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Covox Speech Thing
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<h2 id="features">Features</h2> <p>The Covox plug received an 8-bit digital byte for each digital audio sample from the parallel port and produced a <a href="/facts/High_impedance/DNNoHHvQ">high impedance</a> mono analog output voltage signal though a <a href="/facts/Phone_connector_(audio)/KvpIlV94">mini phone connector</a>. That signal could then be amplified and played back on <a href="/facts/Loudspeaker/tqEjnJ2z">loudspeakers</a>. </p><p>The resistances of the <a href="/facts/Resistor_ladder/mSq5z9lI">R-2R ladder</a> (100 <a href="/facts/K%CE%A9/QNVrlGjw">kΩ</a> and 200 kΩ according to the patent) are deliberately high-enough to prevent excessive <a href="/facts/Electrical_load/IX0XBAqB">loading</a> of the signals, so a printer attached to the output connector will operate normally. </p><p>The original Covox plug itself doesn't use <a href="/facts/Sequential_logic/Rcs4thlu">sequential logic</a> or a <a href="/facts/Clock_signal/9UfTzGHx">clock signal</a>, so theoretically it can operate with any <a href="/facts/Sampling_rate/xxck7aLN">sampling rate</a>. In practice, however, parallel port speed limits make it rather hard to achieve even <a href="/facts/44,100_Hz/7SBI1DYS">standard 44100 Hz</a> (the average 1980s <a href="/facts/Intel_80286/rucEU93g">80286</a> system could handle sampling rates of 12 kHz, while later the faster 33 MHz <a href="/facts/I486SX/8HdtYU7j">486SX</a> introduced in 1991 could handle 44 kHz). </p><p>Its 15 kΩ load resistor in parallel with a 5 <a href="/facts/Nanofarad/gPAYcVoE">nF</a> capacitor after the R2R resistor ladder results in a <a href="/facts/Passivity_(engineering)/7oDeoqd3">passive</a> <a href="/facts/RC_circuit/6WCu8sAc">RC</a> <a href="/facts/Low-pass_filter/QFsUjw7h">low-pass filter</a> starting around 3 <a href="/facts/KHz/6Wshj5qm">kHz</a>, thus limiting the <a href="/facts/Bandwidth_(signal_processing)/7eMDzfJI">analog bandwidth</a>. Many DIY variants do not use the same ladder topology and component values, resulting in different <a href="/facts/Timbre/lVXB949E">timbre</a>.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> </p><p>Another limiting factor was that the CPU had to be <a href="/facts/Interrupt/Mm6C4rpc">interrupted</a> at the sampling rate to play background audio (thus incurring the cost of a <a href="/facts/Context_switch/N0oJQ6CC">context switch</a> for every sample, many thousands of times a second), since there was no <a href="/facts/Data_buffer/tVy4j2Dc">data buffering</a> or <a href="/facts/Direct_memory_access/DWuVgclV">direct memory access</a> available. </p><p>The sound quality can be increased by software through <a href="/facts/Dither/fCBytTzz">dithering</a>, which reduces perceptible <a href="/facts/Aliasing/Pzg84HL0">aliasing</a> noise and increases <a href="/facts/Dynamic_range/zxcuI4Fn">dynamic range</a> (used in Inertia Player and <a href="/facts/FastTracker_2/GsrX6crf">FastTracker 2</a> as an <a href="/facts/Interpolation/8PyetX4f">interpolating</a> option). </p> <h2 id="commercial-products">Commercial products</h2> <ul><li>Covox Speech Thing – a R-2R resistor DAC with parallel port pass through, bundled with speech synthesis software, marketed originally as part of voice synthesis and recognition system.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a></li></ul> <ul><li>Disney Sound Source – a different design to the Covox Speech Thing, though in a superficially similar case also with parallel pass through, marketed by <a href="/facts/Disney_Software/0sXDKm6e">Disney Software</a> in early 1990s. <ul><li>Consists of a <a href="/facts/FIFO_(computing_and_electronics)/RctvBNgE">FIFO buffer</a> with a DAC on the board that plugs into the parallel printer port, which transmits analog audio over a <a href="/facts/Registered_jack/FJIzzlpD">registered jack</a> to a separate amplifier / speaker box.