Este fue el primer intento, bastante mugriento, aunque funcionó bien de todos modos.



Después conseguí hacerlo sin quemar el soporte de plástico.

The Basic code is a spaghetti mess and the user interface is not very friendly, but it works. You'll see some gargabe characters I've been using as a kind of visual debug to pin down what's going on in the machine language routines. Some day I'll clean it up. The machine language code is pretty optimized and clean though.

Once the program is running, please be careful when entering data. Values out of the range 0-255 aren't checked for validation when you enter them and will cause an ILLEGAL QUANTITY ERROR. In that case, you'll have to restart the program.

At any rate, all SID's paramaters can be edited and you can save and load patches.The keyboard can be divided in two parts, each of which can carry one or two of the 3 SID voices. If not split, the whole keyboard carries the 3 voices (full polyphony). There are 6 different modes (see below).

 Polyphony modes and keyboard split
(MIDI CCs or push buttons)

There are three functions you can control with control changes from your MIDI controller or with push buttons from the Arduino circuit.

1. Switches ciclicaly among the 6 modes: 1 > 2 > 3 > 4 > 5 > 6 > 1. This is CC #97 or the push button connected by the white wire.
2. Shifts ciclicaly the keyboard's split point, one octave to the right: C4 > C5 > C6 > C2 > C3 > C4 [verificar]. Once you reach the rightmost point, the next position will be the leftmost one again. This is CC #96 or the brown wire.
3. Toggles left / right the two parts of the split keyboard. This is CC #66 or the blue wire.

If you want to use other control changes, you can search for 97, 96 and 66 in the Arduino sketch and change them for other values.

The 6 polyphony modes

1		3 independent voices/oscillattors: Full polyphonic, you can play up to 3 notes at the same time all along the keyboard.
2		Voice 1 on one half of the keyboard, voices 2 and 3 coupled on the other half: you can play one note on each half of the keyboard. In one half of the keyboard, voices 2 and 3 are triggered at the same time when you press a key; you can detune the voices or synchronize or ring modulate voice 3 by voice 2.
3		Voice 1 plays "pseudochords" on one half of the keyboard, voices 2 and 3 are played independently on the other half. The pseudochords allows you to play up to four notes at the same time on one part of the keyboard; those notes are played actually like an arpeggio, and when played fast enough, they sound almost like a chord (a well known effect you have heard in many games).
4		Voice 1 plays "pseudochords" on one half of the keyboard, voices 2 and 3 coupled on the other half.
5		Voice 1 on one half of the keyboard, voices 2 and 3 not coupled on the other half. This is similar to mode 1, but you can use different sounds in two separates parts of the keyboard (multitimbral). Or you can use the same timbre in both halfs, but making sure that the notes on one half never override the notes being played in the other half.
6		3 voices coupled. This is a monophonic synth with 3 oscillators. You can detune any of them, synchronize or ring modulate to each other.

Once you run the program, you will be prompted if you want (Y/N) to read the data for the machine language code and the tables used by it. You have to select "Yes" the first time. If for some reason you have to restart the program without having turned the computer off, you can bypass this by selecting "No" and save some time. You might need to restart the program if you have entered a wrong value when editing a patch or pressed Run/Stop by mistake. The program is still in development and it's not very user friendly in this sense.

Things that can't be done (yet) and bugs that I'm going to fix in future versions:

• Only the five central octaves can be played on the keyboard (C2 - C6). You can tune the oscillators one octave higher or lower, so you can reach C1 and C7, but still only by playing "physically" the five central octaves. I have only 4 octaves on my MIDI keyboard, so I haven't actually checked what happens when playing on a larger keyboard; you might hear weird tones under C2 and above C7.
• No vibrato. Unlike the pulse width and the filter cut off point, which can be swept up and down by routing them through a LFO, the note pitch can't be modulated this way.
• The oscillators can be detuned up to half tone up or down. A finer tuning, under half tone, is not possible yet.
• Although each voice has its own independent LFO to control the pulse width, all voices are routed through the same LFO at the moment.
• No paramaters can be controlled with the pitch wheel or the knobs on the MIDI controler.
• No touch sensitivity (note speed).
• Some parameters [cuáles] can't be saved. When you load a saved patch, you have to set them manually.

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Once you RUN the program and all data are read, the main menu will appear:

The numbers 1, 2 and 3 in the middle of the screen stand for the three voices.

The number highlighted in white is the voice currently selected, which can be changed by pressing the keys 1, 2 and 3. Some parameters can be edited only for one voice each time, so you have to select first the voice you want to edit. These parameters are PW ENV LOOP (option D), ADSR (option G) and the oscillator tuning, located top right:

With the cursor up/down key you can increase or decrease the pitch by 12 semitones (one octave) and with the right/left key 1 semitone more or less.

This main screen contains the only menu you'll use to edit all settings. At this point, you can perform a first sound test: by pressing the space bar key, you'll enter the play mode. You'll see some charachters rapidly changing on screen, and if you press keys on your MIDI keyboard, you should be able to hear the notes. The default mode is polyphonic, so there must be possible to play up to three notes at the same time. By pressing the Return key you'll be back at the edit mode; any character should stop changing on the screen.

