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The Covox Speech Thing (also known as Covox plug) was an external audio device attached to the computer to output digital sound. It was composed of the most primitive 8-bit DAC using a resistor ladder and an analogue signal output, and plugged into the printer port of the PC. The circuit was marketed around 1986 by Covox, Inc of Eugene, Oregon, for about 70 USD (79.95 USD 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. == Commercial products == * Covox Speech Thing. The simplest hardware DAC, bundled with speech synthesis software, marketed originally as part of voice synthesis and recognition system. * Disney Sound Source. Covox-idea based DAC, marketed by Disney Software in early 1990s. It consisted of 2 parts: a DAC plugged into printer port and separate amplifier / speaker box. Its price was set to only $14〔(The Oldskool PC Carnival Sideshow )〕 and it was supported by many games (see below). It used external power (9 volt battery) and could be turned on/off by software. Contrary to the Speech Thing the output rate is determined by the hardware (7 kHz) and the design features a 16 byte FIFO allowing for autodetection and flow control of the output. In 2015 the hardware was reversed so compatible circuits can be build from easily available off the shelf components.〔()〕 It is also emulated by the popular DOSBox emulator. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Covox Speech Thing」の詳細全文を読む スポンサード リンク
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