The Covox Speech Thing is an external audio device that attaches to a computer and provides digital sound output. It connects through a parallel port and produces 8-bit mono sound through a DAC that uses a resistor ladder and an analogue signal output. This is not as efficient as using DMA, so the Speech Thing is processor intensive. Though the Speech Thing is not capable of synthesizing music through FM synthesis, it can play music as digital audio, but long digital tracks take up much more disk space, which was a premium at the time, so few games took advantage of this feature.
The circuit was initially marketed in 1987 by Covox, Inc. of Eugene, Oregon, at a price of around $70. It remained in popular use well into the 1990s until the price of superior sound cards began to drop and overtook the market.
Later sound cards like Sound Blaster could synthesize music as well as play back digital audio, and they used DMA to offset the necessary processing power needed for audio playback.
DOSBox has the ability to emulate a Speech Thing through software.
- en.wikipedia.org/wiki/Covox_Speech_Thing - Wikipedia.