Re: How is the IIgs beep generated?

[vladitx <vladitx@nucleusys.com>]

On Dec 23, 11:56 pm, "Michael J. Mahon" <mjma...@aol.com> wrote:
> vladitx wrote:
> > Surely you have tried PWM at 15.7 kHz (65 cycles), where no modulation
> > occurs, just slightly inaccurate PWM. Is the carrier that noticeable?
>
> When I was younger, it would have driven me from the room!
> Today, I probably wouldn't notice it.  ;-)

I did quite of PWM on the PC's speaker with carriers in the audible
range, and can't remember being that repulsive. Maybe the magic of the
"useful" 6-bit sound helped (for me), compared to the usual bleeps.

By the way, the 15.7 kHz freq may be already heard from the CRT, so
the listeners should be trained to ignore it to a certain extent. :)

> I've never built a software DAC running at 15.7kHz, partly because
> using it would require resampling all the sound files out there, most
> of which are at 11.05kHz.  It would be pretty easy to try, and the
> extra 19 cycles would certainly be useful.  ;-)

There are command-line tools to do batch resampling for you, like this
one:

http://sox.sourceforge.net/

> One downside is that the maximum variation in pulse width would still
> have to be 32 cycles, since 64 is unattainable in a 65-cycle loop,
> and any other choice results in unequal steps.  The effect would be
> a reduction in maximum volume by 46/65.

If you still decide to give it a try, keep us posted. This sacrifice
is interesting to me at least.

> BTW, there would not be significant PWM inaccuracy, since the
> stretched cycle would always occur at the same point in the loop,
> causing only a slight nonlinearity in transfer function, but no
> beat frequency.

Exactly what I was implying. ;-)