Wednesday, September 10, 2014

The Mysterious Covox PC Sound Devices

Covox, Inc. had a niche throughout the 80s and early 90s for making devices that could support some type of speech with home computers.  One of its first products was called the Covox Voice Master.  There was a version for the Apple II and the Atari 8-bit computers and the Commodore 64.

Covox Speech Thing

One of Covox's original PC products was the Covox Speech Thing.  This was a parallel port dongle that functioned as a digital to analog converter.  The 8 data bits of the parallel port would pass through a resistor network and then to an audio output jack.  This device was supposedly released around 1986.  However, it was purely software driven, the CPU had to feed the DAC bytes at a certain sampling rate to allow for convincing digitized sound.  This is a direct drive DAC.  Typically 11kHz was considered the standard for comprehensible human speech, and the resulting performance impact on the IBM PCs of the day was considerably high.  The methods used to create digitized sound on the PC speaker or Tandy 3-voice chip have similar performance issues.  In fact, I do not know of any games supporting this device until 1990.

A true Covox Speech Thing came in at least the two varieties shown here :

The one with the white shell has a 3.5mm and a 2.5mm output jack, the one with a gray shell only has the 3.5mm jack and it is larger, so it is probably an older variant.

A sample of what the Speech Thing sounds like can be heard in this video :

As the Speech Thing is a parallel port device, games that support it will typically allow it to be selected at LPT1-3, depending on which device name the BIOS uses for each parallel port it detects in the system.

Speech Thing Clones

There is nothing special about the Covox Speech Thing, it should consist of purely passive components and the functionality behind the device was widely cloned.  There are schematics available online which you can use to build your own Speech Thing with only a few dollars worth of resistors and a DB-25 connector and shell.

FTL released a version of Dungeon Master with a Covox-style parallel port DAC.  It was called the FTL Sound Adapter.  Rather weirdly for a game designed for mouse input, the adapter had a DE-9 port to plug in an Atari joystick, which presumably used the input lines of the parallel port.  FTL's device could be detected by Dungeon Master, a standard Covox device cannot be detected.

Around the same time (1990), Disney Software released an inexpensive parallel port device called the Disney Sound Source.  The dongle connects to a speaker powered by a 9v battery, and device has active circuitry that is powered from the speaker.  It has several advantages over the Covox, a good low pass filter (no high pitched whines), a 16-byte FIFO that is transfered to the DAC at a fixed sample rate of 7kHz.  It can be autodetected;  The low sampling rate limits the ability of the device to play back music, but it is quite adequate for speech and sound effects.  While Disney Sound Source works with Covox devices, the latter is not true because the DSS has control commands that must be sent for the adapter to work and does not support the variable rates of a dumb device like the Speech Thing.

Covox Voice Master and Voice Master Key

There was two Covox ISA cards, I believe one was the Voice Master and the other was the less functional Voice Master Key (not to be confused with the Voice Master Key System II).  Presumably this is the circuitry of the external Voice Master box put on a sound card.  One of the great benefits of any ISA device over a parallel port device for speech synthesis is its ability to be able to use DMA access to feed its DAC directly with minimal CPU intervention.  This requires the signals on the ISA bus to access a DMA channel and an IRQ channel to tell the program that the buffer is low or empty.  Because 8-bit DMA in the PC is limited to a single 64KB segment, digitized sound typically would fit into 64KB, and if a longer sample was used, more 64KB samples would be fed into the buffer.

If this is the Voice Master card, then it would fit the necessary criteria for DMA usage:

The large chip is an 82C54, a Programmable Interval Timer which contains the counters necessary for DMA usage.  There is also a VMDMA 1.2 silkscreened on the PCB.  The card can use I/O ranges at 22x (default), 24x, 28x and 2Cx, DMA 1 (default) or 3 and IRQ 3, 4, 5, 6 or 7 (default).  Its DAC port is 22F.

This is the Voice Master Key card :

Courtesy of modelrail.otenko

This card has no counter and no DMA capability.  It uses 22F, 24F, 28F, 2CF for its DAC port, selectable via jumper.  The poster of this excellent blog article has gotten the card to work with Covox Speech Thing-supporting games by reassigning the I/O port assigned to LPT1.

Both cards have two M(icrophone) inputs, as does the Sound Master II.  According to a poster for the Sound Master II, one input supports Dynamic microphones and the other input supports line level input or Condenser microphones.  There is an Intsersil ADC to convert the audio input from the microphone from analog to digital.  All output on all these cards is mono.

