.MOD File Format

Introduction

A multichannel module is a tracker module with 31 samples and any number of channels from 1 to 32 other than 4. The Amiga plays four sounds at once, but trackers on the PC, which mix the sound in software, could play more, and wrote modules in the Amiga layout with wider patterns: one 4-byte cell for every channel in each row. The signature at offset 1080 gives the count, as in 6CHN, 8CHN, 16CH or 32CH.

The tags with a digit and CHN are usually credited to FastTracker 1 (Triton, 1993), which had 8 channels; FastTracker 2 and other PC trackers wrote the two-digit xxCH tags for up to 32 channels. TakeTracker, and Octalyser on the Atari STe and Falcon, had signatures of their own. OpenMPT and most players on today’s computers still read them.

The header is the same as a 4-channel module’s, but because the size of every pattern changes with the count, a reader that assumes 4 channels reads all of them wrongly: this is a separate format. All counts share it, because the rule is the same, the size from the signature. A 4-channel module with a signature such as 4CHN is laid out exactly like an M.K. one and is read as a ProTracker module.

A .mod file dropped on any page of this site opens in the explorer, which shows the header field by field, the samples, the order list and every pattern note by note, and plays the song with ProTracker’s replay routine, extended to the channel count.

Structure

A 1,084-byte header, then the patterns, then the sample data, with nothing between them. All numbers are big-endian. With C channels, a row is 4 × C bytes and a pattern 256 × C bytes.

Telling it apart

The explorer’s parser for this format checks two things: the file is at least 1,084 bytes long, and the four bytes at offset 1080 are one of these signatures, for a count from 1 to 32 other than 4. The count then sets the row size.

A signature with a count of 4 (4CHN, 04CH, TDZ4) belongs to the ProTracker module, and FLT8 and EXO8, which also mean 8 channels, to the StarTrekker module, whose patterns are stored differently. A file with any other bytes at 1080 is turned down, and the explorer tries the parsers for the other module formats. Everything after the signature is read as it comes, and problems are reported rather than grounds for turning the file down.

Variants

• ProTracker module (M.K.) – 31 samples and 4 channels, marked M.K. at offset 1080: the standard Amiga module
• Multichannel module (xCHN, xxCH) – 31 samples and 1 to 32 channels, marked 6CHN, 8CHN, 16CH and so on
• StarTrekker 8-channel module (FLT8) – 8 channels, each pattern stored as two 4-channel patterns
• Soundtracker module (15 samples) – the first modules, 1987 to 1989: 15 samples and no signature

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