'===========================================================================
' Subject: PC SPEAKER DIGITAL SOUND           Date: Unknown Date (00:00)   
'  Author: Edward Schlunder                   Code: TEXT                   
'  Origin: PC,SPEAKER,DIGITAL,SOUND         Packet: SOUND.ABC
'===========================================================================
> I'm trying to write some code that plays audio files (VOC, SND, etc.)
> through  the PC speaker.  The audio data I'm working with is 8 bits,
> and the PC speaker is only a one bit device.  Here's what I'm doing:

      Nice try, but the PC's Internal Speaker can do about 6 bits. It
just takes a little figuring out.. If you set up the PIT correctly, it
can be really easy! Here, let me help you..

      I'm writing a book on sound and stuff. It will be really cool.
It's gonna include information on programming all the sound cards
available, such as the SB, AdLib, and GUS. It's also gonna talk about
doing some stuff on the Internal speaker, so I've been writing a section
on getting different volumes on the PC's Internal Speaker. The book
isn't finished by far, but, the part about playing digital sound on the
internal speaker is *almost* finished. I'll post this pre-release of
BWSB for you..

       ___O_/____________________| SNIP |_____________________O_/___
          O \                    | HERE |                     O \

   > Volume <

      Some programmers have discovered that they can create different
   volume settings on the speaker. This is done by giving the speaker
   +5v and then quickly giving it 0v. Because the speaker is rather slow
   to responding to the power (when compared to the computer's logic),
   it does not go fully out, like it should when given +5v. By making
   the speaker go out only so much and then pulling it back in, we can
   have different volumes by changing the amount of time that the
   speaker can move.

      This sounds like a very timely task, and it is, if you program the
   speaker directly. Using the PIT to drive the speaker makes the task
   MUCH easier (not to mention much easier to program!).

      To do this, we must setup the PIT to do some certain little
   things. To set it up for doing different volumes, we do the following
   (Basic source code):

      OUT   &H43, &HB6                 'Setup to make no sound
      OUT   &H42, &HFF
      OUT   &H42, 0

      OUT   &H43, &H90                 'Setup to interrupt on terminal
                                       'count

      OneShot = INP(&H61) OR 3         'Puts the speaker in one shot mode
      OUT   &H61, OneShot

      After this has been done, any values sent to port 42h tell the PIT
   what volume the speaker should be at. The speaker, however, has an
   upper limit to the volume which isn't very loud. The upper limit is
   64, any values above that can cause distortion.

      Lets see what this is doing. The values that you give to port 42h
   are really telling the PIT how long to delay in between toggles of
   the speaker. With really small delays, the speaker is moved back in
   before it can get totally out. This is a quiet noise. With larger
   delays, the speaker can go completely out before being pulled back
   in. This creates a loud noise.

      Now, if you specify a large volume level, the speaker will go
   completely out, but the PIT will still be delaying.. The PIT will
   eventually pull it back, but obviously, this will be no louder than a
   value between 64 and 255. Infact, it could be softer, the extended
   delays would slow down the number of vibrations it makes, making less
   noise (I'm not sure about this idea).. This the distortion I had
   talked about earlier.

      After you are finished using the speaker in different volumes
   (usually at the end of your program), you should set the PIT back the
   way it was before, so that other programs will run correctly. If you
   don't do this, any tone made by an other program will continue on,
   never stopping because of your program. This is very annoying for the
   user, you have to reboot usually to make the tone stop.

      This is what is necessary to reset the PIT:

      OUT   &H43, &HB6
      OneShot = INP(&H61) AND &HFC
      OUT   &H61, OneShot