> On Jul 10, 2023, at 12:19 PM, Douglas Taylor via cctalk
> <cctalk@classiccmp.org> wrote:
>
> I'm looking to see if it possible to do something similar. Just blasting raw
> 12bit samples from memory out the D/A board.
> A fine point would be to use the KWV11-C realtime clock board for the sample
> rate control. No interrupts, just polling.
In the case I mentioned I could use the "inhibit bus address increment" feature
of the RC11 controller (and a number of other older controllers) so a long DMA
would send every 16-bit data word to the same bus address (the AA11 data CSR).
That may not be an option for you. If not, you'd have to read from disk while
simultaneously sending to the D/A, which is a simple exercise in asynchronous
I/O programming.
> Harder is taking an existing MPG or WAV audio clip and converting it into raw
> 12bit integers.
> I wouldn't try this on the PDP11, I would do this in Linux, offline, using
> python or octave to take a wide band audio file convert it into a narrowband
> audio file, then resample down to the rate I would use on the PDP11 and
> finally convert the numbers into 12bit integers.
You could certainly downsample if you want to, but as was already observed the
hardware can handle standard audio data rates of 44.1 k (CD rate) or 48 k (the
other common rate) directly. That also avoids the need for much if any
filtering of the output, since the aliases would be above the audible range.
paul
