furnace/doc/1-intro/glossary.md

# glossary of common terms

**2-op**, **3-op**, **4-op**...: the number of FM operators used to generate a sound. more operators allow for more complex sounds.

**ADPCM**: adaptive differential pulse code modulation. this is a variety of DPCM with a more complex method of storing the amplitude differences.

**ADSR**: attack, decay, sustain, release. these are the four necessary values for a basic volume envelope.

**algorithm**: the way in which the operators in an FM instrument interact.
- when two operators connect to the same point, their sounds are added together.
- when two operators are connected left to right, the left is the modulator and the right is the carrier sound that is modified.

**bitbang**: to achieve PCM sound by sending a rapid stream of volume commands to a non-PCM channel.

**BRR**: a lossy sample format used by the SNES. it has a fixed compression ratio; groups of 32 bytes (16 samples) are encoded in 9 bytes each.
- usually stored in .brr files.

**clipping**: when a sample or playback stream exceeds the maximum or minimum values. this can cause audible distortion.
- this often occurs when a sample is amplified too much.
- it can also occur during playback if too much sound is being added together at once. in some cases the mixer can be used to reduce the volume. if this doesn't work, the clipping is caused within the chip's own mixing, and the only solution is to reduce the volumes of the notes being played.

**clock rate**: the timing at which a chip operates, expressed as cycles per second (Hz).
- changing this may change aspects of how some chips work, most notably pitch.
- some chips cannot operate at anything other than their designed clock rate.

**cursor**: the marker of input focus. anything typed will happen at the cursor's location.
- _Furnace:_ this always refers to the pattern view except when in a text entry box.

**DAC**: digital analog converter. this converts a digital representation of sound into actual output.

**.dmf**: a DefleMask song file.
- _Furnace:_ DFM files may be read, and compatibility flags will be set to make them play as accurately as possible, but there may still be glitches.
- _Furnace:_ DFM files may be saved, but full compatibility isn't guaranteed and many features will be missing. this isn't recommended unless absolutely necessary.

**.dmp**: a DefleMask instrument file.

**.dmw**: a DefleMask wavetable file.

**DPCM**: differential/delta pulse code modulation. this is a variety of PCM that stores each amplitude as its difference from the previous.

**duty**: in a pulse wave, this represents the ratio of the "on" part of the wave.
- a square wave is a pulse wave with a duty of 50%.

**feedback**: in FM instruments, this adds some of an operator's output into itself to create complex harmonics.
- in the algorithm view, an operator with a circle around it is capable of feedback.

**FM**: frequency modulation. this is a method of generating sound that uses one operator's amplitude to modify another operator's frequency.
- the FM in Yamaha chips is more accurately called _phase modulation,_ which uses a different method of computation to achieve similar results.

**.fui**: a Furnace instrument file.

**.fur**: a Furnace tracker file.

**.fuw**: a Furnace wavetable file.

**hard-pan**: sounds can only be panned all the way to one side or the other, not in-between.

**Hz**: hertz (pronounced as "hurts"). a unit representing divisions of one second. 1 Hz means once per second; 100 Hz means one hundred times per second. also, _kHz_ (kilohertz, one thousand per second) and _MHz_ (megahertz, one million per second).

**interpolate** (pattern): to fill in the area between two values with a smooth ramp of values in between.

**interpolation** (sample): filtering of sample output to remove unintended harmonics and achieve a smoother sound.
- analogous to image antialiasing.
- some sample-based chips can perform interpolation, but most cannot.

**ladder effect**: an inaccurate yet common term for the DAC distortion that affects some Yamaha FM chips.

**LFO**: low frequency oscillator. this is a slow, often subsonic oscillator used to alter other sounds.

**macro**: a sequence of values automatically applied while a note plays.

**noise bass**: the technique of using a PSG's periodic noise generator with a very short period to create low-frequency sounds.