A second huge benefit of the ISA bus is the ability to support analog to digital conversion.  A standard PC parallel port is not designed to function as an input device.  The standard, unidirectional port only has 5 input lines and some of them are inverted.  (An Atari CX-40 joystick has exactly five inputs, which makes the FTL adapter described above theoretically work without any active components.)  While you can read the port eight times to get the least common multiple, it is generally easier just to read the 8 data bits of the ISA bus.  The Voice Master can record voices.  For non-DMA devices, it can poll the input port at whatever rate the system can support and the available memory will allow.

Covox Sound Master

When the Adlib Music Synthesizer Card was released, the card eventually sparked a great interest in sound cards, mainly for gaming purposes.  Covox Sound Master was one such card and it became available in 1989.  The Sound Master was almost a trial run for the Sound Blaster, but it was not successful or widely adopted in games.  This card contained a Microchip AY8930 music chip that was backward compatible with the popular General Instruments AY-3-8910 3-voice PSG.  It also had a few improvements, but they were seldom used.  The AY-3-8910 and AY8930's registers could be read, unlike the TI SN76496's registers, allowing it to be used as a timer for DMA usage.  The tone registers act as a 12-bit counter and the programmer can read the values, allowing for their usage as crude timers.

The card did support direct drive and DMA fed methods for accessing the DAC.  There is a silkscreened VMDMA 1.3 on the PCB.  Finally, it had two DE-9 ports for using Atari-style joysticks.  These should only be used for true Atari CX-40 style joysticks and Sega Master System pads.  The Sound Master does not emulate a standard gameport, the bits from the joysticks are read via a pair of latches.  It was supported in only a few games, SimCity being the most prominent.

Do not use anything which requires +5v volts like Atari/Commodore Paddles or a  Sega Genesis pad, or you may blow the latch chips.  The card only has an audio output jack, so it cannot record voices.  This is the best photo I have come across of the card (with its PAL chip removed)  :

The card can use I/O ranges at 22x (default), 24x, 28x and 2Cx, DMA 1 (default) or 3 and IRQ 3 or 7 (default).  Its direct write DAC port is at 222, 242, 282 or 2C2.

The Sound Master was not a popular card, the joystick ports were not standard and the music chip was behind the times compared to the FM-synthesis based Adlib, and few companies supported it.  The Covox Sound Master is extremely rare, like the Innovation SSI-2001, only two original cards are known to exist today.

Here are a few samples of AY music from the card, all recorded by a VOGONS user named moturimi1 :

Covox Sound Master Plus and Sound Master II

Covox struck back with two new products in 1991, the budget Covox Sound Master Plus and the Covox Sound Master II.  Neither were particularly successful, and by 1993 Covox was essentially dead.  The Covox Sound Master Plus was an Adlib clone with the ability output digitized sound via direct drive methods. I believe this is a photo of the card :

The Adlib ports can be changed from the default 388-389 to 380-381 and the DAC port from 330 to 338.

The Sound Master II was closer to a Sound Blaster.  It had the OPL2 YM-3812 FM Synthesizer found on the Adlib Music Synthesizer, MIDI in and out via a DE-9 port and a dongle and direct drive and DAC fed digitized sound input and output.  Its MIDI is probably based off the MC6850 ACIA, so it would not be MPU-401 compatible.  It did not have a gameport, which must have hurt its sales.

The Sound Master II has an NEC D71054C Programmable Timer/Counter.  From what I can tell, this chip is compatible with the 82C54 chip found on the Voice Master.  Stamped on one of its chips is VMDMA 3.0.  This is what it looks like :

Like the Voice Master and Voice Master Key, the Sound Master II has a pair of input jacks, marked M1 and M2.  The card can use I/O ranges at 22x (default), 24x, 26x and 28x, DMA 1 (default) or 3 and IRQ 3, 4, 5, 6 or 7 (default).  There are selections for DMA and MIDI IRQs.  The MIDI port defaults to 330-331, but can be changed to 338-339.  The Adlib ports can be changed from the default 388-389 to 380-381.  Its direct write DAC port is at 22F, 24F, 26F or 28F.

The Sound Master, Sound Master Plus and Sound Master II had a 2-pin header on their boards that could be used to mix the input of the PC Speaker with the output from the card, similar to a Sound Blaster Pro and above.  All of Covox's boards typically had a round "Proud to say - Made in USA" sticker on them.

