The Covox Speech Thing is an external audio device attached to the computer to output digital sound. It was composed of a primitive 8-bit DAC using a resistor ladder and an analogue signal output, and plugged into the printer port of the PC.
The Speech Thing was introduced on December 18, 1987 by Covox, Inc of Eugene, Oregon, for about US$70 (US$79.95 as of 1989), but as its parts were much cheaper than the complete plug, and as its design was fairly simple, people soon started to build their own variants.
The plug was used long into the 1990s, as sound cards were still very expensive at that time. The plug was also quite popular in the demoscene.
An inherent problem of the design is that it requires very precise resistors. If normal parts are used, the values get shuffled, especially for quiet sounds, resulting in distortion. Nevertheless, the sound quality of the Covox plug is far superior compared to the PC speaker; even today, a self-built Covox plug is still an inexpensive way to give old computers sound capabilities.
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Covox Speech Thing ...
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