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> Its price was set to only $14<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> 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 Covox Speech Thing which had no <a href="/facts/FIFO_(computing_and_electronics)/RctvBNgE">FIFO buffer</a>, the Disney Sound Source features a 16-byte <a href="/facts/FIFO_(computing_and_electronics)/RctvBNgE">FIFO</a> allowing for autodetection and flow control, which clocks digital output to the resistive DAC at a fixed <a href="/facts/Sample_rate/xxck7aLN">sample rate</a> of 7 kHz ±5%.<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a></li> <li>The printed circuit board DSS007C shows "Ⓟ (1983) U.S. 4,384,170 and others"<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> which is an earlier patent by <a href="/facts/Forrest_S._Mozer/RvsEtX1X">Forrest S. Mozer</a>.<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> The board a has one <a href="/facts/Integrated_circuit/fjn6vg7C">integrated circuit</a> only (labeled "ICS1453") and the schematic<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> shows 8 lines from the parallel port going into one chip with input pins D0-D8 that also has a "DAC output" pin going to an output "sound". So it can be inferred that that single chip implements both the FIFO and DAC internally, which differs dramatically from the passive R-2R design of the original Covox.</li> <li>In 2015 the hardware was reverse engineered so compatible circuits can be built from easily available off the shelf components.<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a> It is also emulated by the popular <a href="/facts/DOSBox/Du2egHYo">DOSBox</a> emulator.</li></ul></li></ul> <h2 id="compatibility">Compatibility</h2> <h3>Games</h3> <p>The Covox plug couldn't directly substitute any of the popular cards of that age (<a href="/facts/AdLib/YWfT5QYY">AdLib</a>, <a href="/facts/Sound_Blaster/tKl0zY5n">Sound Blaster</a>, <a href="/facts/Gravis_UltraSound/WTu5r8lJ">Gravis UltraSound</a>, etc.), but several games / platforms supported it directly. It is also usually used in tandem with an <a href="/facts/AdLib/YWfT5QYY">AdLib</a> sound card as said card officially was a music card and while it could be put into a mode to handle sampled audio, it could not play sampled audio and music at the same time. Notable entries include: </p> <ul><li><i><a href="/facts/688_Attack_Sub/2zbSEym8">688 Attack Sub</a></i> – title music, sound effects</li> <li><i><a href="/facts/Zorro_(1995_video_game)/mMx14ypD">Zorro</a></i> – sound samples</li> <li><i><a href="/facts/Battle_Bugs/NFDKQwaC">Battle Bugs</a></i> – speech, requires <a href="/facts/Expanded_memory/cYurvMxB">expanded memory</a></li> <li><i><a href="/facts/Star_Control_II/qhk8CQWu">Star Control II</a></i> – sounds</li> <li><i><a href="/facts/Pinball_Fantasies/sJdmSdHg">Pinball Fantasies</a></i></li> <li>most older <a href="/facts/Sierra_Entertainment/9B83JIW6">Sierra Entertainment</a> games, such as <i><a href="/facts/King%27s_Quest/V9MzVdw5">King's Quest</a></i> and <i><a href="/facts/Space_Quest/J99ESjFQ">Space Quest</a></i> series</li> <li><a href="/facts/Build_Engine/3dnv60cE">Build Engine</a> games including <i><a href="/facts/Duke_Nukem_3D/Mg07JSKN">Duke Nukem 3D</a></i>, <i><a href="/facts/Redneck_Rampage/jBYpSGEr">Redneck Rampage</a></i> and <i><a href="/facts/Shadow_Warrior_(1997_video_game)/68lUCCDn">Shadow Warrior</a></i></li></ul> <h3>Music trackers</h3> <p>Popular DOS-based <a href="/facts/Music_tracker/anJd8Wul">trackers</a> used in the <a href="/facts/Demoscene/yKunscS7">demoscene</a> included Covox support, for example: </p> <ul><li>Modplay (also <a href="/facts/Modedit/llylN14u">ModEdit</a>, DMP, VP and other Mod players from early 1990s) (Up to 4 channel COVOX output or custom assembler routine for user device)</li> <li>Inertia Player (mono, stereo-on-1 covox, with dithering option).</li> <li>Multiplayer by DGS Italian Software Company</li> <li>Galaxy Music Player (can play MODs even on an <a href="/facts/Intel_8088/DdWKfyBp">Intel 8088</a>)</li> <li><a href="/facts/Scream_Tracker/6wpc0pF6">Scream Tracker</a> version 2.3 direct support. Version 3.21 through virtual-soundblaster driver.