I had an SPO256-based board for my Amstrad CPC!  It was programmed using allophones (datasheet[1]).  AIUI this is a deprecated way of doing speech synthesis, and indeed the results were quite rubbish.  How do modern speech synthesizers work?<p>[1] <a href="http:&#x2F;&#x2F;www.futurebots.com&#x2F;spo256.pdf" rel="nofollow">http:&#x2F;&#x2F;www.futurebots.com&#x2F;spo256.pdf</a>