Getting Started
Start the program by typing:
RUN
Play the keyboard. There are two rows of playable octaves.
Use the num-pad to change the settings. There's vibrato, distortion, different octaves and pulse-widths, as well as a "drum mode".
Use the RUN-STOP button to stop the program from running.
Keyboard Note Layout
The lower octave starts at z as the note C, and proceeds with s and d as C# 9c sharp) and D# respectively.
The upper octave starts at q as the note C, one octave above the lower z octave, and proceeds up the scale. OFF RVS and @ are also notes, B and Bb (b flat) respectively.
Changing Effects
The number pad on the Commodore PET 4032 is setup to change the sound.
Vibrato
Starting at the bottom, the . (period or decimal) toggles the vibrato effect on and off. The button on the right, the - (minus) increases the depth of the vibrato effect. The button on the left, the 0 (zero) key, decreases the vibrato effect. Any setting above 1 or 2 is usually to great a difference in pitch and causes a more laser-gun like sound.
Pulse Width or Octave
The pitch, octave, or pulse width is set to the default of 15 by pressing 2 on the number pad. The 3 on the left increases this value, and the 1 on the left decreases it. There are 255 possible values. This relates to the way the PET generates sound, and the value displayed is the value passed to whatever part of the memory is mapped to the shift register that ends up controlling the sound. Since sound was originally a hack on the PET, this setup is doesn't seem to make any logical sense, at least musically. I just hit keep changing the value to whatever I like and stop there.
Maybe this is something that could be different in the future. Since PetSynth automatically plays the last played note when you're changing effects, you can press a note you want, then toggle the effects on or off, or change the setting, and you'll hear the last note. So you can play interesting things if you use this musically. For example, if you hit the root note of whatever chord the song you're playing to is on, you can press the 1 and 3 keys back and forth in time to create an interesting back and forth sound, depending on what you're toggling.
Note Length
Unlike other keyboard sounds, where the note length is determined by how long you hold the key down, the PetSynth instead allows you to set a specific note length. This is because I couldn't figure out which registers to read to determine when a key is released. It's also interesting in other ways.
The 5 key sets the note length to the default value of 250. This is the actual number of loops the program performs to count out the note length. Press the 6 and 4 keys to lengthen or shorten the note length respectively.
I find that when doing drums sounds, a shorter length or duration of note sounds more drum-like.
The 8 key toggles the distortion effect on and off. The 9 and 7 keys lengthen and shorten the distortion time respectively, just like the length does. I find that the default value of 1 is the only real setting that seems to have an effect on the sound at all. Based on the way it was programmed, I may change this in the future to have a more dramatic effect, but for now, you'll probably notice that 1 or maybe 2 is best. Follow your ear.
Please note, at this time, the vibrato and distortion effects don't work together. If you turn them on at the same time, only the distortion is working. I may change this too at some later time.
Drum Effects
Finally, the drum effects. The PET doesn't have a proper sound chip, therefore, it also doesn't have a noise generator. The drum effect is caused by rapidly changing the pulse width or octave (it's the same setting) which seems to have an intersting effect on the sound. Additionaly, changing the pulse width or octave setting also seems to create a breif "pop" in the sound.
All this ends up sounding, when you change the note length to about 100 or so, very drum-like. At least, from a 1970's computer being used to create drum sounds perspective. It's not like the Atari 2600 or Commodore 64 noise sound. It's unique.
Someone could program a digital to analog routine to take advantage of this. Since something similar has been realized for the Commodore 64, such as demos, MSSIAH, as well as the Apple II, such as RT.Synth, it's possible to do the same for the PET, perhaps maybe even porting some of the RT.SYNTH 6502 assembler to the PET.
Notes off
Press the space bar to turn off playing of notes. In drum mode, or noise mode, any keys that don't make sounds, such as the space bar, make a softer noise that's always the same. This is purely an accident. It's the sound of just the pulse width or octave changes, all while the note value is at 0.
Repeating the Last Played Note
By pressing any of the cursors keys or delete key, the last played note will repeat itself, due to the key repeat function of the keyboard. These are the only keys that do this. This might change in the future.
Arpeggiations
PetSynth doesn't support a specific arpeggiation feature, however, the nature of the keyboard hardware and software allows something similar.
For example, press the c key (this plays the E note) and then hold that key down. The note stops playing. While holding it down, press the m key (B note) and hold it down. The note plays as expected. However, if you keep the c key pressed, while you release the m key, the c key is triggered again.
To create the arpeggiation style effect, press the hold the c key while rapidly pressing the m key. You should hear the a arpeggiated E fifth. This works if you switch to the n, back to the m, then to the , (comma) keys, pressing rapidly, all while holding the c key (E note).
However, because of the hardware setup, certain keys have a "priority" of sorts over other keys. In the example above, the m key takes a higher priority over the c key (E note). If you press and hold the m key first, pressing the c key does nothing.
Using the example above, the e key (the upper octave E note, coincidentally) takes a lower priority over the c key (the lower octave E note). If you press c first, pressing e does nothing. However, pressing e first lets you press c second, and allows the rapid playing arpeggiation effect to work.
Ending the Program
Just press the RUN STOP key to end the program. If that's super easy or annoying, I may change that in the future, but for now it's logical, easy to remember, and hasn't been a problem for me.
I hope you enjoy it!