9 Jul
2023
9 Jul
'23
7:34 p.m.
On 7/9/23 13:46, Douglas Taylor via cctalk wrote:
I have a PDP-11/53 and have just started playing with
an
AAV11-C D/A board. It is a 4 channel D/A convertor with
12 bit resolution.
Can it be used to play an audio bit stream?
Here is simple code used to see if the thing was actually
working:
.title AAV11 D/A test
;
.asect
dbr0 = 170440
.=1000
start:
mov #7777,r0 4096 value to R0
mov #dbr0,r1 first D/A buffer out
loop: mov r0,(r1) transfer value in r0 to D/A out
dec r0 subtract 1 from D/A value
bne loop
br start loop back to start
I was surprised to see that it took ~34 ms to run through
all the numbers from 0-7777, that is about 34 Hz. The
manual says the 'settling time' is 6 microseconds. Is
this fast enough for audio?
How would you convert a modern audio file into 12 bit
integers?
Without DMA, it is pretty hard to do audio. But, if I
calculated it right, 4096 samples /0.34 seconds, that's
120470 samples/second. Of course, with standard 32 K word
address space, you only can get about 1/4 second of audio in
the available memory space, without switching memory space
with the MMU.
Jon