Commander Kinsey wrote:
On Mon, 18 Mar 2019 03:26:19 -0000, Carlos E.R.
wrote:

Possibly one of those adds you get triggered the blast (maybe from your
antivirus?). I have heard that blast on a friend's laptop once, and
scared me ****less. I must say that you guys on Windows get more fun
that us poor lads on Linux :-P

I've never had a bleep like that before. It sounds like the BBC2 test
signal.

History of computing comes to mind...

https://en.wikipedia.org/wiki/PC_speaker

If the sound system is down (driver is not working),
OSes are allowed to use "PCBeep". PCBeep is considered
to be the "backup notification system". If the sound
card goes missing, software is allowed to abuse that.

That is the BIOS "beep" that is used during POST.

The 8254 generates a square wave. Programmers can program the 8254.
The frequency can be changed, by changing the preload constant on the
8254. A sound you don't hear too often from your
PC, is the BIOS "European donkey siren" noise which
is made when the CPU overheats. That sound is made by
reprogramming the 8254 every half a second or so.

The BIOS beeper/speaker has also been tied in the
past, to games. The motherboard speaker can be
used as a 1-bit DAC, and game soundtracks can be
played through it. (A certain era of Macintosh gaming
did this too, and there were probably 200 games
that did the 1-bit DAC thing... The fidelity is
surprisingly good. 1-bit DACs have also been
used in expensive stereo equipment, in case
you thought that nobody would dare try that :-)
To make that work, just crank up the clock rate,
and the 1 bit DAC does a damn good job. The DAC
needs to be followed by a reconstruction filter,
which is what makes it work.)

Sound cards came along later, and were largely optional
at first. Too expensive for the average computer buyer
to be tucking into the machine.

Some sound chips, I believe they have a mono "PCBEEP"
input on the side, for tying the motherboard signal
into the sound chip. This allows using the computer
stereo speakers, to make the PCBeep noise.

In this simply horrible little picture, "PCBeep" logic
input on the sound chip, is next to the STEREO ADC
block. You can see the sigma symbol, which means PCBeep
is wired-OR with the regular sound channel. The PCBeep
is basically "summed" with the BeeGees Greatest Hits
you're listening to :-) Note that most sound implementations
do not bother using that pin any more, because the motherboard
has the PC Speaker or a piezo coin-shaped device onboard
to make the sound instead. The computer is filled
with "legacy support crap" which continues to exist,
wastes a pin, but nobody dare get rid of it.

https://www.mouser.com/images/micros...00_blkdia1.png

In the past, we used to tie the entry of ctrl-G
into a terminal (the "BELL" character), to the PC beep,
If you wrote code, and put a control-G in your printf,
the computer would obediently beep. If you did I/O to
/dev/audio, then a sound would come out of the sound
subsystem speaker (a different speaker or speakers).

That's also the reason, that if you cat'ted a binary
file by accident to the terminal, the terminal would
beep seemingly randomly, because some of the binary values
were the control-G BELL character. So in addition
to crap and "squares" on the terminal textual output,
some of the symbols processed would cause a PCBeep event.

Paul