Feature Summary

Device Name Bus Type Music Chip DMA Gameport MIDI Voice Input PC Speaker Input
Covox Speech Thing Parallel Port None No No No No No
Covox Voice Master ISA 8-bit None Yes No No Yes x 2 Yes
Covox Voice Master Key ISA 8-bit None No No No Yes x 2 No
Covox Sound Master ISA 8-bit AY8930 Yes Non-standard No No Yes
Covox Sound Master Plus ISA 8-bit YM-3812 No No No No Yes
Covox Sound Master II ISA 8-bit YM-3812 Yes No Non-standard Yes x 2 Yes

Game Support

Game Name Covox Speech Thing Covox Voice Master Covox Sound Master Covox Sound Master Plus Covox Sound Master II
Alone in the Dark
Music, DAC? Music, DAC
BattleTech : The Crescent Hawks' Revenge

Bad Blood                          
Big Business


Cobra Mission

Conan – The Cimmerian


F-14 Tomcat

Galleons of Glory: The Secret Voyage of Magellan

Music, DMA

Grandmaster Chess

Joe Montana Football

Lemmings (Covox Demo)

MegaTraveller 1: The Zhodani Conspiracy


MegaTraveller 2: Quest for the Ancients

Music, DMA

Pinball Dreams DAC DMA

Pinball Dreams 2 DAC DMA

Pinball Fantasies DAC DMA

Prince of Persia

Music, DMA

Call of Cthulhu: Shadow of the Comet

Music, DAC


SimEarth: The Living Planet


Space 1899


Spirit of Excalibur


Super Jeopardy DAC DAC DAC

The Punisher


Twilight: 2000


Ultima VI : The False Prophet


Vengeance of Excalibur


Where in the World is Carmen Sandiego? 256-Color Version

Music, DMA
Where in Time is Carmen Sandiego

Music AY8930, DMA
Wizardry : Bane of the Cosmic Forge
Wizardry : Crusaders of the Dark Savant
“Music DAC”

Comments on Games

This is not meant to be a truly comprehensive list of game support.  While it has categories for both, Mobygames cannot be trusted to distinguish Sound Master supporting games from Sound Master II games.  For example, it wrongly states that Eye of the Beholder II: The Legend of Darkmoon and The Lost Files of Sherlock Holmes: The Case of the Serrated Scalpel have support for a Covox device, they do not.  Similarly, it claims that Might and Magic III: Isles of Terra has support for the Sound Master, the install program clearly states Covox SMII.  Sometimes the box cannot be trusted, as A-Train's system requirements label distinctly mentions the Sound Master, yet there is no actual software support for the card. 

Most of the information on this list came from this post :

If a game is listed that supports the Sound Master II for music, that really means it supports it as an Adlib card and does not take advantage of any digitized sound features of the Sound Master II.  This is true of the "Covox Lemmings" demo.  

For digitized sound, the Sound Master II and the Voice Master should be identical.  Therefore, I am quite confident to say that Super Jeopardy will work on the Sound Master II using the Voice Master setting.  Fortunately, the game works well with the Speech Thing.

Where in Time is Carmen Sandiego is the only known game to take advantage of the AY8930's enhanced features over the AY-3-8910 for music.  The AY8930 has a 16-bit frequency control for the tone channels, an 8-bit noise frequency control, individual envelope control for each of the three tone channels, 5-bit amplitude control for each channel, a duty cycle control for each channel (to turn a square wave into a rectangle wave) and two registers for noise masking.  The AY-3-8910 has a 12-bit frequency control for the tone channels, a 5-bit noise frequency control, one envelope generator for all three channels and a 4-bit amplitude control.  

For Wizardry : Crusaders of the Dark Savant, while the game has install options for the Sound Master and Voice Master, the game may not actually support either.  When sound is supposed to be played, the timer is programmed but no bytes are written to the card's I/O ranges.  The previous game supported both by direct-drive writes to their respective DAC ports.  The Sound Master II is supported because it uses the same OPL2 direct drive DAC method as the Adlib and Sound Blaster options use.  See my prior post for more details.   Similarly, Transylvania III: Vanquish the Night has install options for the Speech Thing and Sound Master and installs sound files if those options are selected, but the game does not contain code to interact with these devices.

Finally, the floppy version of Alone in the Dark has a mysterious option for the "Sound Master +"  The game only supports FM synthesis, and the options are Adlib, Sound Blaster, Sound Master II and Sound Master +.  For sound effects, it supports "Sound Blaster (DMA)", "Sound Blaster (no DMA)", Sound Master II, Internal Voice Master, the Disney Sound Source.  I assume that "Sound Blaster (no DMA)" is the option for owners of Sound Blasters with a 1.xx DSP, which did not have support for auto-init DMA.  The Sound Master + option gives I/O port selections at 22x, 24x, 28x and 2Cx.  The card described above does not quite fit.  Therefore, either that card is not the Covox Sound Master Plus, (its just the Covox Adlib clone) or Infogrames was misinformed about the card's features.  The driver, when selected, outputs direct drive data to a DAC at 22F.  The driver for the Covox Sound Master II does the same, but the game can detect the presence of a Sound Master II and Voice Master and refuses to let you select those options if it does not detect those cards.  The Alone in the Dark "Sound Master +", if it ever existed, is an Adlib with a direct drive DAC at 22F, 24F, 28F or 2CF.  


