Intellivision Overlay Editor

① The Big Picture

The Intellivision uses a chip called the STIC (Standard Television Interface Circuit) to draw graphics. It can display two types of visuals at the same time:

② GRAM — Your Art Canvas

GRAM (Graphics RAM) is a bank of 64 custom 8×8 pixel cards, numbered 0 – 63. You draw your pixel art here and then reference these cards from tiles or MOBs. The 64-slot budget grid in the editor shows you exactly which slots you've used.

③ Drawing Pixels — BITMAP

In IntyBASIC, each row of pixels is one BITMAP line with 8 characters:

• X — foreground pixel (shows the sprite's color)
• . — background pixel (transparent on MOBs; background color on tiles)

player:
    BITMAP "..XXXX.."   ' row 0 — top of head
    BITMAP ".XXXXXX."   ' row 1
    BITMAP "XX....XX"   ' row 2
    BITMAP "XXXXXXXX"   ' row 3
    BITMAP "XX....XX"   ' row 4
    BITMAP ".XXXXXX."   ' row 5
    BITMAP "..XXXX.."   ' row 6
    BITMAP "........"   ' row 7 — empty

The Sprite Editor generates this code for you automatically. You just draw with your mouse!

④ Loading Art into GRAM — DEFINE

Before the STIC can display your sprite, you must copy it from your program's data into GRAM:

DEFINE slot, numCards, label

DEFINE 0, 1, player     ' copy player into slot 0  (one 8×8 card)
DEFINE 5, 2, tall_guy   ' copy tall_guy into slots 5–6 (two cards = 8×16)
DEFINE 10, 4, boss      ' copy boss into slots 10–13 (four cards = 16×16)

The editor writes the correct DEFINE line for you in the output panel, using the GRAM Slot you assign in the properties panel.

⑤ The 3 Use Modes

SPRITE n, (x + $200), y, (slot * 8 + color)

' Example: MOB 0 at (50,60), slot 2, White
SPRITE 0, (50 + $200), 60, (2 * 8 + 7)

BACKTAB(row, col) = fgColor + slot * 8 + $800

' Slot 3, foreground = Green (5)
BACKTAB(2, 4) = 5 + 3 * 8 + $800

BACKTAB(row, col) = slot * 8 + $C00

' Set per-row color registers before drawing
' $C00 = GRAM flag ($800) + FG/BG mode flag ($400)

⑥ Wide & Tall Sprites — Using Multiple Cards

⑦ The 16 Intellivision Colors

MOBs and Color Stack tiles use colors 0–7 (primary). FG/BG tiles and backgrounds can also use 8–15 (pastel/extended).

⑧ Hello World — Your First Sprite

Here's the minimal IntyBASIC code to put a white box on screen as a MOB:

' 1. Define the BITMAP data
box:
    BITMAP "XXXXXXXX"
    BITMAP "X......X"
    BITMAP "X......X"
    BITMAP "X......X"
    BITMAP "X......X"
    BITMAP "X......X"
    BITMAP "X......X"
    BITMAP "XXXXXXXX"

' 2. Load into GRAM slot 0
DEFINE 0, 1, box

' 3. Place MOB 0 at screen position (50, 50), White (color 7)
SPRITE 0, (50 + $200), 50, (0 * 8 + 7)

' 4. Start the game loop
DO
    WAIT        ' wait for video frame
LOOP

⑨ Recommended Workflow

1. Choose a size — 8×8 for simple sprites, 8×16 for taller characters, 16×16 for large bosses.
2. Draw your pixel art — Left-click to draw foreground pixels; right-click to erase.
3. Assign a GRAM slot — Enter a slot number in the Sprite Properties panel. Check the GRAM budget grid to avoid conflicts.
4. Pick a Use Mode — MOB for moving objects, Color Stack for background tiles, FG/BG for tiles needing two distinct colors.
5. Set the color — Choose the MOB color or tile foreground color in the properties panel.
6. Copy the output — Click Copy Bitmap or use the Output panel. Paste into your .bas file.
7. Add more sprites — Use Add in the Sprites panel. Each gets its own GRAM slot automatically.
8. Save your work — Export Project saves a .json file you can reload later.

⑩ Reconstruct Screens from a Live Game

The Sprite Editor and Layout Designer can import memory dumps from jzIntv's debugger to rebuild any screen of any Intellivision game — your own work, a homebrew, or a commercial title.

