🚀 go-pugleaf

In article <1992Nov12.023508.13285@tamsun.tamu.edu> rahhelp@rigel.tamu.edu (Ronald A. Huizar) writes:
>
>One problem that I am already see is that the microcontroller I was
>planning to use the MC68HC811E2 can only address about 64K of external
>memory, and we are planning/contemplating storing the message
>digitally. I have not had much DSP, my partner has had more than I,
>but I figure that for the telephone we will need to sample at least
>6000 Hz (since the phone BW is 30-3000, you remember Nyquist don't
>you). For a 1 minute (kinda long I know) message that will require
>about 3 Meg of memeory. To much for the E2. So I know that the
>microprocessors can handle the amount of memory I would need but I did
>want to have build my own computer first.

Well, return to a technique that was common in the old days... bank
switching.  Say you have a 16Mx8 memory bank that you wish to stash your
audio samples in but only a 16-bit address processor to do the stashing.
Well, just feed the other 8 address bits from a parallel output
port.  You then have 256 banks of 64K bytes, selectable by writing the
bank number to the output port.  If you are just storing samples in memory
sequentially it is not a big deal to increment the bank number every time
your 16-bit address counter overflows.

For sampling, your best bet may be a standard telephone codec
(if you get one), which will give you 8K samples/sec.  Nyquist says 2X
the highest audio frequency, but Nyquist has an ideal antialiasing
filter and you don't.

Given the cost of DRAM, it may be reasonable to use a hard disk (an IDE
one should be easy to interface to, SCSI is still reasonable) for voice
storage, or a small DSP for on-the-fly audio compression if you know
an algorithm (I don't).

Markus Wandel
markus@pinetree.org <-- NOT the source of this posting.