TI-99/4A BASIC: A Program for Microtonal Adjustment

[ColecoFan1981]

Hi,

 

For those of you familiar with the Texas Instruments TI-99/4A and its BASIC program, what is the right way to write a program on it about microtonal adjustment? I want to use the FOR-NEXT and IF-THEN statements in the program; however, I do not know where to put them in regards to the mathematics below.

 

It could start off as something like this:

5 CALL CLEAR

10 LET F=60

20 LET Y=1200*LOG(F/16.3515978312876)/LOG(2)

 

About microtonal adjustments relating to musical pitches:

0 = C; 1 = C#; 2 = D; 3 = D#; 4 = E; 5 = F; 6 = F#; 7 = G; 8 = G#; 9 = A; 10 = A#; 11 = B

 

C1 = 32.7 Hz

C#1 = 34.65 Hz

D1 = 36.71 Hz

D#1 = 38.89 Hz

E1 = 41.2 Hz

F1 = 43.65 Hz

F#1 = 46.25 Hz

G1 = 49 Hz

G#1 = 51.91 Hz

A1 = 55 Hz

A#1 = 58.27 Hz

B1 = 61.74 Hz

 

To find out what note corresponds to a frequency of 52.5 Hz:

Y=1200*LOG(52.5/16.3515978312876)/LOG(2)

Y=2019.46

 

To find out octave N; it is the integer part of Y/1200 = 2019.46/1200 = 1

Then subtract 1*1200 from 2019.46, which gives Y'=819.46

 

Semitone (S) = integer part of 819.46/100 = 8. The note to insert is a G# (7=G; 8=G#; 9=A).

Now subtract 100*8 from 819.46. The result is 19.46, rounded to M=19 cents.

We have to insert a G#, 1st octave, with a microtonal adjustment of 19 cents.

Same frequency can be obtained by using an A, 1st octave, with a microtonal adjustment of (19-100) = -81 cents.

 

Thank you in advance,

 

 

 

Ben

Edited April 12, 2010 by ColecoFan1981