Changes
* [[SP0256 Allophones]]
* [[SP0256 Pin-Outs]]
* [[SP0256 on Printer Port (DIY)]]
== Voice Generator==
The voice generator relies on the Amplitude, Pitch, F0..F5, and B0..B5 registers, which are processed like so:
Another important register is the Repeat counter, which indicates when the next opcode shall be executed (and which may then load new values into the above registers).
== Sample Rate and Repeat Timings==The SP0256 is (usually) driven by a 3.12MHz oscillator, and it uses 7bit PWM output. So the sample rate should be , which is clocked at 3.12MHz/2, to obtain a 10kHz sample rate, the chip issues some dummy steps with constant LOW level additionally to the 128steps needed for 7bit PWM, probably further divided by two:making it a total number of 156 steps per sample.
Sample Rate = 3.12MHz/256 2/156 = 1210.1875kHz 0kHz ;82.051ns 100us per sample
Which means one sample is 82.051ns 100us long, that value multiplied by 64 or 91 gives the following timings per repeat:
== Amplitude/Pitch/Repeat==
The 8bit amplitude register defines the volume in floating point form,
Note that (aside from noise) the AL2 ROM uses only one pitch value: 5Bh aka 91 decimal (meaning that all vowels are using the same base frequency, and they differ only by using different filter settings).
== Amplitude/Noise/Repeat==
Noise is activated when setting pitch=0. The timings are then same as when pitch=64, but instead of outputting HIGH and NULL levels, the hardware does now randomly output HIGH or LOW levels, for example, pitch=0 and repeat=5:
The exact random algorithm is unknown (probably some shift/xor stuff?), the random levels seem to be output on each sample (not only on the first sample of a repeat). Like normal pitch, the noise is passed to the 6 filters.
== Pause/Repeat==
The pause command sets amplitude=0. The timings are then same as when pitch=64, but the output is always NULL, for example, pause and repeat=5:
Pause does reset the filters to 0, so the silence is not affected by filters.
== Digital Filters==
As shown above, the amplitude/pitch/noise output is passed through six digital filter stages (using the F0..F5 and B0..B5 registers), each stage looks like so:
Above shows only positive values for index 0..127. Values for index -1..-128 should be 0..-511, or maybe -9..-512.
[[Category:Music and sound]]
