Sound

The sounds in Doom and Doom 2 were compiled by Bobby Prince, and many of them are from various royalty-free sound libraries. The sound support for Doom was programmed by Paul Radek.

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.

Doom also provides for PC speaker sounds, which consist of various blips and bleeps 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