</li> <li><a href="/facts/FastTracker/GsrX6crf">FastTracker</a> (mono, stereo, stereo-on-1 mode, with dithering).</li> <li><a href="/facts/Impulse_Tracker/P9kWrw0m">Impulse Tracker</a></li></ul> <h3>Emulating other soundcards</h3> <p><a href="/facts/Emulator/FMHE8qDj">Emulators</a> exist that allow a physical Covox to appear as if it is another soundcard: </p> <ul><li>Virtual SoundBlaster – can emulate Sound Blaster on Covox</li> <li>Covoxer – can emulate <a href="/facts/Tandy_1000/HEIjJKzR">Tandy 1000</a>/<a href="/facts/Tandy_2000/CYoEYHhK">2000</a> music synthesizer</li> <li>TEMU – can emulate <a href="/facts/Tandy_1000/HEIjJKzR">Tandy 1000</a>/<a href="/facts/Tandy_2000/CYoEYHhK">2000</a> music synthesizer and Disney Sound Source</li></ul> <h3>Emulating Covox</h3> <p>The <a href="/facts/DOSBox/Du2egHYo">DOSBox</a> and Fake86 emulators can emulate a virtual Covox (as Disney Sound Source) on machines without a physical Covox.<a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a> </p> <h3>Operating systems</h3> <p>Several operating systems have an installable <a href="/facts/Driver_(software)/0AWbGuMm">driver</a> for Covox: </p> <ul><li><a href="/facts/Windows_3.1x/zYnWyaC6">Windows 3.1x</a>, <a href="/facts/Windows_95/1E1L93qC">Windows 95</a>, <a href="/facts/Windows_98/6qtq4oJm">Windows 98</a></li> <li><a href="/facts/Linux/9FvCKSTq">Linux</a> <ul><li>"Alternate Sound Driver for Linux 2.x" (pcsndrv) – supports a "Mono DAC" using one lp-port (<a href="/facts/Parallel_printer_port/qpkjH8ts">parallel printer port</a>) and a "Stereo DAC" using two lp-ports.<a class="footnote-ref" id="fnref:16" href="#fn:16"><sup>16</sup></a></li> <li>covox-music-player – not a <a href="/facts/Kernel_driver/rDYnHU1G">kernel driver</a>, but rather a <a href="/facts/Userspace/0yIzMY8t">userspace</a> program that outputs sound on modern Linux distros to the Covox via <a href="/facts/Port-mapped_I/O/PmLNFq01">port-mapped I/O</a> with the <i>outb</i> (output byte) <a href="/facts/Opcode/UaLMp56C">instruction</a> <a href="/facts/Wrapper_function/nyy4XUdb">wrapper function</a> (which can be called from user space).<a class="footnote-ref" id="fnref:17" href="#fn:17"><sup>17</sup></a><a class="footnote-ref" id="fnref:18" href="#fn:18"><sup>18</sup></a><a class="footnote-ref" id="fnref:19" href="#fn:19"><sup>19</sup></a></li></ul></li> <li><a href="/facts/MenuetOS/oVIuBCez">MenuetOS</a></li> <li><a href="/facts/CSI-DOS/AM0kqhDb">CSI-DOS</a></li></ul> <h3>Later variants</h3> <ul><li><a href="/facts/Andr%C3%A9_LaMothe/xc3GBHNy">André LaMothe's</a> 1995 book "Black Art of 3D Game Programming" section "Building Your Own Digital Sound Device-DIGIBLASTER"<a class="footnote-ref" id="fnref:20" href="#fn:20"><sup>20</sup></a> – while not saying the word "Covox", it does describe how to build a resistor ladder hardware device with a <a href="/facts/Circuit_diagram/Vqk3udN0">schematic</a> that is essentially a clone of a Covox in stereo that plugs into two parallel printer ports, and describes <a href="/facts/DOS/sWwDXNmX">DOS</a> <a href="/facts/C_(programming_language)/Ky2No763">C code</a> for driving it.</li> <li>Simple LPTsnd<a class="footnote-ref" id="fnref:21" href="#fn:21"><sup>21</sup></a> – also compatible with SoundJR and FTL sound adapters in addition to Covox Speech Thing, allowing more games to be played.</li> <li>CVX-4<a class="footnote-ref" id="fnref:22" href="#fn:22"><sup>22</sup></a> – features <a href="/facts/DIP_switch/chF8LqXM">DIP switches</a> to select capacitor for the low-pass filter, to provide extra attenuation, and to bypass <a href="/facts/Coupling_capacitor/7m9pjCPF">coupling capacitor</a>.</li> <li>Disney Soundsource 2015 Remake<a class="footnote-ref" id="fnref:23" href="#fn:23"><sup>23</sup></a> – <a href="/facts/Reverse-engineered/pmJCV7J7">reverse-engineered</a> from an original adapter. <ul><li>Allows software requiring the original Disney hardware to work without the need of any additional software emulators.