Manual

GTMobile is a C64 SID tracker for Android. It is based on and largely compatible with GoatTracker 2.

This page describes the controls, in the order they appear in the app. Always-on controls come first, then the project, song, instrument, and settings views. Each section shows the screen and lists what its buttons and gestures do. The last section covers where a GTMobile song differs from a GoatTracker 2 song.

• Always-On Controls
• Project View
• Song View
• Command Editor
• Instrument View
• Instrument Manager View
• Settings View
• Differences from GoatTracker 2

Always-On Controls

These controls stay on screen in every view: tabs and undo/redo at the top, the piano and playback buttons at the bottom.

Tabs

• PROJECT — Opens the project view.
• SONG — Opens the song view.
• INSTR — Opens the instrument editor. Tap again to open the instrument manager.
• Settings — Opens the settings view.
• Undo — Reverts the last song edit.
• Redo — Re-applies an undone edit.

Piano

The piano plays the current instrument on the voice selected in the song view.

• Instrument (left, shows index and name) — Opens the instrument picker. In the song view, long-press this button to set the piano instrument from the selected pattern row (if that row has an instrument).
• Scrollbar — Drag horizontally to scroll which keys are visible.

Instrument Picker

Instruments are numbered 01–3F.

• Tap an instrument to select it and close the picker. Empty instruments (no table pointers) are shaded. Long-press an instrument and drag to reorder instrument slots.
• CLOSE — Closes the window.

Playback

• Fast Backward — Jumps to the start of the current pattern. Tap again to go back one order-list row.
• Stop — Stops playback and sets the restart point to the current order row.
• Play/Pause — Starts playback from the current start position, or pauses if already playing.
• Follow — When on, the pattern view follows playback.
• Loop — When on, playback loops the current pattern instead of advancing in the order list.
• Fast Forward — Skips to the next order-list row.

Project View

The project view is where you name the song and work with song files.

• TITLE — Song title, stored in the song file and in an exported SID.
• AUTHOR — Author name.
• RELEASED — Copyright / release note.
• FILES — Songs saved on the device.
• DEMOS — Bundled demo songs. They can only be loaded.
• File name (FILES) — Name of the current song file. LOAD, SAVE, DELETE, and EXPORT use this name.
• LOAD — Loads the selected file or demo.
• SAVE — Saves under the file name.
• DELETE — Deletes the selected file.
• IMPORT — Imports a song from the system file picker.
• EXPORT — Opens the export window. Disabled until the file name is set.
• RESET — Clears the song.

Export Window

• SNG / SID / WAV / OGG — Export format.
• EXPORT — Writes that format and hands the file to the system share/export flow. WAV and OGG render in the background with a progress bar.
• CLOSE — Closes the window.
• CANCEL — Aborts an in-progress WAV/OGG render.

Song View

The song view has an order list and patterns. Each order-list row says which pattern plays on each of the three SID voices.

Tap an order-list cell to select it (that row’s three patterns appear below). Long-press and drag to select a region of cells.

Order List — One Cell

• Paste — Pastes a copied order-list region starting at this cell.
• Delete Row — Deletes this order row on all voices.
• Add Row Above — Inserts a copy of this row above.
• Add Row Below — Inserts a copy of this row below.
• Loop Here — Marks this row as the loop start when the song repeats. The row shows a small loop mark.
• Clone Pattern — Copies this cell’s pattern into a free pattern slot and points the cell at the copy (only if the source pattern is not empty).
• Edit — Opens the pattern index window for this cell.

Order List — Region

• Copy — Copies the selected order cells.
• Edit — Same as Edit, for every cell in the selection.

Pattern Index Window

Patterns are numbered 00–CF.

• Tap a pattern number to assign it to the selected cell(s). Empty patterns are shaded. Long-press a number and drag to reorder pattern slots.
• TRANSPOSE slider — Sets order-list transpose for the selected cell(s).
• CLOSE — Closes the window.

Pattern Channels

Above the pattern rows, three buttons show the current pattern index per voice. Tap one to mute or unmute that voice. The small bar is the SID envelope level. Drag the handle on the right (between the two scroll bars) to move this split up or down.

Pattern — One Row

Tap a pattern row to select it. Long-press and drag to select a region.

• Paste — Same as Paste, for notes and commands.
• Pattern Length — Opens the pattern length window.
• Delete Row — Shifts later rows up and clears the last row (does not change pattern length).
• Add Row Above — Shifts this row and below down, leaving an empty row here.