By pressing the keys A to K you can access the following options. Only B to J are visible on the menu.

A	Wave tables and arpeggios editor (see option K)	This is the most complex section, containing several parameters explained below. The three upper rows 54276 ($D404) Voice 1    54283 ($D40B) Voice 2  54290 ($D412) Voice 3 are the waveforms editor, wich basically represents a sequence of four states in the registers 54276, 54283 and 54290. These SID's registers determine the oscillators' waveforms, as well as the synchronization and the ring modulation effects and the gate state. Each character stands for a state of the register at a time unit. All 8 bits can be switched on/off independently.   The numbers 1 to 8 stand for the keys you have to press, but when I refer to bits they are numbered from 0 to 7 and from right to left. Function Noise Square Saw tooth Triangle Test Ring modulation Synch. Gate Key 1 2 3 4 5 6 7 8 Bit 7 6 5 4 3 2 1 0   The first 4 states are swept in a loop from left to right during the ADS phase (when you press a key in the MIDI keyboard) and the last 4 states are swept the same way in the R phase (when you release the key and the sound starts to fade out). By combining different waveforms within the same phase, distorted and metallic sounds can be generated.   The three lower rows are the arpeggios editor.
B	Arpeggios speed	Sets the speed at wich arpeggios are swept. Arpeggios can be set as fixed in the arpeggios editor or as pseudochords in real time, as you play several notes simultaneously (keyboard mode 3 and mode 4). Valid values are in the range from 1 to 128.
C	Pulse width sweep speed, square LFO on/off	This synthsizer uses two software generated LFO to modulate the cut off frequency and the square waveform pulse width, respectively. Although the SID can use the third oscillator's output to hardware generate an LFO, I left out this built-in LFO, as it works at the price of giving up the sound of voice 3. Polytimb 64 actually features three independent LFOs to modulate the PW in each of the three voices, but for the time being I'm using the same LFO for the square waveform of all voices. The first value determines the speed of the ascending sweeping through a PW defined range (see option D). The second value does the same for the descending sweeping. This is like routing the PW through a LFO.   Enter "1,1,0"  Enter "2,2,0"      Enter "1,2,0"  Enter "8,1,0"
D	Pulse width envelope/loop	This controls the LFO as well as a kind of primitive envelope for the PW by determining the starting, highest and lowest PW levels (first, second and third digits, respectively). The fourth digit sets the initial direction of the PW sweep (1 = ascending, 0 = descending) and the fifth digit sets if the PW stops sweeping once it reaches the lowest/highest point for the first time (0), if it stops after reaching a second lowest/highest point (1), or if it keeps on sweeping up and down indefinitely between the lowest and highest levels. For the first three digits the range is between 0 and F: for the sake of simplicity only the most significant byte of the PW can be selected by the user. However, the PW sweeps all along the least significant byte (at the speed defined in option C). In this settings, the values are entered with keys 0 to 9 and A to F, shifting the selected digit left and right with the cursor keys. Hitting the Return key confirms the selected values and T copies the selected values to the PW envelopes of all voices. Enter "5C210" The third digit, "2", is not relevant  in this example. Enter "5C211" Enter "5C212" Enter "AD302"
E	Filter cut off sweep speed, square LFO on/off, filter resonance	This is the same as option C but for the filter cut off frequency. In addition to the three values explained in (C) you have to enter here a fourth value between 0 - 15 for the filter resonance. For instance, "1,1,0,15" stands for 1 sweep speed up, 1 for sweep speed down, no square LFO and 15 (maximal) resonance.
F	Filter cut off envelope/loop	Same as option D, but for modulating the filter cut off frequency. Since the SID cut off frequency is 11 bits long, the maximal value you can enter here for the first three digits is 7 instead of F.
G	Volume ADSR	This is the amplitude envelope generator. Unlike options D and E, this is a hardware feature of the SID: registers 54277 (attack/sustain) and 54278 (sustain/release) for oscillator 1, registers 54285 and 54286 for oscillator 2, and registers 54291 and 54292 for oscillator 3. The values are entered by pressing the keys 0 to F; the left and right cursor keys shift the selected digit, the Return key confirms the entered values and the T key copies them to all three voices. There is a known bug in the SID chip, which prevents, for certain ADSR values, the attack to start properly, so you can't hear any sound when you press a note key. More about this here.
H	Save patch
I	Load patch
J	Glide speed	This sets how fast (1 = fastest, 255 slowest) a note's pitch increases or decreases when you press a key on the keyboard. Three values separated by comma must be entered, one for each voice. Very slow glide speeds let hear "steps" along the pitch variation, but for most "normal" speeds you'll hear a continuous, smooth glide. In order to the glide effect to be effective, it has to be set to one of the three ON modes. With the keys F1 (voice 1), F3 (voice 2) and F5 (voice 3) you can sequentially select: @ Glide off A Glide on downwards: starting from an octave lower than the note played on the keyboard and gliding up to the actual note. B Glide on upwards: starting from an octave higher than the note played on the keyboard and gliding down to the actual note. C Glide on from the last note played. In this mode, with F7 you can set wheter the glide from one note to another will take place from different parts of the keyboard (A) or only within one of the split parts (@), provided that you are using one of the split keyboard modes (2, 3, 4 and 5)
K	Wave tables speed (see option A)	Enter a delay value for each voice, separated by comma, to determine how fast the sequence of waveforms is read in a loop (the higher, the slower). More about this here.
L	Enter POKEs manually	[Funciona, pero lo vamos a dejar en blanco.]

