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MOD (file format)

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MOD
File extension:	`.mod`
Developed by:	Karsten "Obi" Obarski
Type of format:	Music

MOD is a computer file format used primarily to represent music, and was the first module file format. MOD files use the “.MOD” file extension, except on the Amiga where the original trackers instead use a “mod.” prefix scheme, e.g. “mod.echoing”. A MOD file contains a set of instruments in the form of samples, a number of patterns indicating how and when the samples are to be played, and a list of what patterns to play in what order.

1 History
2 Format overview
3 Time
4 Other MOD formats
5 See also
6 External links

History

The first version of the format was created by Karsten Obarski for use in the Ultimate Soundtracker; tracker software released for the Amiga computer in 1987 [1]. The format has since been supported by hundreds of playback programs and dozens of other trackers. The original version of the MOD format featured four channels of simultaneous audio playback, corresponding to the capabilities of the original Amiga chipset, and up to 15 instruments. Later variations of the format have extended this to up to 32 channels and 31 instruments. The format was designed to be directly playable on the Amiga without additional processing: for example, samples are stored in 8-bit PCM format ready to be played on the Amiga DAC, and pattern data is not packed. Playback required very little CPU time on an Amiga, and many games used MOD files for their background music. A common misconception is that the magic number "M.K." in the 0x438 offset of MOD files are the initials of Mahoney and Kaktus, two prominent Amiga demosceners at the time, who played an important part in the popularity of the format. They in fact stand for the initials of Michael Kleps a.k.a. Unknown / DOC, another important developer of the format. [2] [3]

Format overview

A pattern is typically represented in a sequencer user interface as a table with one column per channel, thus having 4 columns; one for each Amiga hardware channel. Each column has 64 rows. A cell in the table can cause something to happen on its column's channel when its row's time is reached:

Start an instrument playing a new note in this channel at a given volume, possibly with a special effect applied on it
Change the volume or special effect being applied to the current note
Change pattern flow; jump to a specific song or pattern position or loop inside a pattern
Do nothing; any existing note playing in this channel will continue to play

An instrument is a single sample along with an optional indication of which portion of the sample can be repeated to hold a sustained note.

Time

In the original MOD file the minimum time frame is 0.02 seconds, or a vertical blanking, because the original software used the VSync of the monitor running at 50 Hz (for PAL) or 60 Hz (for NTSC) for timing. The rate at which pattern data is played is defined by a speed setting. Each row in pattern data lasts one vertical blanking (or 0.02 seconds) times the current speed setting. The speed setting varied from 1 to 255. In later versions of the format, the vertical blanking was replaced with an adjustable time period staying in range [0.01, 0.078] seconds. The old speed setting command was replaced with a new one that was used to change both the old speed setting and the new adjustable time period. Unfortunately, some of the old functionality was broken, because the new speed setting command had identical code value to the old one. Values in range [1,31] were interpreted as old speed settings, but other values were regarded as modifications to the adjustable time period. Hence, values in range [32, 255] used in some old songs broke in new versions of the player. For more info about the MOD format see the alt.binaries.sounds.mods FAQ.

Other MOD formats

MOD is also the file extension for several other applications:

It is the video file format used on many digital camcorders, such as the JVC Everio, and the Panasonic D-Snap SD-card camcorders. Typically, such files are actually MPEG-2 video files with a different extension. To play such .mod files, it is not necessary to convert them but in most cases simply rename their extension to .mpg.
It is used for game modules by the game Neverwinter Nights.
It is used for AMPL module files
It is used for the old phpBB Modification Templates