Future Composer JS

1. Overview

Future Composer JS is a browser-based editor and player for Atari 8-bit Future Composer music files. It supports loading, playing, and editing .FC, .BIN, and .SAP files, and can export edited songs back to the uncompressed .FC format.

The player is an accurate JavaScript port of the original 6502 Future Composer player, using MAME-accurate POKEY chip emulation. No installation is required — open fc_app.html in any modern browser.

2. Screen Layout

The screen is divided into four panels. The active panel is highlighted with a bright border. Press Tab to cycle between panels.

3. Loading Files

Drag and drop a .FC, .BIN, or .SAP file onto the drop zone at the bottom of the screen, or click it to open a file browser.

After loading, the editor populates all four panels with the song data and begins playback automatically.

4. Transport Controls

5. Global Keyboard Shortcuts

The current octave, instrument number, and duration index are always shown in the status bar at the top.

6. Track Editor

The Track Editor shows the song sequence across 3 channels. Each row contains pattern numbers (hex) for channels 1, 2, and 3. Special markers control looping, ending, transposition, and AUDCTL.

Track Byte Values

Track Editor Keys

7. Pattern Editor

The Pattern Editor shows the contents of one pattern (0–63). A pattern is a sequence of commands: instrument selects, duration sets, and notes, terminated by FF (end of pattern).

Pattern Byte Values

Pattern Editor Keys

7.1 Note Entry — Piano Keyboard Layout

Notes are entered using the PC keyboard as a piano. Two rows cover two octaves at a time (controlled by the current octave setting F1–F4).

  Lower row (current octave):          Upper row (octave+1):

  Black keys:  S  D     G  H  J        2  3     5  6  7
  White keys: Z  X  C  V  B  N  M     Q  W  E  R  T  Y  U

  Z=C  S=C#  X=D  D=D#  C=E  V=F  G=F#  B=G  H=G#  N=A  J=A#  M=B
  Q=C  2=C#  W=D  3=D#  E=E  R=F  5=F#  T=G  6=G#  Y=A  7=A#  U=B
  (one octave higher)

The current octave is shown in the status bar. Each note press inserts the note byte and advances the cursor. The current instrument and duration are automatically prepended if they differ from the previous values in the pattern.

Note Name Reference

8. Instrument Editor

The Instrument Editor shows 4 parameters for the currently selected instrument (0–31).

Instrument Editor Keys

9. Envelope Editor

The Envelope Editor shows the byte sequence for the currently selected envelope (0–31). Each byte controls the POKEY AUDCx register for one frame.

Envelope Byte Values

Envelope Editor Keys

10. Export & Save

Click the SAVE button (or press Ctrl+S) to export the current song as an uncompressed .FC file. The file will be downloaded to your browser's download folder.

The exported .FC file can be loaded back into the editor, played in any FC-compatible player, or compiled with the original Future Composer tool on the Atari.

FC File Structure (Exported)

11. FC Format Reference

Duration Table

The duration table has 32 entries. Entry 0 holds the tempo value. Entry n = (n+1) × tempo frames. A tempo of 6 gives durations: 6, 12, 18, 24, ... frames per note.

In patterns, duration bytes are 40–7F: the index is byte & 0x1F (0–31).

Transposition

Transposition is stored as a raw unsigned value 0–15. The default is 8 (written as track byte 88). The note frequency is looked up at index note + transpose. Because the frequency table has 8 unused entries at the start, transpose=8 means "no transposition" into the musical range.

Transpose values: 80=transpose 0 (shift down 8), 88=transpose 8 (default/no shift), 8F=transpose 15 (shift up 7).

Instrument Effect (byte 3)

12. POKEY Channel Mapping

Future Composer uses 3 logical channels mapped to 4 POKEY hardware channels:

Default AUDCTL = $50 (CH1_HICLK + CH12_JOINED). Channel 0 (bass) always uses the 16-bit joined mode for extended low-frequency range. The bass AUDC output is on AUDC1 (CHAN2), not AUDC0.

13. Tips & Tricks

Starting a New Song

1. Click NEW to create a blank song with default settings.
2. Go to the Envelope editor (Tab × 3) and create an attack-decay envelope for instrument 0. Try: 0F 0E 0C 0A 08 06 04 02 FF.
3. Go to the Pattern editor (Tab). Press F2 to set octave 2.
4. Type notes with the piano keys (Z=C, X=D, C=E, V=F, B=G, N=A, M=B).
5. Press Space to hear playback.

Copying Patterns

To reuse a pattern on multiple channels: in the Track Editor, simply enter the same pattern number on different channels at the desired rows.

Percussion

For a percussion hit on a melody channel (Ch 1 or Ch 2): create an instrument with Distort C0 (white noise). In the envelope, use direct bytes (80–FE) for the initial click, then volume bytes for decay. Example: AF 8F 0C 09 06 03 01 FF.

Bass Lines

Channel 0 is always the bass channel (16-bit POKEY mode). Use it for low, sustained notes. Notes N00–N07 (indices below 8) are in the sub-audible range and are shown as N00–N07 in the pattern display.

Speed Control

The tempo is set in the duration table. Shorter duration values = faster notes. Duration index 0 = 1×tempo frames, index 1 = 2×tempo frames, etc. A typical FC song uses tempo 6, giving durations of 6, 12, 18 frames per note.

Vibrato vs. Slide

• Table vibrato (Effect 01–7F): subtle ±1 semitone pitch wobble. The vibrato phase is shared across note re-triggers, so it sounds continuous.
• Continuous slide (Effect 80–FF): the pitch slides upward continuously. Good for risers, sirens, or lead sounds. The slide stops when AUDF reaches $FF.

Keyboard Quick Reference Card

GLOBAL
  Tab         Cycle panel focus (Track → Pattern → Inst → Env)
  Space       Play / Stop
  Esc         Stop
  F1–F4       Set octave 1–4

TRACK EDITOR
  ↑↓←→        Navigate rows / channels
  0–F         Enter pattern number (2 hex digits)
  Shift+0–F   Enter transpose byte (80–8F)
  L           Insert loop (FF)
  E           Insert end (FE)
  Enter       Jump to pattern under cursor
  Ins/Del     Insert / delete row
  +/-         Increment / decrement pattern number

PATTERN EDITOR
  ↑↓          Navigate rows
  Z S X D C V G B H N J M   Notes (lower octave)
  Q 2 W 3 E R 5 T 6 Y 7 U   Notes (upper octave)
  Ctrl+0–9    Set duration index
  Shift+0–V   Select instrument (0–31)
  +/-         Next / previous pattern
  Ins/Del     Insert / delete byte
  Backspace   Set FF (end)
  0–F         Direct hex entry

INSTRUMENT EDITOR
  ↑↓          Select field
  ←→          Decrement / increment value
  0–F         Hex entry (2 digits)
  +/-         Next / previous instrument

ENVELOPE EDITOR
  ↑↓          Navigate rows
  ←→          Decrement / increment byte
  0–F         Hex entry (2 digits)
  +/-         Next / previous envelope
  Ins/Del     Insert / delete byte
  Backspace   Set FF (end)