What you need:

• jzIntv launched with the -d flag (debugger enabled)
• Any Intellivision ROM running to the screen you want to capture
• Press F4 in the game window to break into the debugger (or Ctrl+C in the terminal)

Step 1 — Capture GRAM: At the debugger prompt, run m 3800 200. Copy the output (lines starting 3800:), then in the Sprite Editor toolbar click 📥 Paste GRAM and paste. Every non-empty GRAM card becomes an editable 8×8 sprite at its original GRAM slot.

Step 2 — Capture BACKTAB: At the same break point, run m 200 F0. Copy the output. Open 🖥️ Layout View, click 📥 Paste BACKTAB, and paste. The full 20×12 screen reconstructs:

• GRAM tiles render with the pixel art you imported in Step 1
• GROM tiles (the Intellivision's built-in character set) show as gray G<n> placeholders so the layout structure is always visible
• Per-cell foreground and background colors are decoded for both Color Stack and FG/BG STIC modes

Tip: take both dumps at the same break point. The GRAM and BACKTAB need to match — if the game animates between dumps, the BACKTAB may reference card numbers that don't exist yet in your imported GRAM.

Feature suggested by Steve Ettinger, original Mattel Electronics Intellivision programming team.

① The Sound Chip — AY-3-8914 PSG

The Intellivision uses a Programmable Sound Generator (PSG) chip that provides:

• 3 melody channels — each produces a square wave at a programmable frequency. They're completely independent: different notes, different octaves, different instruments.
• 1 noise channel — generates white noise for percussion. IntyBASIC maps drums (M1/M2/M3) to this channel automatically.

With the ECS expansion, a second PSG is available — doubling you to 8 channels (6 melody + 2 drum). Click + ECS in the channel toolbar to enable it, or load an 8-arg MUSIC song and it auto-detects. The piano-roll grows a second drum strip (top = ECS) and channels 4–6 paint in cyan / yellow-green / tan.

② The 4 Instruments — W, X, Y, Z

IntyBASIC shapes each note with an envelope — how the volume rises, holds, and fades. The four letters select different shapes:

Once you set an instrument on a channel (e.g. C4X), it carries over for all subsequent notes on that channel until you change it.

③ Drums — M1, M2, M3

The 4th argument of each MUSIC statement controls the noise/percussion channel:

• M1 — Strong: Low-frequency noise burst filtered through a lowpass → a "kick drum" thud. Use on beats 1 and 3.
• M2 — Tap: Short high-frequency noise snap → a "snare" click. Use on beats 2 and 4 (backbeat).
• M3 — Roll: Medium-frequency shimmering noise → a "hi-hat" sizzle. Use on every tick for a steady rhythm pulse.
• - — Silence. No drum this tick.

A basic rock beat at 16 ticks per bar: M1 M3 M3 M3 | M2 M3 M3 M3 | M1 M3 M3 M3 | M2 M3 M3 M3

④ Tempo — DATA & Ticks

IntyBASIC's music engine runs at 50 ticks per second (on both NTSC and PAL). The DATA value at the top of your song sets how many ticks each MUSIC line lasts:

• DATA 6 → 50/6 ≈ 8.3 notes/sec → ~125 BPM (fast, driving)
• DATA 8 → 50/8 = 6.25 notes/sec → ~94 BPM (moderate)
• DATA 10 → 50/10 = 5 notes/sec → ~75 BPM (slow, atmospheric)

You can change tempo mid-song with MUSIC SPEED <n>.

⑤ Notes & Octave Range

Notes are written as letter + octave, optionally with # for sharp and an instrument letter:

C4   D4#   E3Z   A5X   G2   B4#Y   F4W

The PSG's usable range is C2 (low rumble) to C7 (thin squeak). The sweet spot for melodies is C3–C6. Bass lines with Z instrument work best at C2–C3 (they'll sound an octave lower due to the Z drop).

S (sustain) = hold the previous note. - = silence.

⑥ Song Structure — Looping

Most Intellivision songs use the intro + loop pattern:

MySong:
  DATA 6
  MUSIC E4X, E2Z, -, M1     ' intro bar
  MUSIC G4X, S,   -, M3
  ...

MySong_loop:
  MUSIC C4X, C3Z, -, M1     ' main body starts here
  MUSIC E4X, S,   -, M3
  ...
  MUSIC JUMP MySong_loop     ' loops back forever

MUSIC JUMP <label> loops back to a label. MUSIC REPEAT loops the entire song. MUSIC STOP ends playback. The Music Studio's 🔁 Loop button plays the loop body multiple times so you can listen continuously.

