Glossary

This page contains some terminology used throughout the manual.

Hardware

APU

The APU, or audio processing unit, is the hardware component that handles sound output.

Channel

A channel is a part of the APU that generates a waveform. The Game Boy has 4 channels for use, two pulse channels, one waveform channel and one noise channel. Channels are often abbrievated as CHx where x is the channel number from 1-4.

Pulse channel

The pulse channel is a channel that generates a rectangular waveform. Channels 1 and 2 are pulse channels. Each pulse channel has 4 different duty settings. See the pulse channel page for more details.

Wave channel

The wave channel is a channel that generates a waveform from a customizable 32-step waveform or wavetable. Channel 3 is a wave channel. See the wave channel page for more details.

Noise channel

The noise channel is a channel that generates white noise via a linear feedback shift register (LFSR). Channel 4 is a noise channel. See the noise channel page for more details.

Envelope

The envelope is a hardware volume envelope that handles linear volume sweeps. Only channels 1, 2 and 4 have an envelope. These channels are also referred to as envelope channels. See the envelope page for more details.

Sweep

The sweep is a hardware frequency sweep for channel 1. When activated the sweep modifies the channel's frequency by increasing or decreasing it periodically. See the sweep page for more details.

DAC

A DAC is a digital to analog converter. Each channel has a DAC which converts the digital signal created by the channel to an analog one which is mixed and outputted to the speakers.

Mixer

The mixer combines all signals from each channel's DAC and sends it to the speakers. The mixer contains a global volume setting for each terminal, as well as switches for channel DAC output to each terminal.

Terminal

Output to be sent to a speaker. The Game Boy has stereo sound so there are two terminals, one for the left speaker and one for the right speaker. If headphones are not used, both terminals are combined into a mono output and is sent to the Game Boy's builtin speaker.

Register

Register refers to the memory mapped hardware registers of the APU. The APU is controlled by writing to these registers. Registers are referenced by the following naming scheme: NRxy where x is the channel (or 5 for the control registers) and y is the register number.

Playback

Driver

A sound driver handles music and sound effect playback on a Game Boy by periodically updating its APU registers.

Engine

The engine is responsible for playing music and in the future, sound effects. The engine behaves similarly to a driver, but differs in that it runs on your PC and sends register writes to an APU emulator.

Halt

A halt is an operation that ends playback of a song. Halts can be performed by the song via the C00 effect, or forcibly by the application.

Locked/Unlocked

A channel is locked if it has music playing on it, otherwise it is unlocked and can be used for other purposes (typically sound effects). See the Channel lock mechanism page for more details.

Music Runtime

Used internally by the tracker's engine to manage the playback of a song. The runtime only plays one song indefinitely or until it halts. A new runtime is constructed for each song that is played or restarted.

Speed

Tracker playback speed in units of frames/row, in fixed point format Q4.4. See the Speed page for more details.

Data

Pattern

A pattern is a collective of 4 tracks, one for each channel.

Order

An order is the layout of a song, as a list of order rows. Each row in the order specifies a pattern, which the song will play from first to last. When the last order has finished playing, the song loops back to first one.

Order Row

A row in the order. An order row contains four track ids, one for each channel.

Row

A row is a singular piece of music data. A track row is a single row in a Track, whereas a pattern row is a single row in a pattern, or a collective of 4 track rows.

Column

A cell or part of a track row. There are three types of columns:

1. Note
2. Instrument
3. Effect

Note

A note is a specific frequency setting. A note is also a type of column that indicates the row will start a note. A channel can only be started by using a note column.

There are two types of notes: tone and noise. A tone note represents a frequency that is playable on the pulse and wave channels. Tone notes range from C-2 to B-8. Concert pitch is used with some notes being off key due to hardware limitations. A noise note represents a frequency setting that is only playable on the noise channel. Noise notes range from C-2 to B-6, and each note is used as an index in a lookup table that results in a unique frequency setting for the noise channel. Noise frequencies are sorted from the lowest at C-2 to the highest at B-6.

For more details on these notes see the Octave Range page.

Instrument

An instrument is a tool for manipulating the feel, volume and overall sound of a channel when a note is played. An instrument accomplishes this by modifying the state of channel using sequences. See the Instrument page for more details on their operation.

Waveform

A waveform is a 16-byte sequence of nibbles that is used for the wave channel's wavetable. The upper nibble of the first byte is the first sample in the wavetable

Sequence

A sequence is an array of bytes that are used by instruments to manipulate a channel's parameter. They are similar in function to what other trackers call macros. Sequences can also have a loop index, which will cause the instrument to loop back to that index when the end of the sequence is reached.