Note Tools

• Clear Note — Clears the note and instrument on this row (auto-steps if auto-step is on).
• Gate off/on — Writes a gate-off. Tap again on a gate-off row to write gate-on.
• Record — When on, piano keys write the current instrument’s note into this row (and auto-step).
• Auto-Step — When on, note entry advances the cursor. Long-press opens the auto-step window.

Command Tools

• Clear Command — Clears the pattern command and data.
• Edit Command — Opens the command editor. If the command is a table pointer (wave, pulse, or filter table), long-press jumps to that instrument and table in the instrument view.

Playback From Cursor

• Play From Here — Starts the song at this order row and pattern row.
• Play Row — Plays this pattern row once (and auto-steps).

Pattern Length Window

• LENGTH slider — Sets this pattern’s row count.
• RESIZE EMPTY PATTERNS — Sets every empty pattern to this length.
• SHRINK — Drops every other row (halves length).
• EXPAND — Inserts a blank row after each row (doubles length).
• CLOSE — Closes the window.

Auto-Step Window

• STEP slider — How many rows to advance on note entry (1–8).
• CLOSE — Closes the window.

Pattern — Region

• Copy — Same as Copy, for notes and commands.
• Clear — Clears notes and commands in the region.
• Copy Notes — Copies only notes and instruments.
• Clear Notes — Clears notes and instruments.
• Transpose up / Transpose down — Moves notes in the region by one semitone (clamped to the valid note range).
• Set Instrument — Sets every existing instrument index in the region to the piano’s current instrument.
• Copy Commands — Copies only commands.
• Clear Commands — Clears commands and data.
• Edit Command — Opens the command editor and applies the result to every row in the region.

Command Editor

The command editor opens from a pattern row, a pattern region, or a wave-table command row. Commands are listed on the left. Parameters for the selected command appear on the right. Parameter changes are written as you edit.

• Tap a command name to select it.
• CLOSE — Closes the window.

Some commands are hidden when editing from the wave table.

Portamento

PORTAMENTO UP, PORTAMENTO DOWN, and TONE PORTAMENTO share this layout. Pick a speed-table slot. Slot 00 is OFF, or TIE NOTE for tone portamento.

• PRECALCULATED — Adds or subtracts a fixed amount from the voice frequency each tick. Fine control, but the same amount covers more semitones on low notes than on high notes. HI and LO set that 16-bit amount.
• NOTE-INDEPENDENT — Takes the current note’s pitch, shifts it right, and uses the result as the step, so the rate stays similar on every note. Coarser than precalculated. SHIFT is how many times to shift. Higher is slower.

Vibrato

Same window as portamento: a speed-table slot list, then PRECALCULATED or NOTE-INDEPENDENT. Slot 00 is OFF.

• VIBRATO STEPS — How many steps the pitch travels before turning around. Higher is a wider wobble and a slower cycle.
• SPEED — Size of each step in precalculated mode. Higher is a wider wobble at the same cycle time.
• SHIFT — Size of each step in note-independent mode. Higher is a smaller step.

Attack/Decay & Sustain/Release

ATTACK/DECAY sets the attack and decay nibbles. SUSTAIN/RELEASE is the same layout for the other two.

Wave

Same eight SID flags as the wave table: Noise, Pulse, Saw, Triangle, Test, Ring, Sync, Gate.

Table Pointer

WAVE TABLE, PULSE TABLE, and FILTER TABLE pick an instrument whose table to use, or OFF. This is not a raw table address (see Differences from GoatTracker 2).

Filter Control

• VOICE 1 / VOICE 2 / VOICE 3 — Which voices go through the filter. These are the chip voices, as in the filter table.
• RES — Filter resonance.

Filter Cutoff

Slider for the filter cutoff (00–FF).

Master Volume

Slider for the SID master volume (0–F).

Funk Tempo

Pick a speed-table slot. Slot 00 is NO CHANGE.

• EVEN ROW / ODD ROW — Ticks per pattern row, alternating even and odd rows. Lower is faster.

Tempo

Same unit as funk tempo: ticks per pattern row. Lower is faster.

• THIS VOICE ONLY — Sets tempo only on the voice that runs the command.
• ALL VOICES — Sets the same tempo on all three voices.

Instrument View

Instruments define how a note sounds: volume envelope (ADSR), vibrato, gate timing / hard restart, the first-frame wave, and wave, pulse, and filter tables. Pattern notes pick an instrument by number.

