A simple-to-use sound file writer
in [Python]
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From: Alf P. Steinbach on 17 Jan 2010 09:16 * Alf P. Steinbach: > * Steve Holden: >> Alf P. Steinbach wrote: >>> * Steve Holden: >>>> Alf P. Steinbach wrote: >>>>> * Grant Edwards: >>>>>> On 2010-01-15, Steve Holden <steve(a)holdenweb.com> wrote: >>>>>> >>>>>>> I will, however, observe that your definition of a square wave is >>>>>>> what I >>>>>>> would have to call a "'square' wave" (and would prefer to call a >>>>>>> "pulse >>>>>>> train"), as I envisage a square wave as a waveform having a 50% duty >>>>>>> cycle, as in >>>>>>> >>>>>>> ___ ___ >>>>>>> | | | | >>>>>>> | | | | >>>>>>> | | | | >>>>>>> +---+---+---+---+ and so on ad infinitum, (though I might allow you >>>>>>> | | | | to adjust the position >>>>>>> | | | | of y=0 if you want) >>>>>>> |___| |___| >>>>>> That is a square wave. >>>>>> >>>>>>> as opposed to your >>>>>>> >>>>>>> _ >>>>>>> | | >>>>>>> | | >>>>>>> ______| |______ ______ >>>>>>> | | >>>>>>> | | >>>>>>> |_| >>>>>> That isn't. >>>>>> >>>>>> Arguing to the contrary is just being Humpty Dumpty... >>>>> Neither I nor Steve has called that latter wave a square wave. >>>>> >>>>> Steve, quoted above, has written that I defined a square wave that >>>>> way. >>>>> I have not. So Steve's statement is a misrepresentation (I >>>>> described it >>>>> as a sum of two square waves, which it is), whatever the reason for >>>>> that >>>>> misrepresentation. >>>>> >>>>> >> > [snip] >> So here you have an interesting example of a >> piece of code that is pathological in Python2. All you have to change is >> to add >> >> from __future__ import __division__ >> >> and bingo! It's a multi-language program. But try seeing what 2to3 says >> about your Python3 code :) >> >> I will forgive you the omission of the ".0" because I too would assume >> that it would be slower. > > I did not make any such assumption, no. The *1 just lingered from some > testing. > > > [snip] >> and so on, but I still get silence from the Quicktime player. > > I don't know, sorry. > > It might be that [simple_sound] also needs the "from __future__" treatment. > > But anyway, with 2.x compatible code you can now see that the sample > values produced are correct (just print them, or graph them). I have now installed CPython 2.6.4 and the code presented upthread (the one with divisions fixed for 2.x compatibility) worked nicely with CPython 2.6.4, even though with a deprecation warning. It produced the exact same sound file (bytes) as with CPython 3.1.1. And the QuickTime 7.3 player played it with no problem, a base A pure sinewave, composed utterly of 50% duty cycle square waves, resounding in my headphones -- it also works with WinAmp 5.54, Windows Mediaplayer 10.00 and VLC 0.9.9, i.e. I'm unable to reproduce the problem. So I suspect that you may lack a suitable codec, or it might be a PEBKAC problem? Cheers & hth., - Alf PS: I had expected some jaggies and such since I only divided the cycle into 100 intervals, but graphing the data in Excel it showed a perfect sine. :-)
From: Alf P. Steinbach on 17 Jan 2010 10:14 * Alf P. Steinbach: > Just as a contribution, ... The original code I posted was only written for Python 3.1.1 (because the code was for my writings which assumes 3.x). In the simple_sound module this caused a deprecation warning with 2.x. And the example program didn't work with 2.x. I've now installed CPython 2.6.4 and fixed the code so that it works nicely also with that version of Python. <code file="simple_sound.py"> "Generate simple mono (single-channel) [.wav], [.aiff] or [.aifc] files." # Works with Python 2.6.4 and Python 3.1.1, but has not been extensively tested. # Author: Alf P. Steinbach. # # Changes from original 3.1.1 version: # * A deprecation warning suppressed by explicit cast to int. # * The default sound library is now not imported until it's actually used. # * Added exception handling (for the code's original purpose I couldn't). # # Notes: # (1) It might be possible to optimize this by using array of 16-bit integers, then # checking 'sys.byteorder' and doing a 'data.byteswap()' call as appropriate. # (2) Data is kept in memory until 'close' due to a bug in the 'wave' module. That bug # has now been fixed. But it may be present in any Python installation. import collections import array import math default_sample_rate = 44100 # Usual CD quality. def sample_sawtooth( freq, t ): linear = freq*t % 1.0 return 2*linear - 1.0 def sample_square( freq, t ): linear = freq*t % 1.0 if linear < 0.5: return -1.0 else: return 1.0 def sample_triangle( freq, t ): linear = freq*t % 1.0 if linear < 0.5: return 4.0*linear - 1.0 else: return 3.0 - 4.0*linear def sample_sine( freq, t ): return math.sin( 2*math.pi*freq*t ) DataFormat = collections.namedtuple( "DataFormat", "open_func, append_int16_func" ) def _append_as_big_endian_int16_to( bytes_array, i ): if i < 0: i = i + 65536 assert( 0 <= i < 65536 ) bytes_array.append( i // 256 ) bytes_array.append( i % 256 ) def _append_as_little_endian_int16_to( bytes_array, i ): if i < 0: i = i + 65536 assert( 0 <= i < 65536 ) bytes_array.append( i % 256 ) bytes_array.append( i // 256 ) def aiff_format(): import aifc return DataFormat( aifc.open, _append_as_big_endian_int16_to ) def wav_format(): import wave return DataFormat( wave.open, _append_as_little_endian_int16_to ) class Writer: "Writes normalized samples to a specified file or file-like object" def __init__( self, filename, sample_rate = default_sample_rate, data_format = None ): if data_format is None: data_format = aiff_format() self._sample_rate = sample_rate self._append_int16_func = data_format.append_int16_func self._writer = data_format.open_func( filename, "w" ) self._writer.setnchannels( 1 ) self._writer.setsampwidth( 2 ) # 2 bytes = 16 bits self._writer.setframerate( sample_rate ) self._samples = [] def sample_rate( self ): return self._sample_rate def write( self, normalized_sample ): assert( -1 <= normalized_sample <= +1 ) self._samples.append( normalized_sample ) def close( self ): try: data = array.array( "B" ) # B -> unsigned bytes. append_int16_to = self._append_int16_func for sample in self._samples: level = int( round( 32767*sample ) ) append_int16_to( data, level ) self._writer.setnframes( len( self._samples ) ) self._writer.writeframes( data ) finally: self._writer.close() def example( filename = "ringtone.aiff" ): global default_sample_rate sample_rate = default_sample_rate total_time = 2 n_samples = sample_rate*total_time writer = Writer( filename ) for i in range( n_samples ): t = 1.0*i/sample_rate samples = ( sample_sine( 440, t ), sample_sine( (5.0/4.0)*440, t ), ) sample = sum( samples )/len( samples ) writer.write( sample ) writer.close() if __name__ == "__main__": example() </code> Cheers, & enjoy!, - Alf
From: TimmyGee on 17 Jan 2010 19:54 On Jan 15, 3:43 pm, Steve Holden <st...(a)holdenweb.com> wrote: > Alf P. Steinbach wrote: > > [...]> Perhaps you'd also admit to being wrong, and retract your innuoendo etc.? > > Disregarding any matters of right or wrong (for this post, at least), I > herebe retract anything I have said about you that you consider > innuendo. Feel free to remind me what that was. > > regards > Steve > -- > Steve Holden +1 571 484 6266 +1 800 494 3119 > PyCon is coming! Atlanta, Feb 2010 http://us.pycon.org/ > Holden Web LLC http://www.holdenweb.com/ > UPCOMING EVENTS: http://holdenweb.eventbrite.com/ Now now children...
From: Albert van der Horst on 25 Jan 2010 09:50
In article <hinfjn$8s9$1(a)speranza.aioe.org>, Mel <mwilson(a)the-wire.com> wrote: >Alf P. Steinbach wrote: >> * Steve Holden: > >>> It's not clear to me that you can approximate any waveform with a >>> suitable combination of square waves, >> >> Oh. It's simple to prove. At least conceptually! :-) >> >> Consider first that you need an infinite number of sine waves to create a >> perfect square wave. >> >> The opposite also holds: infinite number of square waves to create a >> perfect sine wave (in a way sines and squares are opposites, the most >> incompatible). > >No, it doesn't. The infinite set of sine waves that make a square wave >leave out the sine waves of frequency 2f, 4f, 6f, 8f, ... (2*n*f) ... . >Once you've left them out, you can never get them back. So sawtooth waves, >for example, can't generally be built out of sets of square waves. Bullshit. My Boehm (B\"ohm) electronic organ does exactly that. They even have a chip for it. In the 70's it was a great hype, a sawtooth organ. Well not exactly a hype, the sound, especially the low registers, is dramatically better. If you're interested in frequencies above audible (organ builders aren't), you need an infinity of squares to build a perfect sawtooth. But then you need an inifinity of sines to build a perfect square wave. <SNIP> > Mel. Groetjes Albert -- -- Albert van der Horst, UTRECHT,THE NETHERLANDS Economic growth -- being exponential -- ultimately falters. albert(a)spe&ar&c.xs4all.nl &=n http://home.hccnet.nl/a.w.m.van.der.horst |