December 02, 2012

BP on the Roland HandSonic HPD-15

The Roland HandSonic HPD-15 hand drum includes some tuned percussion instruments. You can edit the pitch of each pad in cents.  The pads are grouped into 3 sets of 5, as shown:

You can edit the pitch of each pad individually, and further adjust the pitch of an entire set (A, B or C).  The pad set adjustment is very helpful when creating a patch for any HPD-15 instrument that is voiced for a higher or lower octave.

After several experiments, I finally settled on this arrangement of the Bohlen-Pierce scale notes.  It is fully chromatic from D to D'.  I didn't include a low Db as it seemed less important than the high D' for modal music. 
I tuned the notes to the C Lambda scale in just intonation with A=440 Hz (pad A2).  The first song recorded with this system was Fuse Blue.  The HPD-15 is somewhat buried in the final mix. I've created a separate MP3 file of just the HandSonic tracks so that you can hear what it sounds like: FuseBlueHandSonic.mp3.

I'm happy to answer any technical questions from other HandSonic players who are into BP or other alternate scales.  The HPD-15 isn't a real sensitive instrument, but its fine tuning capabilities make it a very useful tool for creating a variety of sounds in real time performance.

October 26, 2012

7-Limit Harmonies in the Bohlen Pierce Scale

The most consonant harmonies in the Bohlen Pierce scale (to my ear) are those that fall within the gamut of Harry Partch's 7-limit just intonation system. The BP intervals 9/7 and 7/5 (steps 3 and 4) seem to be the most pleasing, and their equal temperament counterparts are less than 4 cents from just.

The step 2 interval 25/21 is 302 cents, an acceptable minor third to western ears, but equal temperament changes it to a flat-sounding 292 cents.

The step 12 interval 25/9 (B note) is totally outside of the western 12-tone system.

This chart shows the intersection between the Bohlen Pierce scale and the 7-limit just intonation system.  The D and B notes (in blue) suffer the problems mentioned above.  The difference between cents and round hundreds is a rough indicator of how alien the interval will sound compared to traditional western harmony.

steps name ratio cents cents ET 12-tone name
0 C 1/1 0 0 Unison
2 D 25/21 302 293 Minor 3rd
3 E 9/7 439 435 Dim 4th
4 F 7/5 582 585 Tritone
6 G 5/3 884 877 Major 6th
7 H 9/5 1018 1024 Minor 7th
9 J 15/7 1319 1316 Dim 9th
10 A 7/3 1467 1463 Aug 9th
12 B 25/9 1769 1755 none
13 C 3/1 1902 1902 12th