Global InformationCovox Speech Thing information
 Covox Speech Thing | |
| Date invented | October 2, 1987 |
|---|---|
| Invented by | Covox, Inc. |
| Connects to | Parallel printer port |
| Use | audio digital-to-analog converter attached to computer parallel port with pass-through |
| Common manufacturers | Covox, Inc. (original Covox Speech Thing) Disney (Disney Sound Source variant) Faster Than Light (FTL Sound Adapter variant) SiliconSoft (SoundJr variant) Do it yourself variants |
| Introduced | December 18, 1987 |
The Covox Speech Thing is an external digital-to-analog converter (DAC) that plugs into the parallel printer port of a PC. It converts 8-bit digital sound using a simple R-2R resistor ladder into an analog signal output.
The Speech Thing was introduced on December 18, 1987[1] by Covox, Inc. of Eugene, Oregon, for about US$70[2] (equivalent to $188 in 2023) and priced US$79.95 as of 1989.[3] People soon started to build their own (DIY) variants, since its communication protocol and DAC is simple and only requires soldering a few cheap parts. The novelty of its patent "Parallel port pass-through digital to analog converter" (filed in 1987, granted in 1989)[4] wasn't specifically the use of a resistor ladder as a DAC, but rather the patent's discussion is around its ease of plugging into the parallel port and how its resistor ladder design didn't block other devices from using the parallel port. The plug was used long into the 1990s[clarify], 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 its quality relies on how precisely matched the resistors are (see Resistor ladder § Accuracy of R–2R resistor ladders). If unmatched resistors are used, the resulting voltage levels 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 variant is still an inexpensive way to give old computers sound capabilities.[5]
- ^ "Speech Thing trademark". United States Patent and Trademark Office (USPTO).
- ^ Stefan, Göhler. "Phonomenal! Covox Speech Thing / Disney Sound Source (1986 / 199x)". Crossfire Designs. Retrieved January 23, 2023.
- ^ Social Science Microcomputer Review. 7. Duke University Press: 97. 1989. ISSN 0885-0011.
{{cite journal}}: Missing or empty|title=(help) - ^ US4812847A, Stewart, John L. & Stewart, Bradley C., "Parallel port pass-through digital to analog converter", issued 1989-03-14
- ^ Brychkov, Eugeny (October 19, 2012). Adding a multimedia capability: a Covox device (PDF). GR8BIT. Archived from the original (PDF) on February 1, 2014.