Waveforms / Arpeggios editor

Once you press the A key in the main menu, you enter this area, with the cursor on the middle of the top row.

Here you can edit a number of paramaters with the following keys:

• General
  • Cursor keys: moves one space up, down, left or right within the central area. If you go out on a side, you'll enter from the other one.
  • Commodore Key + C: Copy the value of the current position.
  • Commodore Key + P: Paste a value into the current position.
  • Shift + 1 to 6: Copy the row you are at to another row (1 - 6)

• While being at one of the 3 upper rows (waveforms)
  • Keys 1 to 8: switches on/off one bit of the 54276/54283/54290 registers for the time position you are at in the row's sequence.
  • Commodore Key + Keys 1 to 8: switches on/off one bit of the 54276/54283/54290 registers at all time positions in the row's sequence.
  • Keys F1, F2, F3 and F4: selects at which position (1, 2, 3 or 4 in red below) the row's sequence loop is restarted; the same value is used for all voices. For instance, you can have a triangle waveform at the first position and square waveforms at positions 2, 3, 4. Then you select 2 (F2) for the loop restart. When you press a key in the MIDI keyboard, you'll hear a brief triangle waveform and then a continuos square waveform. The waveform sequence is read as: 1, 2, 3, 4 -> 2, 3, 4 -> 2, 3, 4 -> etc. With the K key in the main menu you can set how fast this sequence is read (in the screenshot it has a delay of 32 for all voices).

• While being at one of the 3 lower rows (arpeggios)
  • Each time position contains a note played in an arpeggio when you play a note in your keyboard. The arpeggios' notes are relative to the fundamental note you play in the keyboard. The relative notes are counted in semitones, from @ = 0 to L = 12 semitones above the fundamental note. This means that with four @ you'll just heard the note you play and with L = 12 you'll hear that same note one octave higher.
  • @ = 0, A = 1, B = 2, C = 3, D = 4, E = 5, F = 6, G = 7, H = 8, I = 9, J = 10, K = 11, L = 12 semitones.
  • Examples: 1) The sequence @DGJ will play a mayor 7th arpeggio. 2) The sequence @L@L switches between the fundamental note and its octave.
  • You can use arpeggios during the ADS phase and just the plain fundamental note when you release the key. In the example below, voice 1 plays a mayor 7th arpeggio while the note is hold down (green), and the plain note when released (brown); voice 2 plays the plain note while held down and switches between the fundamental note and its octave when released.
  • Keys F1, F2, F3 and F4: selects at which position (1, 2, 3 or 4 in red below) the row's sequence loop is restarted; different values can be set for each voice. For instance, if you enter 2, the arpeggio will be played as: 1, 2, 3, 4 -> 2, 3, 4 -> 2, 3, 4, etc. [verificar que esto funciona así, y puede dar conflictos con la siguiente función]. With the B key in the main menu you can set how fast this sequence is read (in the screenshot below it has a delay of 16 for all voices).
  • Keys 1 To 4: Sets how many notes the arpeggio will have (yellow), always starting from the first note. For instance, if you select 3, the fourth position in the row will be ignored.

Filter settings

With the following keys you can switch on and off which voices routed through the filter and what type of filters you use:

• Keys F2, F4 and F6: sets wheter voice 1, 2 and 3 are filtered (U) or not (@). The first two characters stand for voice 1, the third for voice 2 and the fourth for voice 3.
• Shift + L: turns on/off the low pass filter (on in the example below).
• Shift + H: turns on/off the high pass filter (off in the example).
• Shift + B: turns on/off the band pass filter (off in the example).

WIn the example below, the low pass filtered is selected, voices 1 (U) and 2 (U) are routed through the filter while voice 3 (@) is bypassed.

Troubleshooting

The most frequent problem I had were notes that didn't stop to sound when I released the key on the piano. And the most common cause behind this problem were low batteries in the MIDI controller. It's advisible to use a power supply or make sure that batteries are fully loaded.

Check that all wires and parts are properly soldered or inserted in the breadboard.

To pin down some problems you can check the board as explained before. Any time you press a key, the Arduino built in LED should briefly blink, and the same should happen when you release the key. If this is not the case, something went wrong with the sketch upload or some parts aren't properly connected in the circuit. If the LED blinks but the C64 doesn't produce any sound, then the problem lies somewhere between Arduino and the C64.