The most important devices discussed here are the Speech Thing, which is easy to make and the Sound Master, which is unique both for its music chip and for its music-chip driven DMA method.  Unfortunately, they were rarely used, but are valuable because it is the only representative of the widely used AY-3-8910 chip for the PC (a Deluxe version of the Bank Street Music Writer came with a Mockingboard clone, but that was the only software that used that obscure card.)  Additionally, there are games like Sim City that do not support any other sound cards for their digital sound, so for Sim City its either the Sound Master or a Tandy TL/SL.  Fortunately, like the Innovation SSI-2001 there is some interest in cloning this ultra-rare card.

The Sound Master II and Voice Master are not worth bothering over, a Sound Blaster will always be supported in games 


  1. Well, geez, there was some stuff in this post that even I didn't know. Excellent work!

  2. Hi, with your permission could i use that picture of the Covox sound blaster, i would credit you under the picture of course.
    Btw does the disk itself contain the infamous lemmings demo or just the drivers?

  3. I took these photos from various places around the web, none are mine so I have no permission to give or withhold.

  4. I remember purchasing the "Who Framed Roger Rabbit" game for DOS that came with one of these parallel port sound devices inside. It was a standard resistor based DAC inside, and I remember writing code in Turbo Pascal to drive it.

  5. I have recently acquired a COVOX Voice Master Key (System II) which is an external device that connects to a PC via the parallel printer port. This one appears to be different than the photos I've seen in that mine has a 4" speaker mounted on top whereas the photos on the internet show a small speaker mounted on the front panel. Does anyone have any information as to why there are 2 configurations? Which one came first?

    I've been trying to test it. So far I've applied power and the two LEDs on the front panel light up and I can hear some background white noise from the speaker. I am looking for COVOX program disk for this device.

    So far I've found a copy of the v2.04 disk that was supplied with the PC bus card version of the Voice Master Key, but what I need is v2.04X which directs the I/O to the LPT port. I've searched the internet but cannot find a copy of that software.

    Here's a photo:

  6. I recently acquired a Covox Sound Master Plus and i can confirm Alone in the Dark works with both music and digitized sounds. Despite the port selection does not match the card slelecting the first one works just fine. I believe the program just ignores the port selected and auto detects the card.

  7. Carlos,

    I am not sure whether the auto detection really works with the Plus as released. The game will "autodetect" the Plus if any Adlib or Sound Blaster card is emulated through DOSBox. An Adlib OPL2 chip can be detected when at the proper address by the triggering the timer registers on the chip.

    DOSBox's debugger reports writes to port 22F whenever a digital sound is played. The Sound Master 2 has its direct write port at that location, so Covox may have included it in the Plus for some measure of compatibility with the more expensive SM2. Thus it may be accessible by more than one I/O port.

    The 74HC373 latch on the Plus card would suggest that the DAC acts like a parallel port DAC. The latch can be read on a parallel port card, so that may serve as rudimentary detection but it is hardly infallible.

  8. Hi,
    Covox developer here. I worked with a couple of other guys and we designed all of those boards. I did all of the layouts in ORCAD and even pioneered a circuit board prototyping technique to make double sided boards using a copier and transparency film. This was published in Radio Electronics magazine. Covox was a lot of fun to work with and we had two other employees who were grandsons of the king of Afghanistan and a crack coder Nick who was one sharp cookie. Fun times !!

  9. These Covox things do not work on Win98? I do not get them to work with iplay or glx.

  10. I was the inventor of the Covox products. See what I'm up to now:

  11. Thank you for that :)
    Hopefully I will get the new the dual stereo-covox with DSS-Option as soon as it is fully designed.


  12. "I do not know of any games supporting this device until 1990."
    According to Mobygames, Last Half of Darkness was first released in 1989.
    The copies I tried so far claimed to support PC Speaker, Covox Speech Thing and Sound Master II.

    Anyway, I just thought it was worth mentioning.
    It's been a while since I played the EGA version..

    So perhaps it's better to double check.
    Maybe it didn't support Speech Thing in the 1989 release yet.

  13. Howdy! Even though I don't have the driver disks, I just got my COVOX Voice Master Key going as a COVOX Sound Thing. Also I have a better photo if you want to replace that potato-shot above!

    1. An excellent blog post, that definitely filled a hole in my knowledge about the card. Being able to see the ICs, it is essentially similar to a parallel port except in one respect, the Intersil chip. This appears to be an ADC of some kind which would digitize the speech, which the software would then read and try to compare to the stored voice sample. How well this worked in practice is anyone's guess until you find the disks, but you will never get anything out of the individual who showed you the disk listing. He is notorious in vintage computing circles and definitely believes it is better to receive than give.