Tap a field above the table to edit it below. Tap a table row to edit that row.

Header

• Index — Instrument number (01–3F). Display only.
• Name — Instrument name.
• / Previous / Next — Selects the previous or next instrument.
• Copy — Copies this instrument, including its table data.
• Paste — Pastes that copy onto the current instrument.
• WAVE / PULSE / FILTER — Selects which table is shown. A shaded tab means this instrument has no table of that type yet.
• Share — Opens the table sharing window. Highlighted when at least two instruments use this table.

ADSR

Tap the ADSR field. Four sliders: ATTACK, DECAY, SUSTAIN, RELEASE.

Vibrato

Tap the vibrato field.

• VIBRATO DELAY — Frames before vibrato starts. 00 disables vibrato.
• STEPS, PRECALCULATED / NOTE-INDEPENDENT, SPEED, and SHIFT — Same meaning as vibrato in the command editor.

Gate Timer

These control the ticks just before a new note starts (gate-off and hard restart). The timer must stay below the current tempo (at most tempo−1). Too high stops playback.

• GATE TIMER — How many ticks before the note that gate-off / hard restart run.
• HARD RESTART — When on, the voice is hard-restarted before the note so it retriggers cleanly (ADSR for that comes from Settings → HARD RESTART). When off, skip hard restart.
• DISABLE GATE — When off, skip the automatic gate-off before the note. With First Wave NO CHANGE, that is the usual legato setup (tables and ADSR still re-init).

First Wave

Waveform written on the note’s init frame. Common choice is gate + test.

• WAVE — Sets that init waveform with the same eight flag buttons as the wave table.
• GATE ON — Leave the waveform unchanged, force gate on.
• GATE OFF — Leave the waveform unchanged, force gate off.
• NO CHANGE — Leave waveform and gate unchanged. With DISABLE GATE off, the usual legato setup (tables and ADSR still re-init).

Instrument Tables

Each instrument can have a wave, pulse, and filter table. Switch between them with the WAVE / PULSE / FILTER tabs. You edit each table on the instrument that uses it (see Differences from GoatTracker 2). Instruments can still share the same table.

Tables change the sound over time while a note plays. The table is processed row by row, updating wave, pulse, or filter from tick to tick.

With a table row selected, these general table tools are available:

• Delete Row — Removes this table row (and the whole table if it was the last data row).
• Add Row Above — Inserts a copy of this row. Disabled if the table memory is full.
• Add Row Below — Inserts a row below, or creates the table (with a jump row) if it was empty.
• Loop Here — Toggles the table’s jump so it loops to this row (or stops looping).

Selecting a row also shows its controls below.

Wave Table

Controls waveform and pitch over time.

• WAVE — Sets the SID waveform control register with these eight flags. Without Noise, Pulse, Saw, or Triangle, there is no sound.
  • Noise — LFSR noise (pitched hiss).
  • Pulse — Pulse wave. Width comes from the pulse table.
  • Saw — Sawtooth.
  • Triangle — Triangle.
  • Test — Resets the oscillator (silent while on).
  • Ring — Ring-modulates with the previous voice (needs Triangle on this voice).
  • Sync — Hard-syncs this oscillator to the previous voice.
  • Gate — Starts or holds the ADSR envelope. Off begins release.
• DELAY — Hold this step for a number of ticks before moving on. Waveform stays as it was.
• COMMAND — EDIT COMMAND opens the command editor and runs that command from the wave table (same idea as a pattern command). Some commands are not available here.
• RELATIVE — Offset from the current note. Negative goes down.
• ABSOLUTE — Force a fixed pitch.
• NO CHANGE — Leave the pitch unchanged.

Pulse Table

Sets or sweeps the pulse width when the pulse waveform is used.

• SET PULSE WIDTH — Jump to an absolute pulse width.

• MOD PULSE WIDTH — Sweep for STEPS ticks at SPEED (signed). Positive widens, negative narrows. Chain set and mod rows, then Loop Here, for a repeating pulse LFO.

Filter Table

A filter table sets routing, cutoff, and cutoff sweeps. The SID has one filter for all three voices, so cutoff, resonance, and passband apply to every voice routed through it. Routing does not follow the voice this instrument plays on. VOICE 1, VOICE 2, and VOICE 3 are the chip voices: an instrument on voice 3 is filtered only if VOICE 3 is enabled. Bundled presets that use the filter enable VOICE 1 only. Only one filter table runs at a time. A new note on an instrument that has one replaces the filter program already running.