⑦ Hardware Hazard — DOSOUND clobbers $011E

Tip from Steve Ettinger, legendary Intellivision developer:

If you (or anyone) is using the Exec DOSOUND routine, there is a RAM address ($011E) in user RAM that gets overwritten indiscriminately by the DOSOUND — BEWARE when coding your own game to be SURE that you burn that location with a dummy RAM variable so that your game won't be tanked by DOSOUND!

What this means for you:

• The Music Studio is unaffected. IntyBASIC's MUSIC engine writes the PSG registers directly — it does not route through DOSOUND. Songs exported from this editor are safe.
• If your game also uses SOUND statements (which compile down to DOSOUND-style PSG writes), reserve $011E with a dummy variable so the EXEC's sound routine doesn't silently corrupt whatever else you stored there.
• Watch out for this if you ever see a variable mysteriously changing during gameplay while sound effects play — $011E is the prime suspect.

⑧ Shortcuts & Gestures

Everything you can do without leaving the keyboard:

All keyboard shortcuts only fire while the Music tab is active and you're not typing in a text field.

⑨ Quick Start — Your First Song

1. Click ➕ New Song to start with a blank canvas.
2. Select Channel 1 and Instrument X (clarinet) in the edit controls.
3. Click notes on the piano-roll to place a melody. Start simple — C4, E4, G4, C5 is a C major arpeggio.
4. Switch to Channel 2, select Instrument Z (bass). Click lower notes (C2, G2) to add a bass line.
5. Switch to Drums. Click in the bottom purple strip to add M1 kicks and M3 hats.
6. Press ▶ Play to hear it. Adjust volume with the 🔊 slider.
7. 📄 Copy Source gives you the IntyBASIC MUSIC statements to paste into your game's .bas file.

⑩ Music Engines & Credits

The Music Studio supports multiple native Intellivision music engines, each created by community authors. Their work made this editor possible — please credit them when sharing songs:

• IntyBASIC MUSIC (base PSG + ECS 8-channel) — by Oscar Toledo G. (nanochess). The native MUSIC/PLAY system shipped with the IntyBASIC compiler. nanochess.org/intybasic ↗
• Chevallier Tracker — by Arnauld Chevallier (2008). The original 3-channel assembly tracker used in Joe Zbiciak's Space Patrol and other homebrew titles. Intellivision Wiki ↗
• IMT — Intellivision Music Tracker — extended by James Pujals (DZ-Jay), building on Chevallier's original. v1.5 adds 6-channel ECS support, first-class envelope instruments, multi-step drum samples, and pitch effects. AtariAge thread ↗
• ZMUS — by Joe Zbiciak. A microprogrammed bytecode music engine that lives at $D000; well-suited to JLP-equipped cartridges. See lib/zmus_engine.bas in the intv-game-builder collection ↗.

Demo songs in the editor: the Space Intruders soundtrack (IntyBASIC) and the ECS Hex Choir showcase composed for this editor. Both source files are bundled in the intv-game-builder collection ↗.

① The Sound Chip — A Quick Recap

The Intellivision's AY-3-8914 PSG (Programmable Sound Generator) is the same chip that drives music — see the 📖 Audio Primer on the Music Studio tab for the full architecture. The fast recap:

• 3 tone channels (A, B, C) — each plays a square wave at a programmable period (12-bit, 1–4095). Frequency ≈ 894886 / (16 × period) Hz.
• 1 noise generator — white noise at a 5-bit period (0–31). Lower period = brighter / hissier; higher period = deeper rumble.
• 1 hardware envelope generator — shapes the volume of any channel routed through it. 16 selectable shapes, settable cycle period.
• 1 mixer register — chooses, per channel, whether tone, noise, or both reach the output.

Music uses the same chip, the same channels, the same registers. SFX has to coexist with music — so dedicating one channel to SFX (conventionally channel C) lets the music engine keep A and B for melody.

② Three Ways to Make Noise in IntyBASIC

③ The Four Ingredients of a PSG Sound Effect

Every preset in the SFX Lab is built from four ingredients. Tweaking them in combination is the whole game:

• Channel (A / B / C) — which tone generator owns this effect. Channel C is the conventional SFX slot because it leaves A and B free for music.
• Frequency + how it changes (the sweep). A held tone is rare; most effects sweep from one pitch to another. Sweep shape (step / linear / exp / quadratic) is the defining "character" knob.
• Noise — on or off, plus a period that controls timbre. Noise without tone = explosions, wind, percussion. Tone with noise mixed in = raspy lasers, missile thrusters.
• Envelope — how the volume changes over time. Manual = linear fade per step. HW envelope = the AY's built-in shape generator (16 options).

