ISD also have a newish series of ICs - the 33xxx series
which have double the speech capacity per IC. These are
addressable only via an SPI type interface (but you could
implement the correct signals on any standard PIC port). The
older 25xx series used full parallel addressing - this takes
more pins than desirable although you can use modes which
use less pins or ignore lower order address pins if you
don't need small speech block sizes.

I use the 25xx series in communicators that I make for use
by people with speech disabilities. The 2560 gives 60
seconds of telephone quality speech. The 2590 uses the same
core but is clocked slower etc and gives 90 seconds of
2.3KHz speech - this is entirely adequate for message type
recorded voice - many people don't realise it is not
"telephone quality". The 33180 give 3 minutes of speech also
at 2.3KHz and would probably be ideal for your application.
You can get longer recording time versions but quality will
be lower. The 33180 price is about $NZ26 in small quantities
so probably about $US16ish.

From: Bárdos Csaba <cbardos@TERMINUS.INEXT.HU>


>Hi,
>If you would like to get to know about audio compression
>and you want to do it with pic, try microchip appnote:
an643.
...
>On the other hand, I think you don't need to worry about
>audio compression in this case, you can use the isd
devices.
>The isd is an analog storage eeprom.
>You can find more info on the web site: http://www.isd.com.

>>Hi all,
>>
>>I'm thinking of building a digital telephone answering
system. What I
>>really want to know is if there are any good audio
compression
>>algorithms that I can use.
>>
>>I'll be using a PIC processor preferably with a
multiplication
>>instruction. The algorithm can't be too complex because
you need to
>>compress the data in real time (8 bits, say 10kHz).
>>
>>Is this possible or are you better off just storing the
audio data
>>uncompressed? What do you think?
>>
>>Regards, Danjel McGougan.
>>
>>
>