Covox variants

Several inexpensive Covox variants appeared in the late 1980s as a cheap way to get digital audio output from a PC. These small digital-to-analog converter (DAC) devices were far simpler than a Sound Blaster — just a dongle that plugged into the parallel port, also known as the LPT (Line Print Terminal) port — but they could play back digitized sound and speech at decent quality for the era. For this reason, they are also sometimes called LPT DAC devices.

Covox Speech Thing

Released in 1986, the Covox Speech Thing (or just Covox) was a simple, cheap DAC that plugged into the parallel port - popular enough that it was often built as a DIY project. It provided 8-bit mono audio output and was supported by around 60 games, including several Sierra titles.

Disney Sound Source

Introduced in 1990, the Disney Sound Source was a parallel port audio device backwards-compatible with the Covox Speech Thing, but with lower CPU overhead during playback. It was supported by around 150 games, making it the most popular parallel port audio device. dosbox-automation emulates the Disney Sound Source, which is also compatible with Covox Speech Thing titles and Intersound MDO software.

Stereo-on-1 DAC

The Stereo-on-1 was a stereo variant of the parallel port DAC concept, splitting the signal into left and right channels at the cost of halving the bit depth. Less common than the mono Covox, but supported by some tracker music players and a handful of games.

Mixer channels

The Covox Speech Thing outputs to the COVOX mixer channel, the Disney Sound Source to the DISNEY channel, and the Stereo-on-1 to the STON1 channel.

Configuration settings

Parallel port DAC settings are to be configured in the [speaker] section.

lpt_dac

Type of DAC plugged into the parallel port.

Possible values:

lpt_dac_filter

Filter for the LPT DAC audio device(s).

Possible values:

• on (default) -- Filter the output. The default filter varies by device:

  Device	Default filter	Equivalent setting
  Disney Sound Source	2nd order high-pass at 100 Hz, and 2nd order low-pass at 2 kHz	hpf 2 100 lpf 2 2000
  Covox Speech Thing	2nd order low-pass at 9 kHz	lpf 2 9000
  Stereo-on-1	2nd order low-pass at 9 kHz	lpf 2 9000

• off -- Don't filter the output.

• <custom> -- Custom filter definition; see Custom filter settings for details.