Sound lumps in the WAD file are stored in raw (PCM) format for 8-bit, monaural, typically at a sampling rate of 11025 Hz, although some sounds use 22050 Hz. 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.