This is one of those "Rorshach ink-blot tests" for engineers, I think.  ;-)

Software guys will suggest lookup tables, PWM, external DACs, etc.,
while hardware guys will typically suggest some sort of filter network,
sometimes based on PWM, sometimes on a triangle wave, or, my
personal favorite for this application, filtering out the first harmonic of
a square wave.

That may prove a little tricky, since at such a low frequency your 3rd
harmonic isn't going to be TOO far away, but you should be able to
attenuate it below audible range fairly easily.  See FilterLab for details.

The other thing I'll mention is that you may want to leave the signal
running full time.  Starting and stopping an audio signal can lead to a
very audible POP at the beginning and end.  TI makes a couple of
audio amplifiers (unfortunately SMT only), the TPA 122 and 152,
which have in-built pop reduction.  Hook those up as your output
stage and connect up to the MUTE lead on the chip, start your PICs
PWM at 1300 Hz, and away you go!

Mike H.

PS- A more saavy audio/analog guy may know an easier way to
lose that popping effect, but that's not me!
>Hi,
>
>I need to generate a 1300Hz ish sine wave pulse, from a pic, that I can
>plug
>into a tape recorder's line in jack to log.
>
>Obviously, it's fairly easy to get a 1300 Hz square wave, but what can I do
>to simply and easily smooth this out a bit, so it's reasonably close to a
>sine wave?
>
>Any pointers appreciated
>
>Thanks
>
>Jon
>
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