<a class="footnote-ref" id="fnref:24" href="#fn:24"><sup>24</sup></a></li></ul></li> <li>Benedikt's remakes: <ul><li>Generic 8 bit audio DAC<a class="footnote-ref" id="fnref:25" href="#fn:25"><sup>25</sup></a> – includes parallel-port pass-through for printer, with intention of being more similar to original Covox.</li> <li>Parallel Port Headphone DAC<a class="footnote-ref" id="fnref:26" href="#fn:26"><sup>26</sup></a> – replica of 1990s SiliconSoft SoundJr device<a class="footnote-ref" id="fnref:27" href="#fn:27"><sup>27</sup></a> that can drive headphones with power from the parallel port.</li> <li>Parallel port audio and joystick adapter<a class="footnote-ref" id="fnref:28" href="#fn:28"><sup>28</sup></a> – compatible with FTL Sound Adapter.</li></ul></li> <li>ISA LPT DAC r0 – Dual-channel board that plugs into the <a href="/facts/ISA_bus/5Rk4bjqB">ISA bus</a>.<a class="footnote-ref" id="fnref:29" href="#fn:29"><sup>29</sup></a> <ul><li>Each channel uses an <a href="/facts/Analog_Devices/xWFzrkre">Analog Devices</a> AD7524<a class="footnote-ref" id="fnref:30" href="#fn:30"><sup>30</sup></a> 8-bit <a href="/facts/Flip-flop_(electronics)/vA99xjM7">latched</a> DAC <a href="/facts/CMOS/NJIWYgBl">CMOS</a> chip containing a precise integrated thin-film resistor network.</li></ul></li></ul> <h2 id="other-covox-products">Other Covox products</h2> <p class="note">Main article: <a href="/facts/Covox/sSWwslff">Covox</a></p> <ul><li>Covox Voice Master – Earlier 1984 speech-synthesis board for the <a href="/facts/Commodore_64/3TPcKDbb">Commodore 64</a> which could playback 64 words stored in memory with <a href="/facts/BASIC/VYMl5TmA">BASIC</a> instructions. Word capacity could be extended with disk or tape.<a class="footnote-ref" id="fnref:31" href="#fn:31"><sup>31</sup></a> <ul><li>Covox Voice Master Junior – Later cheaper ($39.95) variant that plugs into <a href="/facts/Atari/XK95bfqH">Atari</a> joystick port and contains an <a href="/facts/Electret_microphone/j5omEm2H">electret microphone</a> for recording sounds for playback or recognition and a speaker.<a class="footnote-ref" id="fnref:32" href="#fn:32"><sup>32</sup></a><a class="footnote-ref" id="fnref:33" href="#fn:33"><sup>33</sup></a></li></ul></li></ul> <p>Also as described in a 1991 COVOX Company Profile:<a class="footnote-ref" id="fnref:34" href="#fn:34"><sup>34</sup></a> </p> <ul><li>Covox Sound Master – 1984 for <a href="/facts/Apple_II/se82CNvK">Apple II</a>, 1989 for <a href="/facts/MS-DOS/fVrrz1uN">MS-DOS</a></li> <li>Covox Voice Master System II – 1990</li> <li>Covox MIDI Maestro – 1990</li> <li>Covox Sound Master II – 1990</li></ul> <h2 id="external-links">External links</h2> Wikimedia Commons has media related to Covox Speech Thing. <ul><li><a href="https://web.archive.org/web/20191113033645/http://www.epanorama.net/circuits/lptpower.html">Powering devices from PC parallel port</a>, an article on LPT-port devices, including Covox.</li> <li><a href="http://www.mobygames.com/attribute/sheet/attributeId,44/">List of games that support Disney Sound Source</a> at MobyGames.com.</li> <li><a href="http://www.mobygames.com/attribute/sheet/attributeId,43/">List of games that support Covox Speech Thing</a> at MobyGames.com.</li> <li><a href="https://web.archive.org/web/20190722053927/http://margo.student.utwente.nl/el/pc/ad_da/">A collection of software for Covox</a>, including Windows driver.</li> <li>(in Russian) <a href="https://web.archive.org/web/20191113214717/http://www.415.spb.ru/page.php?60">Covox Voice Master schematics and software</a>.</li> <li>(in Russian) <a href="https://web.archive.org/web/20181103030711/http://www.phantom.sannata.ru/konkurs/netskater002.shtml">Covox Digital-Analog Converter</a>, a comprehensive Covox history overview.