Sound

The sounds in Doom and Doom II were compiled by Bobby Prince, and in Heretic and Hexen compiled by Kevin Schilder. Many of them are from various royalty-free sound libraries.

The sound support for the Doom engine was programmed by Paul Radek. Because of legal issues regarding his sound library, the original DOS source code could not be distributed freely.

Sound lumps in the WAD file are stored in raw (PCM) format for 8-bit, monaural, 11025 Hz sampling rate audio. Each sample is one byte (8 bits), and in vanilla Doom, the maximum number of samples was 65535. At a sampling rate of 11025 Hz, this meant the longest sound could be about six seconds.

The Doom engine also provides for PC speaker sound effects, which consist of various tones played through the PC speaker. Other than playing without sound, this was the only option for those who did not own a sound card when the game was released.

Source

 * Unofficial Doom Specs