28 Feb
2015
28 Feb
'15
11:36 a.m.
On Fri, Feb 27, 2015 at 09:24:50AM -0500, tom haddington wrote:
Hey, Everybody--
Saluton
i loaded bristol with a scala (.scl) file, this
morning. That much worked
fine. However, both my midi keyboard and the gui keyboard are nowhere near
middle C. i've even tuned my midi keyboard up (a maximum) three octaves,
and my middle C is still two octaves too low. Can this be prevented or
adjusted in anyway?
The bad news is that Bristol uses only 440 Hz, 69 and 0 for reference
frequency, keynum and scale degree-index respectively. For example,
with the pitch values of a just intonation:
16/15 9/8 6/5 5/4 4/3 7/5 3/2 8/5 5/3 9/5 15/8 2/1
the notes are:
A (1) A# (16/15) B (9/8) C (6/5) C# (5/4) D (4/3)
D# (7/5) E (3/2) F (8/5) F# (5/3) G (9/5) G# (15/8)
The middle C (keynum 60) is
440 x 3/5 = 264 Hz
and probably it is not a big problem for you.
But what is the frequency related to the keynum 60 when the number of
the notes of a scale is not 12, and/or the interval between keynum 69
and keynum 72 is not a 3min ? I think it is your problem with Bristol.
For example, the pitch values of a golden pentatonic are
5/4 21/16 3/2 13/8 2/1
and the keymap starting from keynum 60 (middle C) is
60 5/16
61 21/64
62 3/8
63 13/32
64 1/2
65 5/8
66 21/32
67 3/4
68 13/16
69 1
70 5/4
71 21/16
72 3/2
73 13/8
74 2
If we press the key of the middle C, we hear the frequency
440 * 5/16 = 137.5 Hz
and obviously it is not a middle C.
Without the possibility to define a keymap, the trick is to add other
notes to get a (not necessarily chromatic) scale with 12 notes. One
of the possible scales from the previous pentatonic is
16/15 9/8 6/5 5/4 21/16 7/5 3/2 13/8 5/3 9/5 15/8 2/1
But what if we want play the ji-scale of the first example starting
from another note ? The trick is to write a scl file with the intervals
of a modal chromatic scale. If we want a ji in C, we write a modal
chromatic scale in A by translating the pitch values:
9/5 / 5/3 = 27/25
15/8 / 5/3 = 9/8
2/1 / 5/3 = 6/5
32/15 / 5/3 = 32/25
[...]
and the result is
27/25 9/8 6/5 32/25 27/20 36/25 3/2 8/5 42/25 9/5 48/25 2/1
In this example, the interval of a minor third is always 6/5, therefore
the frequency related to the middle C remains 264 Hz. Now we can play
the follow notes with Bristol:
C (1) C# (16/15) D (9/8) D# (6/5) E (5/4) F (4/3)
F# (7/5) G (3/2) G# (8/5) A (5/3) A# (9/5) B (15/8)
Just my 1200 cents :-)
Tito
P.S. I have written some utilities to create and manage musical tunings:
http://incudine.sourceforge.net/tutorial_tuning.html