</li> <li><a href="https://web.archive.org/web/20191111010911/https://www.vogons.org/viewtopic.php?f=62&t=42250">DSS Reverse Engineering on Vogons</a> DSS Reverse Engineering Thread</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>"Speech Thing trademark". United States Patent and Trademark Office (USPTO). <a href="https://tsdr.uspto.gov/#caseNumber=73714260&caseType=SERIAL_NO&searchType=statusSearch" target="_blank">https://tsdr.uspto.gov/#caseNumber=73714260&caseType=SERIAL_NO&searchType=statusSearch</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Stefan, Göhler. "Phonomenal! Covox Speech Thing / Disney Sound Source (1986 / 199x)". Crossfire Designs. Retrieved January 23, 2023. <a href="https://www.crossfire-designs.de/index.php?lang=en&what=articles&name=showarticle.htm&article=soundcards/&page=5" target="_blank">https://www.crossfire-designs.de/index.php?lang=en&what=articles&name=showarticle.htm&article=soundcards/&page=5</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Social Science Microcomputer Review. 7. Duke University Press: 97. 1989. ISSN 0885-0011. {{cite journal}}: Missing or empty |title= (help) <a href="/wiki/ISSN_(identifier)" target="_blank">/wiki/ISSN_(identifier)</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>US4812847A, Stewart, John L. & Stewart, Bradley C., "Parallel port pass-through digital to analog converter", issued 1989-03-14 <a href="https://patents.google.com/patent/US4812847/en" target="_blank">https://patents.google.com/patent/US4812847/en</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Brychkov, Eugeny (October 19, 2012). Adding a multimedia capability: a Covox device (PDF). GR8BIT. Archived from the original (PDF) on February 1, 2014. <a href="https://web.archive.org/web/20140201185718/http://kb.gr8bit.ru/GR8BIT-KB0010-Adding-multimedia-capability-covox-device-23102013.pdf" target="_blank">https://web.archive.org/web/20140201185718/http://kb.gr8bit.ru/GR8BIT-KB0010-Adding-multimedia-capability-covox-device-23102013.pdf</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Scali (November 28, 2017). "The Covox years". Scali's OpenBlog. Archived from the original on February 20, 2023. Retrieved June 25, 2023. <a href="https://scalibq.wordpress.com/2017/11/28/the-covox-years/" target="_blank">https://scalibq.wordpress.com/2017/11/28/the-covox-years/</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>Pilgrim, Aubrey (1996). Build Your Own Multimedia PC. McGraw-Hill. p. 282. ISBN 978-0-07-912226-1. <a href="978-0-07-912226-1" target="_blank">978-0-07-912226-1</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>Phillips, Mark. "Some notes on programming for the Disney Sound Source". Archived from the original on January 1, 2007. <a href="https://web.archive.org/web/20070101124905/http://thorkildsen.no/faqsys/docs/progss.txt" target="_blank">https://web.archive.org/web/20070101124905/http://thorkildsen.no/faqsys/docs/progss.txt</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>"The Oldskool PC Carnival Sideshow". 1999. Retrieved August 6, 2017. <a href="http://www.oldskool.org/shrines/carny" target="_blank">http://www.oldskool.org/shrines/carny</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>"The Sound Source Programmer's Guide" (PDF). Video Game Music Preservation Foundation. Archived (PDF) from the original on June 25, 2023. Retrieved June 25, 2023. <a href="http://www.vgmpf.com/Wiki/images/8/8f/The_Sound_Source_-_Programmer%27s_Guide.pdf" target="_blank">http://www.vgmpf.com/Wiki/images/8/8f/The_Sound_Source_-_Programmer%27s_Guide.pdf</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>"Disney Sound Source Pinout \ VOGONS". www.vogons.org. Archived from the original on May 2, 2023. Retrieved June 26, 2023. <a href="https://www.vogons.org/viewtopic.php?t=48604" target="_blank">https://www.vogons.org/viewtopic.php?t=48604</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>US4384170A, Mozer, Forrest S. & Stauduhar, Richard P., "Method and apparatus for speech synthesizing", issued 1983-05-17 <a href="https://patents.google.com/patent/US4384170/en" target="_blank">https://patents.google.com/patent/US4384170/en</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>Programmer's Guide to the Disney Sound Source. <a href="http://archive.org/details/dss-programmers-guide" target="_blank">http://archive.org/details/dss-programmers-guide</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> <li id="fn:14"><p>"Reversing the Disney Sound Source". VOGONS. February 1, 2015. 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