SP0256 Measured Timings

Here are some measured timings for the SP0256-AL2 speech chip. Mainly here to confirm and understand how it works. All timings were measured by gerald, on a Amstrad SSA-1 with 3.12MHz ceramic resonator.

PWM Output

This image shows the PWM output. The PWM is clocked at 3.12MHz/2 (so one step is circa 630..640 µs).

• Normally, 7bit PWM should consist of one "packet" with 128 steps. However, this seems to be broken down to four "quarter-packets" with 32 steps. This technique reduces the PWM noise from 10kHz to in-audible 40kHz.
• The image shows one such "quarter-packet" with 32 steps (actually 33 steps, not sure why, so let's ignore that). Additionally, there are some dummy steps with constant LOW level inserted between each quarter-packet, making each quarter 39 steps long. This is done to achieve a sample rate of 10kHz (a full packet is 156 = 4*39 steps, so sample rate is 3.12MHz/2/156 = 10kHz).
• For whatever reason, the quarter packets aren't always 39 steps long, instead, they vary from 38 to 40 steps. Anyways, better let's ignore that, too.

Allophone Lengths

This table shows the allophone lengths in milliseconds.

• spec = Timings from original datasheets (these values are totally wrong)
• calc = Timings calculated from 10kHz sample rate and the pitch/repeat values in the -AL2 ROM
• min/avg/max = Timings measured on real hardware (Amstrad SSA-1)

The min/avg/max values are slightly higher than the calculated values. This is probably because the SP0256 executes "NOPs" (with repeat=1 and pitch=unchanged) while in standby mode, and refuses to start a new allophone until it has finished the "NOP".

num name      spec   calc     min     avg     max
00  PA1       10.0    6.4    6.66   10.05   12.80
01  PA2       30.0   25.6   26.71   31.33   32.37
02  PA3       50.0   44.8   46.05   50.12   51.39
03  PA4      100.0   96.0   97.81  101.72  103.24
04  PA5      200.0  198.4  200.50  204.11  206.69
05  /OY/     420.0  291.2  293.06  297.24  299.12
06  /AY/     260.0  172.9  174.81  175.98  176.96
07  /EH/      70.0   54.6   56.32   57.05   57.94
08  /KK3/    120.0   76.8   78.82   79.89   81.05
09  /PP/     210.0  147.2  148.91  153.20  155.04
0A  /JH/     140.0   98.4   99.15  103.24  105.45
0B  /NN1/    140.0  172.9  174.89  175.81  176.92
0C  /IH/      70.0   45.5   46.80   47.73   48.38
0D  /TT2/    140.0   96.0   98.85   99.47  100.29
0E  /RR1/    170.0  127.4  128.37  132.63  134.44
0F  /AX/      70.0   54.6   55.55   57.01   57.97
10  /MM/     180.0  182.0  184.14  185.08  186.15
11  /TT1/    100.0   76.8   78.47   79.92   80.93
12  /DH1/    290.0  136.5  137.33  141.89  143.54
13  /IY/     250.0  172.9  174.31  175.74  176.46
14  /EY/     280.0  200.2  201.75  202.85  203.69
15  /DD1/     70.0   45.5   46.95   48.12   49.14
16  /UW1/    100.0   63.7   65.20   66.21   66.78
17  /AO/     100.0   72.8   74.09   75.46   76.50
18  /AA/     100.0   63.7   64.51   65.72   67.49
19  /YY2/    180.0  127.4  128.82  129.93  131.25
1A  /AE/     120.0   81.9   83.35   84.44   85.51
1B  /HH1/    130.0   89.6   91.78   92.79   93.78
1C  /BB1/     80.0   36.4   37.44   41.30   43.08
1D  /TH/     180.0  128.0  130.04  130.96  131.91
1E  /UH/     100.0   72.8   73.53   77.48   79.34
1F  /UW2/    260.0  172.9  174.95  175.91  176.66
20  /AW/     370.0  254.8  256.68  258.09  259.14
21  /DD2/    160.0   72.1   73.42   74.94   76.17
22  /GG3/    140.0  110.5  111.86  113.73  114.78
23  /VV/     190.0  127.4  128.55  130.10  131.48
24  /GG1/     80.0   72.1   73.55   75.05   75.85
25  /SH/     160.0  198.4  201.15  202.43  203.59
26  /ZH/     190.0  134.1  135.23  139.72  141.61
27  /RR2/    120.0   81.9   82.45   87.02   88.53
28  /FF/     150.0  108.8  111.12  112.07  113.32
29  /KK2/    190.0  134.4  136.08  140.64  142.21
2A  /KK1/    160.0  115.2  116.63  121.24  122.82
2B  /ZZ/     210.0  148.6  149.79  153.20  155.85
2C  /NG/     220.0  200.2  202.19  203.01  204.00
2D  /LL/     110.0   81.9   82.75   84.16   85.52
2E  /WW/     180.0  145.6  147.85  148.41  149.52
2F  /XR/     360.0  245.7  247.67  248.61  249.59
30  /WH/     200.0  145.2  147.29  148.30  149.80
31  /YY1/    130.0   91.0   92.79   94.04   94.87
32  /CH/     190.0  147.2  149.15  150.62  151.77
33  /ER1/    160.0  109.2  109.87  114.27  116.10
34  /ER2/    300.0  209.3  211.77  212.71  213.70
35  /OW/     240.0  172.9  174.74  176.24  177.05
36  /DH2/    240.0  182.0  183.81  184.58  185.83
37  /SS/      90.0   64.0   65.48   66.66   67.66
38  /NN2/    190.0  136.5  141.65  142.48  143.68
39  /HH2/    180.0  126.0  128.30  128.99  130.16
3A  /OR/     330.0  236.6  238.56  240.04  241.20
3B  /AR/     290.0  200.2  202.69  203.70  204.72
3C  /YR/     350.0  245.7  247.68  249.01  250.33
3D  /GG2/     40.0   69.4   71.15   71.96   73.17
3E  /EL/     190.0  136.5  138.22  139.21  140.52
3F  /BB2/     50.0   50.2   51.92   53.17   54.10