Covox Speech Thing
Encyclopedia
The Covox Speech Thing 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 in to 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 orders of magnitude 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 card
s 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.
s. Sampling rate
was not fixed by hardware means, and theoretically Covox can support any sampling rate. In practice, however, LPT port speed limits make it rather hard to achieve even standard CD-quality 44100 Hz. Another limiting factor compared to real sound cards was the need to use the computationally demanding timer interrupt to play background music, since there was no direct memory access
available.
Advanced versions of Covox-like devices featured:
, Sound Blaster
, Gravis Ultrasound
, etc), but several games / platforms supported it directly. Notable entries include:
Popular DOS-based trackers used on demoscene included Covox support, for example:
Also, numerous emulator
s existed, for example, Virtual SoundBlaster could be used to emulate Sound Blaster on Covox, Covoxer could emulate Tandy 1000
/2000
music synthesizer on Covox.
Several operating systems have a driver for Covox available for install:
In reverse, DOSBox
allows to emulate presence of Covox (as Disney Sound Source) on a machine without such physical device connected.
Bit
A bit is the basic unit of information in computing and telecommunications; it is the amount of information stored by a digital device or other physical system that exists in one of two possible distinct states...
DAC
Digital-to-analog converter
In electronics, a digital-to-analog converter is a device that converts a digital code to an analog signal . An analog-to-digital converter performs the reverse operation...
using a resistor ladder
Resistor Ladder
A resistor ladder is an electrical circuit made of repeating units of resistors. Two configurations are discussed below, a string resistor ladder and a R-2R ladder....
and an analogue signal output, and plugged in to the printer port
LPT
LPT is the original, and still common, name of the parallel port interface on IBM PC-compatible computers. It was designed to operate a text printer that used IBM's 8-bit extended ASCII character set. The name derives from the fact that "line printer" was a common generic term at the time for any...
of the PC
IBM PC compatible
IBM PC compatible computers are those generally similar to the original IBM PC, XT, and AT. Such computers used to be referred to as PC clones, or IBM clones since they almost exactly duplicated all the significant features of the PC architecture, facilitated by various manufacturers' ability to...
.
The circuit was marketed around 1986 by Covox, Inc of Eugene, Oregon
Eugene, Oregon
Eugene is the second largest city in the U.S. state of Oregon and the seat of Lane County. It is located at the south end of the Willamette Valley, at the confluence of the McKenzie and Willamette rivers, about east of the Oregon Coast.As of the 2010 U.S...
, for about 70 USD (79.95 USD as of 1989), but as its parts were orders of magnitude 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 card
Sound card
A sound card is an internal computer expansion card that facilitates the input and output of audio signals to and from a computer under control of computer programs. The term sound card is also applied to external audio interfaces that use software to generate sound, as opposed to using hardware...
s were still very expensive at that time. The plug was also quite popular in the demoscene
Demoscene
The demoscene is a computer art subculture that specializes in producing demos, which are non-interactive audio-visual presentations that run in real-time on a computer...
.
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
PC speaker
A PC speaker is a loudspeaker, built into some IBM PC compatible computers. The first IBM Personal Computer, model 5150, employed a standard 2.25 inch magnetic driven speaker. More recent computers use a piezoelectric speaker instead. The speaker allows software and firmware to provide...
; 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.
- Covox Voice Master - speech and music processor.
- Disney Sound Source. A somewhat popular device, marketed by Disney Software in early 1990s, appeared to be a sophisticated Covox-idea based DAC. It consisted of 2 parts: a DAC plugged into printer port and separate amplifier / speaker box. The low price of $14 got the device some popularity. It used external power (ran on batteries) and involved some circuitry to turn it on / off. Sound quality was also superior due to sound filtering schemes used. Games that run on Disney Sound Source should run without problems on simpler Covoxes; however, not all software made for simple Covoxes will run on Disney Sound Source, as it requires additional command bytes to be sent to additional control port to operate.
