bicycle-bell/audio/bell.py

72 lines
2.5 KiB
Python

#!/usr/bin/python
# Bicycle Bell/Horn firmware
# Copyright (C) 2015 Stuart Longland
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
import math
import wave
import struct
import textwrap
# Generate a bell sound
F_sample = 6400 # 6.4kHz sample rate
F_bell = 2063 # Fundamental frequency
F_bell_mod = 15.625 # Modulated amplitude
F_reverb = 3.77 # Reverberation frequency
A_reverb = 0.07 # Reverberation amplitude
duration = 1.0 # Duration
decay = 1.0 # Decay
samples = []
bell = lambda t : ((1.0+math.cos(math.pi*t/duration))/2) * \
(decay ** t) * \
(1.0 - (A_reverb * math.cos(2*math.pi*F_reverb*t)) - (A_reverb/2)) * \
(math.cos(2*math.pi*F_bell*t) * \
math.sin(2*math.pi*F_bell_mod*t))
for n in range(0, int(duration*F_sample)):
t = float(n)/float(F_sample)
samples.append(int(127*bell(t)) + 127)
assert samples[-1] >= 0, '%s <= 0' % samples[-1]
assert samples[-1] <= 255, '%s > 255' % samples[-1]
num_samples = len(samples)
# C output
with file('bellsnd.c','w') as f:
f.write('#include "bellsnd.h"\n')
f.write('const uint8_t bell[%s] PROGMEM = {\n' % num_samples)
f.write('\n'.join(textwrap.wrap(', '.join([str(s) for s in samples]),
initial_indent='\t', subsequent_indent='\t',
expand_tabs=False)))
f.write('\n};\n')
with file('bellsnd.h','w') as f:
f.write('#include <stdint.h>\n')
f.write('#include <avr/pgmspace.h>\n')
f.write('#define BELL_RATE (%s)\n' % F_sample)
f.write('#define BELL_SZ (%s)\n' % num_samples)
f.write('const uint8_t bell[%s] PROGMEM;\n' % num_samples)
# For the sake of analysis, we'll dump wav audio too
f = wave.open('bellsnd.wav','w')
f.setnchannels(1)
f.setsampwidth(1)
f.setframerate(F_sample)
f.setnframes(num_samples)
f.setcomptype('NONE','not compressed')
f.writeframes(''.join([
struct.pack('B', s) for s in samples
]))
f.close()