode — Menu → Swap Spacebar Behavior gives Space the transport instead.
• A MIDI keyboard is chosen under MIDI. The computer keyboard plays notes too, the classic tracker way: ZSXDCVGBHNJM is one octave and Q2W3ER5T6Y7U the next.
• Menu → Export (F9) writes a PSID .sid, a .prg or raw .bin to use in your own code, at the load address and zero page start you choose, or the Musicshower as a .prg or .d64: a program that plays the song on a real C64 and shows the player's values on screen. Menu → Load and Play .sid plays a .sid, and exports it as WAV, MP3 or FLAC.
• Menu → Import MIDI makes a new song from a .mid file: bass and drums on channel 1, the chords as arpeggio instruments on channel 2, the lead on channel 3, and each part's General MIDI sound mapped to an instrument from the demo songs. midifiles/ has 14 free tunes to try it on.
• The sound bank holds 25 sounds from the demo songs - instruments, drums and arpeggios at three speeds. In the DAW, SOUNDBANK on the instrument page shows them as cards: click one to hear it, double-click or + to add it. In Retro it is under the instrument list's ▾ menu.

Menu → About lists every key and control, view by view.

Layout

MagSid.sln
src/
  MagSid.Core/            the song model, file format, sizing, undo, optimiser
  MagSid.Sid/             a reSID port - the chip itself
  MagSid.Playback/        voices, sequencer, jam mode, filter, the .sid player
  MagSid.Assembler/       the .sid export: a 6502 emitter and the player expressed against it
  MagSid.Editor.Avalonia/ the editor, on Windows, macOS and Linux
  MagSid.Editor.Views/    the tracker grid and DAW views, compiled against Shim/ - WinForms and GDI+
                          over Avalonia
  MagSid.Editor.Common/   settings, session, .sid export - shared by both editors
  MagSid.Editor.App/      the WinForms editor (to 1.64): the source of the grid and DAW views
  MagSid.Audio.PortAudio/ sound out on every system
  MagSid.Midi/            MIDI in: WinMM, CoreMIDI, ALSA
tests/
SongData/                 the songs, as plain text
Digi/                     a sample for the Digi-to-SID-osc feature
midifiles/                14 public-domain and Creative Commons tunes for Import MIDI
website-messages/         the website's message wall: a Cloudflare Worker, see its README

The three ports, and what keeps them honest

Three pieces of C# each mirror something in the assembly player, and all three would drift silently if nothing checked them. So each is pinned to real assembler output rather than reviewed:

• MagSid.Playback.SongSequencer mirrors Code/musicplayer.s — this is what makes in-editor playback match the machine.
• MagSid.Core.SongSizeCalculator mirrors the Lua emitter in Startup/Tables.s. Its byte counts are pinned against real c6510 builds in SongSizeTests, which has caught song edits three times and a renamed file once.
• MagSid.Assembler produces the exported image: a byte emitter with labels, a line-for-line port of the player, and five emitters mirroring the tables Tables.s generates. 34 mnemonics in 7 addressing modes is all the player uses, which is small enough to emit directly.

Playing the exported file back is a separate answer to a separate question. MagSid.Playback carries a 6502 interpreter and a PSID loader, so the editor plays a .sid by executing it — SidFilePlaybackTests then checks that those bytes, run on the CPU, write the same SID registers as SongSequencer over 1500 frames of every song. Goldens prove the export is the right bytes; this proves those bytes make the right music. Neither alone would.

SongImageTests compares the complete image — player and song data — against what c6510 produced, for seven songs and for BellaCiao at $2000 and $4400. Two fixture songs come with it because those seven reach only two of the four feature combinations: six are bare and BellaCiao has vibrato. Songs written since — Clarity, Outlaws and Fairlighty, which use vibrato, slides and soft hard restart — are checked by running their image on the 6502 against SongSequencer, frame by frame.

Comparing whole images and not just their lengths is the point. Reversing the note dictionary's build order — arpeggios before pattern rows — yields an image of exactly the right length with every note wrong, and the length cross-checks stay green through it. Only the byte comparison catches that, and it is the failure mode that would ship.

Those reference images are frozen in tests/MagSid.Assembler.Tests/Goldens/, captured while the assembler was still in this repository. See the README beside them before changing one.

Building

Needs the .NET 8 SDK. Nothing else — no assembler, no include library, no player sources.

dotnet build MagSid.sln
dotnet test MagSid.sln

A tag v1.7 makes .github/workflows/release.yml build the packages for every system - the Mac app for Apple Silicon and Intel, Windows and Linux, each with .NET inside - and open a draft release with them. packaging/portable/package.sh and packaging/macos/package.sh do the same by hand.

Measuring how smoothly it draws. Set MAGSID_FRAMEPROBE to a log file and open a song, and the editor plays it silently, measures 1500 displayed frames and closes. The log has the frame gaps, each view's paint times, the garbage collections and the largest allocations. MAGSID_FRAMEPROBE_DAW=1 measures the DAW view instead of the Retro view. Check both after any change to how either draws.

MAGSID_FRAMEPROBE=retro.txt MagSID "SongData/MysData2026 - Clarity.s"
MAGSID_FRAMEPROBE=daw.txt MAGSID_FRAMEPROBE_DAW=1 MagSID "SongData/MysData2026 - Clarity.s"

Optional

The player sources, if you want to assemble the C64 side or regenerate a golden. The c6510 source is in the Censor SVN tree under MAGSIDv7_LowMemory as it stood at commit 6221867, together with the c6510 assembler, its include library, and the Python tools that measure byte cost and trace a player's register writes. Every change made to the player since — pattern slides, soft hard restart, and a note off that lets the release run on — is in tests/MagSid.Assembler.Tests/Goldens/player.patch, against that version.

License

Exported .sid files - the player code and the song data in them - may be used freely, in any release, commercial or not.

MagSID Editor is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 2 of the License, or (at your option) any later version. It is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See LICENSE for the full text.

The editor's SID emulation is a C# translation of reSID by Dag Lem, which is licensed under the GPL, version 2 or later - so the editor is too. It also includes NAudio, under the MIT license. Both are credited in THIRD-PARTY-NOTICES.md.

The MIDI files in midifiles/ are not part of the program and keep their own licences - public domain or Creative Commons - listed with credits in midifiles/README.md.