Features
In its simplest form, Covox received 8-bit, mono signal through the parallel port and produced analog output that could be amplified and played back on loudspeakerLoudspeaker
A loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...
s. Sampling rate
Sampling rate
The sampling rate, sample rate, or sampling frequency defines the number of samples per unit of time taken from a continuous signal to make a discrete signal. For time-domain signals, the unit for sampling rate is hertz , sometimes noted as Sa/s...
was not fixed by hardware means, and theoretically Covox can support any sampling rate. In practice, however, LPT port speed limits make it rather hard to achieve even standard CD-quality 44100 Hz. Another limiting factor compared to real sound cards was the need to use the computationally demanding timer interrupt to play background music, since there was no direct memory access
Direct memory access
Direct memory access is a feature of modern computers that allows certain hardware subsystems within the computer to access system memory independently of the central processing unit ....
available.
Advanced versions of Covox-like devices featured:
- Printer port forwarding connectors — allowed to plug printer into the Covox and use both (playing audio and printing) without reconnections, although not at the same time. Whenever something is printed, loud noise is created.
- Both DAC and ADC converters;
- ADCs with tiny microphone preamplifiers;
- DACs with amplification;
- Sourcing power from serial port;
- Numerous sound-enhancing (hi-fi) features, like filters or equalizers;
- Stereo capability, either by using two parallel ports or one port with switching using strobe (pin #1) and line feed (pin #14) signals.
Compatibility
The Covox plug couldn't directly substitute any of the popular cards of that age (AdLibAdLib
Ad Lib, Inc. was a manufacturer of sound cards and other computer equipment founded by Martin Prevel, a former professor of music and vice-dean of the music department at the Université Laval...
, Sound Blaster
Sound Blaster
The Sound Blaster family of sound cards was the de facto standard for consumer audio on the IBM PC compatible system platform, until the widespread transition to Microsoft Windows 95, which standardized the programming interface at application level , and the evolution in PC design led to onboard...
, Gravis Ultrasound
Gravis Ultrasound
Gravis UltraSound or GUS is a sound card for the IBM PC compatible system platform, made by Canada-based Advanced Gravis Computer Technology Ltd...
, etc), but several games / platforms supported it directly. Notable entries include:
- LemmingsLemmings (video game)Lemmings is a puzzle computer game developed by DMA Design and published by Psygnosis in . Originally developed for PC and Commodore Amiga, Lemmings was one of the most popular computer games of its time, and several gaming magazines gave it some of their highest review scores at the time...
— had special promotional edition named Covox Lemmings, released with Covox sound cards; the game is identical to original game but contains a "Covox" level and seven more additional levels. - Most older Sierra EntertainmentSierra EntertainmentSierra Entertainment Inc. was an American video-game developer and publisher founded in 1979 as On-Line Systems by Ken and Roberta Williams...
games, such as King's QuestKing's QuestKing's Quest is an adventure game series created by the American software company Sierra Entertainment. It is widely considered a classic series from the golden era of adventure games. Following the success of its first installment, the series was primarily responsible for building the reputation...
and Space QuestSpace QuestSpace Quest is a series of six comedic science fiction computer games that follow the adventures of a hapless janitor named Roger Wilco, as he campaigns through the galaxy for "truth, justice and really clean floors"....
series, were available to output the sound to Covox as Disney Sound Source. - Wolfenstein 3DWolfenstein 3DWolfenstein 3D is a video game that is generally regarded by critics and gaming journalists as having both popularized the first-person shooter genre on the PC and created the basic archetype upon which all subsequent games of the same genre would be built. It was created by id Software and...
, Return to ZorkReturn to ZorkReturn to Zork is a 1993 adventure game in the Zork series. It was developed by Activision and was the final Zork game to be published under the Infocom label.-Gameplay:...
