Big Mouth was a hardware speech board designed by Martyn Davis around 1984 using the SP0256 chip. The SPO256 is a speech synthesizer chip used in many hardware speech synthesizers of the 8bit era. The SP0256 contains a voice generator, a small microprocessor, and a built-in ROM which contains 16Kbit (2Kbyte) of program code.

A number of different versions of the SP0256 exist. The most common is the SP0256-AL2, where -AL2 means that the built-in ROM contains preprogrammed English allophones. All 59 phonemes of the English language plus 5 pauses of different durations. Each of the phoneme's speech patterns are individually addressable, making the SP0256-AL2 capable of saying anything that can be said in the English language. This is the simplest approach to universal speech synthesis and the speech quality makes for a good robot voice.

Below are Martyn's schematics and a page of allophone work in progress from 1984.

In 2009 the archive team managed to recover a small file from a Deep Thought disk which appeared to be a speech program, Martyn kindly took a look at the file and the result is the listing below.

: announce  ( "I am the Jupiter ACE Computer" )
init ay p3 ae mm
p3 dh2 ax p3 jh
uh pp ih tt2 ax
p3 ey ss ss p3
kk1 ax mm pp yy1
uw1 tt2 er2 p1
;

: phoneme
( phoneme no - )
begin
  portc in 1 and
until
dup 64 or swap over
portb out portb out portb out
;

: init
129 cmd out
( portA, portB, portC, upper=o/p.  PortC lower i/p.)
;

: bb2 63 phoneme ;
: el 62 phoneme ;
: gg2 61 phoneme ;
: yr 60 phoneme ;
: ar 59 phoneme ;
: or 58 phoneme ;
: hh2 57 phoneme ;
: nn2 56 phoneme ;
: ss 55 phoneme ;
: dh2 54 phoneme ;
: ow 53 phoneme ;
: er2 52 phoneme ;
: er1 51 phoneme ;
: ch 50 phoneme ;
: yy1 49 phoneme ;
: wh 48 phoneme ;
: xr 47 phoneme ;
: ww 46 phoneme ;
: ll 45 phoneme ;
: ng 44 phoneme ;
: zz 43 phoneme ;
: kk1 42 phoneme ;
: kk2 41 phoneme ;
: ff 40 phoneme ;
: rr2 39 phoneme ;
: zh 38 phoneme ;
: sh 37 phoneme ;
: gg1 36 phoneme ;
: vv 35 phoneme ;
: gg3 34 phoneme ;
: dd2 33 phoneme ;
: aw 32 phoneme ;
: uw2 31 phoneme ;
: uh 30 phoneme ;
: th 29 phoneme ;
: bb 28 phoneme ;
: hh1 27 phoneme ;
: ae 26 phoneme ;
: yy2 25 phoneme ;
: aa 24 phoneme ;
: ao 23 phoneme ;
: uw1 22 phoneme ;
: dd1 21 phoneme ;
: ey 20 phoneme ;
: iy 19 phoneme ;
: dh1 18 phoneme ;
: tt1 17 phoneme ;
: mm 16 phoneme ;
: ax 15 phoneme ;
: rr1 14 phoneme ;
: tt2 13 phoneme ;
: ih 12 phoneme ;
: nn1 11 phoneme ;
: jh 10 phoneme ;
: pp 9 phoneme ;
: kk3 8 phoneme ;
: eh 7 phoneme ;
: ay 6 phoneme ;
: oy 5 phoneme ;
: p5 4 phoneme ;
: p4 3 phoneme ;
: p3 2 phoneme ;
: p2 1 phoneme ;
: p1 0 phoneme ;

71 constant cmd
69 constant portc
67 constant portb

: h
10 base c!
;

: r
redefine
;

Martyn's schematics as a PDF document.

SP0256-AL2 Data Sheet.

An SP0256 speech chip Emulator for windows. (Runs on Windows XP,Vista,7)

Set of SP0256 Allophone WAV files.