A simple-to-use sound file writer
Alf P. Steinbach
alfps at start.no
Sat Jan 16 14:33:20 CET 2010
* Alf P. Steinbach:
> * Steve Holden:
>>>
>> Though for what it's worth I wasn't impressed by the results of running
>> the posted program, since it yielded an AIFF file of mostly zeroes that
>> produced no audible sound.
>>
>> $ od -bc sinewave.aiff
>> 0000000 106 117 122 115 000 002 261 076 101 111 106 106 103 117 115 115
>> F O R M \0 002 261 > A I F F C O M M
>> 0000020 000 000 000 022 000 001 000 001 130 210 000 020 100 016 254 104
>> \0 \0 \0 022 \0 001 \0 001 X 210 \0 020 @ 016 254 D
>> 0000040 000 000 000 000 000 000 123 123 116 104 000 002 261 030 000 000
>> \0 \0 \0 \0 \0 \0 S S N D \0 002 261 030 \0 \0
>> 0000060 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000
>> \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 \0
>> *
>> 0530500 000 000 000 000 000 000
>> \0 \0 \0 \0 \0 \0
>> 0530506
>>
>> Any idea what I did wrong?
>
[snip]
> Hm, I'm inclined to think that you used Python 2.x instead of my 3.1.1!
>
> I no longer have Python 2.x installed, I think, so no time to test that
> now.
>
> But would that be the case?
>
> If so, perhaps changing "t = 1*i/sample_rate" to "t =
> (1.0*i)/sample_rate" will help?
I fixed up two more divisions. Not sure if this is 2.x-compatible, but perhaps:
<code>
# Python 3.1.1 -- *probably* works also with 2.x?
# Generating a sine wave as a sum of square waves of various amplitudes & phases.
import simple_sound
# Step 1 "Divide a full cycle of the sine wave into n intervals."
n = 100
# Step 2 -- Just an explanation of the rest
# Step 3 "In the first half of the cycle, for each bar create that bar as
# a square wave of frequency f, amplitude half the bar's height, and phase
# starting at the bar's left, plus same square wave with negative sign
# (inverted amplitude) and phase starting at the bar's right."
square_waves = []
for i in range( n//2 ):
middle_of_interval = (i + 0.5)/n
amp = simple_sound.sample_sine( 1, middle_of_interval ) / 2.0
def first_square_wave( t, i = i, amp = amp ):
phase = 1.0*i/n
return amp*simple_sound.sample_square( 1.0, t - phase )
def second_square_wave( t, i = i, amp = amp ):
phase = 1.0*(i + 1)/n
return -amp*simple_sound.sample_square( 1.0, t - phase )
square_waves.append( first_square_wave )
square_waves.append( second_square_wave )
# Step 4 "Sum all the square waves from step 3."
def sample_squares( f, t ):
samples = []
o_time = f*t
for func in square_waves:
sq_sample = func( o_time )
samples.append( sq_sample )
return sum( samples )
# Finally, generate this is in an [.aiff] file:
if True:
f = 440
sample_rate = 44100
total_time = 2
n_samples = sample_rate*total_time
writer = simple_sound.Writer( "sinewave.aiff" )
for i in range( n_samples ):
t = 1.0*i/sample_rate
sample = sample_squares( f, t )
writer.write( sample )
writer.close()
</code>
Cheers & hth.,
- Alf
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