, Hare Raising HavocHare Raising HavocHare Raising Havoc is a side-scrolling puzzle adventure game developed by BlueSky Software in 1991 for the Amiga and DOS. Disney Software published the game. It is a spin-off of the 1988 Disney film, Who Framed Roger Rabbit.-Plot:...
(as Disney Sound Source).
Popular DOS-based trackers used on demoscene included Covox support, for example:
- Scream TrackerScream TrackerScream Tracker is a tracker . It was created by Psi of Finland's Future Crew It was coded in C and assembly language. The first popular version of Scream Tracker, version 2.2, was published in 1990...
- Fast TrackerFast TrackerFastTracker 2 is a tracker created by Fredrik "Mr. H" Huss and Magnus "Vogue" Högdahl, two members of the demogroup Triton which set about releasing their own tracker after breaking into the scene in 1992 and winning several demo competitions. The source code of FastTracker 2 is written in Pascal...
- Impulse TrackerImpulse TrackerImpulse Tracker is a multi-track digital sound tracker . It was one of the last tracker programs for the DOS platform. It was authored by Jeffrey "Pulse" Lim, and example music was provided by Jeffrey Lim and Chris Jarvis...
Also, numerous emulator
Emulator
In computing, an emulator is hardware or software or both that duplicates the functions of a first computer system in a different second computer system, so that the behavior of the second system closely resembles the behavior of the first system...
s existed, for example, Virtual SoundBlaster could be used to emulate Sound Blaster on Covox, Covoxer could emulate Tandy 1000
Tandy 1000
The Tandy 1000 was the first in a line of more-or-less IBM PC compatible home computer systems produced by the Tandy Corporation for sale in its Radio Shack chain of stores.-Overview:...
/2000
Tandy 2000
The Tandy 2000 was a personal computer introduced by Radio Shack in late 1983 which used the 8 MHz Intel 80186 microprocessor. By comparison, the IBM PC XT used the older 4.7 MHz 8088 processor, and the IBM PC AT would later use the newer 6 MHz Intel 80286...
music synthesizer on Covox.
Several operating systems have a driver for Covox available for install:
- Windows 3.1xWindows 3.1xWindows 3.1x is a series of 16-bit operating systems produced by Microsoft for use on personal computers. The series began with Windows 3.1, which was first sold during March 1992 as a successor to Windows 3.0...
, Windows 95Windows 95Windows 95 is a consumer-oriented graphical user interface-based operating system. It was released on August 24, 1995 by Microsoft, and was a significant progression from the company's previous Windows products...
, Windows 98Windows 98Windows 98 is a graphical operating system by Microsoft. It is the second major release in the Windows 9x line of operating systems. It was released to manufacturing on 15 May 1998 and to retail on 25 June 1998. Windows 98 is the successor to Windows 95. Like its predecessor, it is a hybrid... - LinuxLinuxLinux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
- MenuetOSMenuetOSMenuetOS is an operating system with a monolithic preemptive, real-time kernel, including video drivers, all written in FASM assembly language, for 64-bit and 32-bit x86 architecture computers, by Ville M. Turjanmaa...
- CSI-DOSCSI-DOSCSI-DOS is an operating system, created in Samara, for the Soviet Elektronika BK-0011M and Elektronika BK-0011 microcomputers. CSI-DOS did not support the earlier BK-0010. CSI-DOS used its own unique file system and only supported a color graphics video mode. The system supported both hard and...
In reverse, DOSBox
DOSBox
DOSBox is emulator software that emulates an IBM PC compatible computer running MS-DOS. It is intended especially for use with old PC games. DOSBox is free software....
allows to emulate presence of Covox (as Disney Sound Source) on a machine without such physical device connected.
External links
- Powering devices from PC parallel port, an article on LPT-port devices, including Covox.
- List of games that support Disney Sound Source at MobyGames.com.
- List of games that support Covox Speech Thing at MobyGames.com.
- A collection of software for Covox, including Windows driver. Covox Voice Master schematics and software. Covox Digital-Analog Converter, a comprehensive Covox history overview.