• SET PARAMS — Routes voices through the filter and sets the passband and resonance. The passband buttons can be combined.
  • VOICE 1 / VOICE 2 / VOICE 3 — Sends that voice through the filter.
  • Lowpass — Keeps frequencies below the cutoff.
  • Bandpass — Keeps frequencies around the cutoff.
  • Highpass — Keeps frequencies above the cutoff.
  • RES — Resonance (0–F). Higher gives a sharper peak at the cutoff.

• SET CUTOFF — Jump to an absolute cutoff. Put this directly under SET PARAMS if both should apply on the same tick.

• MOD CUTOFF — Sweep cutoff for STEPS ticks at SPEED (signed), same idea as pulse mod.

Table Sharing Window

Wave, pulse, and filter tables can each be shared between instruments. Editing a shared table changes it for every instrument that uses it.

• Tap another instrument to point this instrument at that instrument’s table (and delete this table if nothing else used it). Instruments that have no table are disabled.
• CLONE — Copies the table to a new unique block. Disabled unless the table is shared and there is room.
• DELETE — Detaches this instrument from the table (and deletes the bytes if this was the last user).
• CLOSE — Closes the window.

Instrument Manager View

Save instruments so you can reuse them across songs, and try the bundled presets to get started quickly. Open with a second tap on INSTR. Load and save always apply to the current instrument.

• FILES — Instruments you have saved.
• PRESETS — Bundled instruments.
• File name (FILES) — Name used when saving.
• LOAD — Loads the selected instrument file or preset into the current instrument.
• SAVE — Saves the current instrument.
• DELETE — Deletes the selected instrument file.

Settings View

Project Settings

• CHIP MODEL — 6581 or 8580.
• SPEED — How often the player ticks. 25Hz is half-speed. 1X is once per PAL frame (50 Hz), 2X twice, and so on. Higher speed means finer timing and denser tables, but also more CPU on a real C64. Changing speed updates the gate timer on empty instruments to 2 × speed (the usual default).
• HARD RESTART — Opens the hard restart window. Shows the current ADSR used for hard restart before a new note.

Hard Restart Window

ADSR written during hard restart (the brief gate-off before a note). It mainly shapes how rapid note passages sound.

• ATTACK / DECAY / SUSTAIN / RELEASE — Default is soft (0F00). Lower values retrigger harder. A little release (for example 0F01) softens the gate-off phase further. Attack F also selects an alternate register write order that can trigger fast releases more reliably.
• CLOSE — Closes the window.

Editor Settings

• FULLSCREEN — Hides the Android status and navigation bars (immersive mode). Swipe from the edge to show them briefly.
• KEEP SCREEN ON — Stops the screen from sleeping while the app is open.
• ROW HEIGHT / HIGHLIGHT — Pattern row size and highlight spacing.
• REG WRITE ORDER — SID register write order v2.68 or v2.73.
• SAMPLING METHOD — Opens the sampling-method window.

Sampling Method Window

• FAST, INTERPOLATE, RESAMPLE INTERPOLATE, RESAMPLE FAST — Picks reSID sampling. The choice applies on tap.
• CLOSE — Closes the window.

Differences from GoatTracker 2

GTMobile songs are still .sng files and play in GoatTracker 2. The file format matches. These are the places the song data is organized differently:

• Tables are per instrument — The song still stores GoatTracker’s packed wave, pulse, filter, and speed tables. GTMobile assigns the pointers. You edit wave, pulse, and filter on the instrument that uses them, not as raw row addresses.
• Speed table — That packed speed table is split into portamento, vibrato, and funk-tempo ranges. Instrument vibrato uses the vibrato range. Pattern commands pick a slot in the matching range, not a raw speed-table address.
• Table pointer commands — In GoatTracker, commands 8, 9, and A store a table address. In GTMobile the data byte is an instrument number (or 00 for off). Playback uses that instrument’s wave, pulse, or filter pointer.
• Shared tables — Several instruments can point at the same table bytes. Sharing, cloning, or dropping that link is how a table is reused or removed. The packed bytes stay hidden.
• Order list — All three voices share one order-list length, and patterns that play on the same row should have the same length. The loop start is a mark on an order row.
• Project settings — Chip model, speed, and hard restart are stored at the end of the song file. GoatTracker ignores that part.