Subject:
freq_to_fnum adlib
From:
"Leonard, James R \(Jim\)" <jleonard@alcatel-lucent.com>
Date:
Mon, 21 Apr 2008 14:49:18 -0500
To:
"Jim Leonard" <trixter@oldskool.org>

compare this to demo.pas

Copyright (C) by Hannu Savolainen 1993-1997

static void freq_to_fnum    (int freq, int *block, int *fnum)
{
        int f, octave;

        /*
         * Converts the note frequency to block and fnum values for the FM chip
         */
        /*
         * First try to compute the block -value (octave) where the note belongs
         */

        f = freq;

        octave = 5;

        if (f == 0)
                octave = 0;
        else if (f < 261)
        {
                while (f < 261)
                {
                        octave--;
                        f <<= 1;
                }
        }
        else if (f > 493)
        {
                while (f > 493)
                {
                         octave++;
                         f >>= 1;
                }
        }

        if (octave > 7)
                octave = 7;

        *fnum = freq * (1 << (20 - octave)) / 49716;
        *block = octave;
}

-- 
Jim Leonard, Unix SA, Alcatel-Lucent