Six of the SFX Lab's presets are multi-phase — they chain several different "ingredient settings" end-to-end (see section ⑦). Most one-shot SFX work fine with a single phase.

④ Sweep Shapes — The Character of an Effect

The Sweep dropdown in the Designer chooses how the tone moves from Freq start to Freq end across the segment's steps:

Steps controls how many sample points the sweep lands on. More steps = smoother sweep, more SOUND writes, more bytes. 5–12 covers most SFX; 20+ is reserved for long held effects.

⑤ The Noise Channel — Texture & Period

The PSG noise generator outputs pseudo-random white noise. One 5-bit period register (SOUND 6, range 0–31) controls timbre — and only timbre. Volume is set per-channel via the volume register, and what reaches the output is governed by the mixer.

• Period 1–4 — bright crackle, almost TV-static. Glass shatter, electric fizzle, snare snap.
• Period 6–12 — general-purpose explosion / boom. Most arcade explosions land here.
• Period 14–22 — mid-deep, broadband texture. Whoosh, wind, distant thunder.
• Period 24–31 — sub-bass rumble. Earthquakes, big-bomb shockwaves.

The Noise Period slider in the Designer sets the starting period. Multi-phase presets sweep period across phases — Astrosmash's classic boom sweeps 14 → 24 over 22 frames, giving the texture-deepening signature.

Mixing tone + noise (turn on Noise and have non-zero freq) is how you get raspy lasers, throaty missile thrusters, gravelly hurts. Pure noise = percussion. Pure tone = clean pitch effects. Mix = textured.

⑥ Envelopes — Manual vs Hardware

The volume curve over time is what separates a "tweet" from a "splat." The SFX Lab supports two modes via the Envelope Mode dropdown:

The four Ambience presets (Helicopter, Siren, Seawaves, Saucer Drone) all use HW envelope to loop a shaped volume curve without burning CPU per frame. Open one and inspect the IntyBASIC output to see the SOUND 11/12/13 setup pattern.

⑦ Multi-Phase Effects — Chaining Configurations

Complex SFX (Plasma Cannon, Boss Reactor Meltdown, Belt-Buckle Powerup) can't be expressed as a single freq sweep — they chain multiple PSG configurations end-to-end. The SFX Lab represents this as a segments array where each segment has its own freq, noise, volume, and duration fraction.

Examples in the library:

• Belt-Buckle Powerup (2 phases): metallic noise snap → descending tonal ring.
• Plasma Cannon (3 phases): bass thrum → mid arc → deep rumble tail.
• Boss Reactor Meltdown (4 phases): rising alarm → noise chaos → bass+noise sustain → aftershock pulses.
• Stepped Fanfare (4 phases): four ascending tones (each a held pitch for a quarter of the total duration) — the level-up sting pattern.
• Saucer Drone (looping, 2 phases): alternating two-tone hum that loops until stopped.

Multi-phase presets show a JSON view in the Designer instead of flat sliders — per-phase slider editing is on the v2 roadmap. The preview and the IntyBASIC output both fully reflect the design; only the in-place editing is deferred.

⑧ EXEC ROM Sound Routines — Mattel's Pre-Baked SFX

Every Intellivision boots from Mattel's 4KB EXEC ROM — the same binary on every console, every cartridge. It contains a set of canonical sound routines you can call from IntyBASIC via ASM CALL $XXXX:

Source of truth: jzIntv's disassembler symbol table (dasm/exec_interp.c).

Why they matter: Crowd cheer / groan are sample-quality compared to anything you can write with SOUND directly — they're the difference between a generic arcade bleep and "the crowd reacted." The SFX Lab's EXEC tail dropdown appends one of these calls after the PSG effect, giving you instant access to compose patterns like a descending PSG tone fading into a crowd groan (see the Letdown preset). The PSG → EXEC composition pattern itself is a contribution from Steve Ettinger — see §⑪.

The Web Audio preview only approximates the EXEC routines (since the actual byte sequences live in Mattel's copyrighted ROM and aren't reproduced here). The exported IntyBASIC calls the real ROM at runtime, so what you ship sounds correct.

⑨ Hardware Hazard — DOSOUND Clobbers $011E

Tip from Steve Ettinger, legendary Intellivision developer:

If you (or anyone) is using the Exec DOSOUND routine, there is a RAM address ($011E) in user RAM that gets overwritten indiscriminately by the DOSOUND — BEWARE when coding your own game to be SURE that you burn that location with a dummy RAM variable so that your game won't be tanked by DOSOUND!