**normalize**: to adjust the volume of a sample so it is as loud as possible without adding distortion from clipping.

**operator**: in FM, a single oscillator that interacts with other oscillators to generate sound.

**oscillator**: a sine wave or other basic waveform used as sound or to alter sound.

**PCM**: pulse code modulation. a stream of data that represents sound as a rapid sequence of amplitudes.
- CD tracks and .wav files are PCM.
- .flac files are compressed PCM that must be converted to .wav outside Furnace before use.
- .ogg and .mp3 are compressed differently from PCM. they must also be converted to .wav before use.

**period**: the length of a repeating waveform. as frequency rises, the period shortens.

**periodic noise**: an approximation of random noise generated algorithmically.
- the period is the number of values generated until the algorithm repeats itself.

**phase reset**: to restart a waveform at its initial value.
- for FM instruments, this restarts the volume envelope also.

**PSG**: programmable sound generator. this refers to chips that produce only simple waveforms and noise.

**pulse wave**: a waveform with a period consisting of only two amplitudes, high and low. also known as a rectangular wave.
- the ratio of the durations of the high and low parts is known as the duty of the wave.
- a square wave is a pulse wave for which the ratio of high and low are exactly equal, having a duty of 50%.

**release**: the part of a note that plays after it's no longer held, or the part of a macro the plays after it stops looping. usually applies at key off.

**resample**: to convert a sample to a different playback rate.
- this is a "lossy" process; it usually loses some amount of audio quality. the results can't be converted back into the original rate without further loss of quality.
- resampling to a lower rate reduces the amount of memory required, but strips away higher frequencies in the sound.
- resampling to a higher rate cannot recover missing frequencies and may add unwanted harmonics along with greater memory requirements.

**raw**: a sample or wavetable file without a header. when loading such a file, the format must be set properly or it will be a mess.

**register**: a memory location within a sound chip. "register view" shows all the relevant memory of all chips in use.

**sample** (1): a digitally recorded sound. usually stored as some variant of PCM.
- these can take up a lot of room depending on length and sample rate, thus older systems tend to use short, lower quality samples.

**sample** (2): a single value taken from a digitally recorded sound. a sample(1) is made up of samples(2).

**signed**: a digital representation of a number that may be negative or positive.
- if an imported raw sample sounds recognizable but heavily distorted, it's likely to be unsigned interpreted as signed or vice-versa.

**software mixing**: mixing multiple channels of sound down to a single stream to be sent to a PCM channel.
- this puts a heavy load on the CPU of the host system, so it was rarely used in games.
- _Furnace:_ this is used for DualPCM and QuadTone.

**square wave**: a wave consisting of only two values, high and low, with equal durations within the wave's period.
- this is equivalent to a pulse wave with a duty of 50%.

**supersaw**: a sound made up of multiple saw waves at slightly different frequencies to achieve a chorusing effect.

**tick rate**: the rate at which the software controlling a sound chip sends commands to it.
- this usually corresponds to the frame rate the system uses for video, approximately 60 for NTSC and 50 for PAL.

**unsigned**: a digital representation of a number that can only be positive.
- if an imported raw sample sounds recognizable but heavily distorted, it's likely to be signed interpreted as unsigned or vice-versa.

**.vgm**: a file containing the log of data sent to a soundchip during sound playback.
- saving to a .vgm file may be compared to "converting text to outlines" or similar irreversible processes. the results cannot be loaded back into the tracker.
- different versions of the VGM format have different capabilities, with trade-offs. older versions may lack chips or features; newer versions may not be compatible with some software.
- samples are stored uncompressed. PCM streams (such as DualPCM) can quickly take up a huge amount of space.

**waveform**: a very short period of repeating sound.
- the most basic waveform is a sine wave. others include triangle, pulse, saw, and the like.

**wavetable** (1): a very short looping sample.

**wavetable** (2): an ordered group of wavetables(1) used in sequence within a single instrument.

**.zsm**: a VGM-like file meant specifically for the Commander X16 computer.