Windows Drivers for CompuPhase Sound - Prerelease
=================================================

Finally you can play music in the background with CompuPhase Sound. For those
who don't know CompuPhase Sound, it is a cheap audio device that connects to
the parallel printer port. Digitized voice and music files can be played back,
recording is not possible.

The hardware comes with drivers for DOS and Microsoft Windows. Until now, the
drivers for Windows until worked in the foreground. That means that the system
is blocked while the audio file is being played through the parallel port.

Recently (today actually), we added a new driver that permits the audio file to
be played back under Windows in the background. The Sound Blaster and other
sound cards have already done so for years, but they use extra memory and some
special hardware to achieve it. The CompuPhase Sound device has no additional
memory, because it would either limit the product to a single fixed frequency,
or make the product too expensive.

So we (the developers of CompuPhase Sound) had to find different ways, and we
quickly found out that Windows was more of an enemy than a friend.

Basically, CompuPhase Sound is a Digital To Analogue convertor (DAC) that is
directly connected to the pins on the parallel printer port. There are also a
couple of other devices that work the same way as CompuPhase Sound (for example
the Covox Speech Thing). This driver can also be used for those products. You
can also build one yourself with a handfull of resistors, using the following
circuit:

          signal   pin        20k   20k
          D0       2      >İİĿ
                              20k  10k  
          D1       3      >İĴ      
                              20k  10k  
          D2       4      >İĴ      
                              20k  10k  
          D3       5      >İĴ      
                              20k  10k  
          D4       6      >İĴ      
                              20k  10k  
          D5       7      >İĴ      
                              20k  10k  
          D6       8      >İĴ      
                              20k  10k  
          D7       9      >İĴ      
                              20k  10k     100nF
                                  |Ĵ > TO AMPLIFIER
                                   10k  
          GND      20     >> 0 volt

With this circuit attached to you printer port and the driver in this package,
you can have decent audio quality that plays in the background.

A few notes about the circuit:
- The cheap resistors are the 5% precision types, but 1% precision sounds
  better and gives less noise.
- Don't use 22k resistors. Although they are much more common, 20k sounds much
  better than 22k.

So now you have the driver and the circuit to make yourself. Why would you need
CompuPhase Sound? Well, we think our product improves on the circuit above.

- One problem with the circuit is that the amplifier needs to have a high input
  impedance (500k or more). If it does not, sound is distorted and audio
  quality is low. CompuPhase Sound comes with an amplified speaker box that is
  optimized to the circuit (we use a slightly different circuit, though).
- The amplifier should also filter frequencies above a certain boundary, to
  avoid a type of distortion called "aliasing".
- CompuPhase Sound is cheap (but not yet available everywhere). If you build
  your own circuit plus amplified speaker box, you may be spending more money.
  Prices are NGL 95.= (excl. VAT) in the Netherlands and FF 300.= in France.
- You may only use this driver on a personal basis. You may not sell it or
  bundle it with a software or hardware package.

        ITB CompuPhase                  3P Informatique
        Brinklaan 74-b                  4, Rue Ren Barthlmy
        1404 GL  Bussum                 92120  Paris Montrouge
        The Netherlands                 France

        voice: 31 2159 32961            voice: 33 1 4092 0807
        fax:   31 2159 39293            fax:   33 1 4092 1211

        CompuServe: 100115,2074


Final note:

This software is a prerelease. It contains several known bugs. A newer version
is uploaded as soon as the bugs are corrected. If you find any bug that is not
listed below, feel free to contact us on CompuServe.

- The manual speaks of DOS drivers. While these drivers exist, they are all
  being revised for compatibility with VESA AI. Uploading them now would be of
  little use, because only programs written specifically for CompuPhase Sound
  would be able to use them. Most of the sections concerning the DOS drivers
  was deleted from the manual.

- Playing in foreground (select "exclusive playing" in the driver setup)
  sometimes plays back at an incorrect pitch. We must have broken something at
  the last minute.

- When exiting Windows, the last sound is cut off before it has completed. It
  appears Windows sends us messages in an unexpected order.

