Most sound

Daniel Vik
802 Durshire Way
Sunnyvale, Ca 94087
daniel@vik.cc
http://www.danielvik.com

Judges' comments:

To build:

make vik

To run:

./vik file.mod > audio_file.raw

Try:

./vik randowan.mod | mplayer -demuxer rawaudio -
./vik mad_world.mod | mplayer -demuxer rawaudio -

Alternatively, you can use

./vik file.mod > file.raw; ./raw2wav file.raw > file.wav

It is possible to download a number of Mod files from The Mod Archive.

The randowan.mod and mad_world.mod files were created by Henrik Bertilsson and are included with his permission.

Selected Judges Remarks:

This entry converts .MOD audio files to a playable stream in a most pleasing manner if you don’t like tremolo or vibrato.

Also it abuses the C compiler and/or assembler with a partially initialized 32 MByte array. Can you tell what is that partial initilzation for?

Does it take your system a long time to compile? You may want to do try:

 cc -S vik.c

and to examine the resulting assembly file vik.s. On some platforms the assembly file is about 128 MBytes in size!

Author’s comments:

Introduction

In 1987, Karsten Obarski changed the way music was handled in games and demos with the introducton of the MOD file format on Commodore Amiga.

A MOD file contains a set of samples, a number of patterns indicating how and when the samples are to be played, a list of what patterns to play in what order, and a number of effects.

Features

This program converts MOD files created with the standard trackers for Amiga, e.g. Pro Tracker, Noise Tracker and Sound Tracker to raw 16 bit 44.1kHz stereo audio. The program supports MOD music with 4, 6, and 8 channels MOD files with up to 31 samples.

The MOD format includes many effects for each audio channel and this program supports most of them, including:

Arpeggio
Slide and fine slide up/down/to note
Set sample offset
Volume slide
Pattern break
Filter on/off
Set volume
Cut sample
Delay sample
Delay pattern
Set speed

Due to size constraints tremolo and vibrato is not supported. Also, to avoid infinite long songs, the position jump feature is ignored.

Songs

With his permission, the package incldues two songs composed by Henrik Bertilsson, also known as Deelite:

Mad World
Randowan

Build

Compiling for *nix systems (including cygwin) is straight forward:

$ gcc -o vik vik.c

Usage

Convert MOD file to raw 44.1kHz stereo audio file

$ ./vik mad_world.mod > audio_file.raw

Listen to the MOD file (streaming to mplayer)

$ ./vik randowan.mod | mplayer -demuxer rawaudio -

(Don’t forget the last ‘-’ as it makes mplayer read from stdin.)

Obfuscation

The IOCCC rules did not put a limit on the entropy of the source code, and it appears that the general entropy rules doesn’t apply. An estimate is that the code density entropy of this entry is ~1.2 which means that there are around 2500 characters of code carrying information, yet there are only 2037 IOCCC characters of actual code. Most of the additional characters are encoded with non-counting characters in the frequency table. But there are also ~50 or so white space characters spread out through the source code that carry information.

The use of macros certainly adds to the obfuscation but the reason for using them is mainly to fit as many features as possible within the size limits. So please excuse the use of them.

Once the preprocessor is run, the code gets more interesting. The MOD player is basically a register based state machine and all the magic is hidden in a fog of short statements. Many of the register updates are conditional and the program uses the ? operator (sigh) mainly to save space, but also to leverage the comma operator and precedence more efficiently.

Portability

The progam is portable to most platforms. The only system dependency is that the program relies on writing binary data to stdout.

Microsoft compilers adds a carriges return to newlines, and to compile the program with this platform, the following line can be added after the main declaration in order for the program to run correctly:

_setmode(_fileno(stdout), 0x8000);

Limitations

The program only runs when a valid MOD file is passed as argument. If no argument is passed, the program crashes.