Fall 1995
© IEEE Computer Society Press.

The Amiga MOD Format

From: norlin@mailhost.ecn.uoknor.edu (Norman Lin)

MOD files are music files containing 2 parts:

  1. a bank of digitized samples
  2. sequencing information describing how and when to play the samples

MOD files originated on the Amiga, but because of their flexibilityand the extremely large number of MOD files available, MOD playersare now available for a variety of machines (IBM PC, Mac, SparcStation, etc.)

The samples in a MOD file are raw, 8 bit, signed, headerless, lineardigital data. There may be up to 31 distinct samples in a MOD file,each with a length of up to 128K (though most are much smaller; say,10K - 60K).
An older MOD format only allowed for up to 15 samples ina MOD file; you don't see many of these anymore.
There is no standardsampling rate for these samples. [But see below.]

The sequencing information in a MOD file contains 4 tracks of information describing which, when, for how long, and at what frequency samples should be played. This means that a MOD file can have upto 31 distinct (digitized) instrument sounds, with up to 4 playingsimultaneously at any given point. This allows a wide variety of orchestrational possibilities, including use of voice samplesor creation of one's own instruments (with appropriate sampling hardware/software). The ability to use one's own samples as instruments is a flexibility that other music files/formats do not share, andis one of the reasons MOD files are so popular, numerous, and diverse.

15 instrument MODs, as noted above, are somewhat older than 31instrument MODs and are not (at least not by me) seen very oftenanymore. Their format is identical to that of 31 instrument MODsexcept:

  1. Since there are only 15 samples, the information for the last (15th) sample starts at byte 440 and goes through byte 469.
  2. The song length is at byte 470 (contrast with byte 950 in 31 instrument MOD)
  3. Byte 471 appears to be ignored, but has been observed to be 127. (Sorry, this is from observation only)
  4. Byte 472 begins the pattern sequence table (contrast with byte 952 in a 31 instrument MOD)
  5. Patterns start at byte 600 (contrast with byte 1084 in 31 instrument MOD)

"ProTracker," an Amiga MOD file creator/editor, is available for ftp everywhere as pt??.lzh.

From: Apollo Wong (apollo@ee.ualberta.ca)

From: M.J.H.Cox@bradford.ac.uk (Mark Cox)
Newsgroups: alt.sb.programmer
Subject: Re: Format for MOD files...
Message-ID: <1992Mar18.103608.4061@bradford.ac.uk>
Date: 18 Mar 92 10:36:08 GMT
Organization: University of Bradford, UK

wdc50@DUTS.ccc.amdahl.com (Winthrop D Chan) writes:
> I'd like to know if anyone has a reference document on the format of the
> Amiga Sound/NoiseTracker (MOD) files. The author of Modplay said he was going
> to release such a document sometime last year, but he never did. If anyone

I found this one, which covers it better than I can explain it - if you use this in conjunction with the documentation that comes with NormanLin's Modedit program it should pretty much cover it.

Mark J Cox

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