What this means for the SFX Lab:

• The Lab's generated SOUND writes are direct PSG register writes, not DOSOUND bytecode — so the SFX statements the Lab produces don't touch $011E themselves.
• However, the EXEC sound routines (CROWD, RAZZ, etc.) do route through DOSOUND internally. If you use the EXEC tail feature, reserve $011E with a dummy variable so EXEC's sound interpreter doesn't silently corrupt whatever your game stored there.
• This is the same warning the Music Studio's Audio Primer carries — it's the most common silent gameplay bug in homebrew titles that mix MUSIC + SOUND + EXEC routines.

⑩ Quick Start — From Preset to .bas

1. Click any preset in the left panel. The Designer loads the patch, the IntyBASIC output updates live, and Web Audio plays the effect immediately.
2. Tweak in the Designer: channel, duration, freq sweep, noise, envelope. Every change re-renders the SOUND output and plays the next preview when you press ▶ Play.
3. (Optional) Add an EXEC tail — e.g. Crowd Groan after the Letdown preset, or Referee Whistle after a foul SFX. The tail plays once at the end and is excluded from any loop.
4. (Optional) Toggle Loop — for ambient SFX like Saucer Drone or Helicopter. The output wraps in a sfx_loop: label + GOTO sfx_loop; remove the GOTO to make it one-shot.
5. 📋 Copy SOUND drops the IntyBASIC statements onto your clipboard. Paste into your .bas file as a labelled subroutine, then GOSUB it whenever the effect should fire.

Showcase presets to demo each capability:

• Astrosmash Boom — the canonical Intellivision death sound (noise period sweep).
• Defender Crack — 80ms ultra-fast laser (linear sweep, max punch).
• Plasma Cannon — 3-phase multi-segment effect (envelope buckets).
• Helicopter — HW envelope shape 12 (sawtooth-up loop) driving the noise channel.
• Letdown ★ — descending PSG tone + EXEC Crowd Groan composition. Showcases the PSG → EXEC tail pattern (see §⑪).
• Cascade — multi-phase noise SFX (4 segments: hit → fade → swell → fade). Good demonstration of the segmented patch model.

⑪ Sources & Credits

The SFX Lab's preset library was distilled from a treasure trove of existing Intellivision sound code. Please credit these authors when you share derived work:

• Oscar Toledo G. (nanochess) — author of the IntyBASIC compiler, the Advanced Programming for the Intellivision book, and the bundled samples/ programs (envelope.bas, lander.bas, pak.bas). The Bird Chirp, Pumpkin Fire (quadratic), and all four Ambience presets descend from his cookbook and envelope demos. nanochess.org/intybasic ↗
• Joe Zbiciak (intvnut) — author of jzIntv (the emulator powering this editor's bit-perfect playback path) and the Space Patrol homebrew. Space Patrol's snd/sfx.asm contributed the clean 2-word "init-record" SFX engine pattern and several looping-ambient ideas. The canonical EXEC ROM addresses in section ⑧ come from jzIntv's disassembler symbol table. spatula-city.org/~im14u2c/intv ↗
• Steve Ettinger — legendary Intellivision developer. Two pieces of advice that shaped the SFX Lab:
  • The $011E DOSOUND hazard warning (§⑨) — his exact quote, used verbatim with permission.
  • The EXEC CROWD composition pattern (§⑧) — pairing a PSG-synthesized SFX with an EXEC ROM routine for sample-quality endings. The Letdown preset is the editor's reference implementation.
• The intv-game-builder collection — Mike's own homebrew & SFX-research workbench, where most of the catalog mining for these presets happened. Source: gitlab.com/mholzinger/intybasic-workbench ↗. Specific contributors to the preset library:
  • Space Intruders (games/space-intruders/) — the unified 15-type UpdateSfx engine in waves.bas contributed Spongey Bwop, Saucer Schwing, Belt-Buckle Powerup, and Saucer Drone.
  • Intruders Beats (games/intrudersbeats/src/sfxlab.bas) — a 27-effect cataloged sound-design ROM. Astrosmash Boom, Defender Crack, SI Missile, Sad Descent, Plasma Cannon, and Boss Reactor Meltdown. The companion intruderexplosions.bas contributed additional explosion patterns.
  • downbeat / boss-test — rhythm-game SFX patterns and boss-assembly stings. The Stepped Fanfare preset distills patterns observed across these projects.

Every preset stores its source attribution in a // Source: comment inside the preset definition in sfxEditor.js — search there to find the originating .bas / .asm file and line for any specific effect.