Music Thing Modular / Chord Organ DIY
04 mars 2017 - Aucun commentaire
Chord organ is very simple.
Chord = choose the chord shape; minor, major, seventh etc. Shapes can be defined by editing a text file on the SD Card (see below). Chords can have up to 8 notes.
Root = choose the root note, in semitones from C-2 to C+2
Waveform = push to select one of four waveforms: Sine, Square, Sawtooth and weird-gnarly-pulse-an-octave-below.
Chord + Root CV inputs. The Root CV input is NOT volt/octave, but the output notes are perfectly in standard tuning (A = 440hz).
Trig = Trigger output, which pulses every time the chord changes
Out = Audio output
Editing the SD Card
Chord Organ needs an SD card (any size) to function — you can use the SD card from a Radio Music. It creates a tiny text file called CHORDORG.TXT in the root of the SD card, which can be edited to change the chords.
When you open the file it looks like this.
2 [0,3,7,12,0] Minor
3 [0,4,7,11,0] Major 7th
4 [0,3,7,10,0] Minor 7th
5 [0,4,7,11,14] Major 9th
6 [0,3,7,10,14] Minor 9th
7 [0,5,7,12,0] Suspended 4th
8 [0,7,12,0,7] Power 5th
9 [0,5,12,0,5] Power 4th
10 [0,4,7,8,0] Major 6th
11 [0,3,7,8,0] Minor 6th
12 [0,3,6,0,3] Diminished
13 [0,4,8,0,4] Augmented
14 [0,0,0,0,0] Root
15 [-12,-12,0,0,0] Sub Octave
16 [-12,0,0,12,24] 2 up 1 down octaves
Each chord is described in numbers. 0 is the root. 12 is the octave above. -12 is the octave below. The text outside the square brackets is ignored, so the ‘Major 7th’ text is just there as a reminder.
The Wikipedia List of Chords page has 70+ chord shapes. The column marked “p.c. #s” shows the numbers you need here, in Integer Notation, (with “10” and “11” replaced by “t” and “e”). For example, the Dominant Ninth is listed as 0 4 7 t 2, which you should enter as 0 4 7 10 2. You probably want to raise the last 2 up an octave, so it becomes 0 4 7 10 14.
If you have different numbers of notes in each chord, you may get clicks as you switch between them; you can experiment to see if you mind.
links
https://www.muffwiggler.com/forum/viewtopic.php?t=177939&highlight=
build : https://github.com/TomWhitwell/RadioMusic/wiki/Preparing-the-Teensy
https://github.com/TomWhitwell/Chord-Organ