APU period table: Difference between revisions

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(moved the program below the output because most people are looking for something to CNP; added link to Celius' tables with more explanation)
(relationship to piano)
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== Lookup table ==
== Lookup table ==
Here's a lookup table from note numbers (low A = 0) to the values to write to the pulse and triangle period registers.
Here's a lookup table from note numbers to the values to write to the pulse and triangle period registers.
Triangle notes will sound one octave lower.
For the triangle channel, the first value corresponds to the lowest key on a standard piano (an A).
The pulse waves sound one octave higher.
<pre>
<pre>
; NTSC period table generated by mktables.py
; NTSC period table generated by mktables.py
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== Table generator ==
== Table generator ==
This Python program generated the above lookup table.
This Python program generated the above lookup table.
You can use it to make a table for PAL, or you can adjust it for other [[wikipedia:musical tuning]] systems:
You can use it to make a table for PAL, or you can adjust it for other [[wikipedia:musical tuning|musical tuning]] systems:
<pre>
<pre>
#!/usr/bin/env python
#!/usr/bin/env python

Revision as of 23:45, 3 April 2010

APU Pulse and APU Triangle use "period" values to set the pitch of the note. But some people might not know the piano key frequencies or how to convert them to periods for the NES. Fortunately, this has been done for you.

Lookup table

Here's a lookup table from note numbers to the values to write to the pulse and triangle period registers. For the triangle channel, the first value corresponds to the lowest key on a standard piano (an A). The pulse waves sound one octave higher.

; NTSC period table generated by mktables.py
.export periodTableLo, periodTableHi
.segment "RODATA"
periodTableLo:
  .byt $f1,$7f,$13,$ad,$4d,$f3,$9d,$4c,$00,$b8,$74,$34
  .byt $f8,$bf,$89,$56,$26,$f9,$ce,$a6,$80,$5c,$3a,$1a
  .byt $fb,$df,$c4,$ab,$93,$7c,$67,$52,$3f,$2d,$1c,$0c
  .byt $fd,$ef,$e1,$d5,$c9,$bd,$b3,$a9,$9f,$96,$8e,$86
  .byt $7e,$77,$70,$6a,$64,$5e,$59,$54,$4f,$4b,$46,$42
  .byt $3f,$3b,$38,$34,$31,$2f,$2c,$29,$27,$25,$23,$21
  .byt $1f,$1d,$1b,$1a,$18,$17,$15,$14
periodTableHi:
  .byt $07,$07,$07,$06,$06,$05,$05,$05,$05,$04,$04,$04
  .byt $03,$03,$03,$03,$03,$02,$02,$02,$02,$02,$02,$02
  .byt $01,$01,$01,$01,$01,$01,$01,$01,$01,$01,$01,$01
  .byt $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
  .byt $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
  .byt $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
  .byt $00,$00,$00,$00,$00,$00,$00,$00

Table generator

This Python program generated the above lookup table. You can use it to make a table for PAL, or you can adjust it for other musical tuning systems:

#!/usr/bin/env python
#
# Lookup table generator for note periods
# Copyright 2010 Damian Yerrick
#
# Copying and distribution of this file, with or without
# modification, are permitted in any medium without royalty
# provided the copyright notice and this notice are preserved.
# This file is offered as-is, without any warranty.
#
from __future__ import with_statement, division
import sys

ntscOctaveBase = 39375000.0/(22 * 16 * 55)
palOctaveBase = 266017125.0/(10 * 16 * 16 * 55)
maxNote = 80

def makePeriodTable(filename, pal=False):
    semitone = 2.0**(1./12)
    octaveBase = palOctaveBase if pal else ntscOctaveBase
    relFreqs = [(1 << (i // 12)) * semitone**(i % 12)
                for i in xrange(maxNote)]
    periods = [int(round(octaveBase / freq)) - 1 for freq in relFreqs]
    systemName = "PAL" if pal else "NTSC"
    with open(filename, 'wt') as outfp:
        outfp.write("""; %s period table generated by mktables.py
.export periodTableLo, periodTableHi
.segment "RODATA"
periodTableLo:\n"""
                    % systemName)
        for i in range(0, maxNote, 12):
            outfp.write('  .byt '
                        + ','.join('$%02x' % (i % 256)
                                   for i in periods[i:i + 12])
                        + '\n')
        outfp.write('periodTableHi:\n')
        for i in range(0, maxNote, 12):
            outfp.write('  .byt '
                        + ','.join('$%02x' % (i >> 8)
                                   for i in periods[i:i + 12])
                        + '\n')

def makePALPeriodTable(filename):
    return makePeriodTable(filename, pal=True)

tableNames = {
    'period': makePeriodTable,
    'palperiod': makePALPeriodTable
}

def main(argv):
    if len(argv) >= 2 and argv[1] in ('/?', '-?', '-h', '--help'):
        print "usage: %s TABLENAME FILENAME" % argv[0]
        print "known tables:", ' '.join(sorted(tableNames))
    elif len(argv) < 3:
        print "mktables: too few arguments; try %s --help" % argv[0]
    elif argv[1] in tableNames:
        tableNames[argv[1]](argv[2])
    else:
        print "mktables: no such table %s; try %s --help" % (argv[1], argv[0])

if __name__=='__main__':
    main(sys.argv)

See also