.VOC File Format

Introduction

VOC is the sound file of Creative Labs’ Sound Blaster cards, from the MS-DOS era. Many DOS games stored their speech and sound effects as VOC files, and the tools that came with the card recorded and played them. The audio is usually 8-bit unsigned PCM, and the file can also hold silence, markers, text and repeat loops.

Structure

The file starts with the text Creative Voice File and the byte 1A, 20 bytes in all. Three little-endian 16-bit values follow: the offset of the first block (usually 26), the version (such as 0x010A or 0x0114) and a check value equal to the complement of the version plus 0x1234.

The rest is a list of blocks. Each block starts with a type byte and a 24-bit length. Type 1 holds sound data, starting with a time constant byte (the sample rate is 1000000 / (256 − time constant)) and a codec byte. Type 2 continues the previous sound data. Other types give silence (3), a marker (4), text (5), the start and end of a repeat (6 and 7), extended settings for stereo and high rates (8), and sound data with an explicit sample rate, bit depth and channel count (9). A block of type 0 ends the file.

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