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I am using scipy.io.wavfile to read a WAV file and playing it with pyaudio. Before the numpy array is written to a string and output through pyaudio, I would like to be able to apply some sort of function (sin, cos, etc.) to the 16-bit numpy array.

Does anyone have any experience doing something like this? Should I convert to float, apply the function to the float data, then convert back? I am also aware of fixed point arithmetic, but not sure if I can apply it here.

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  • $\begingroup$ It depends on what kind of processing you want to apply (I assume it is not any prototyping of algorithms for a DSP chip). Generally it's OK to convert your samples to floats and process everything using them. If you want to save the filtered samples back to int16, then just set the appropriate dtype of your array and don't worry about conversion. On the other hand if you want to play back the result using pyaudio then simply set the stream to be a float. pyaudio + *numpy*/*scipy is a very good choice. $\endgroup$ – jojek♦ May 26 '15 at 8:57
  • $\begingroup$ "I would like to be able to apply some sort of function (sin, cos, etc.) to the 16-bit numpy array." You want to distort it? $\endgroup$ – endolith Jul 25 '15 at 4:31
  • $\begingroup$ Yeah, but in a specific way. $\endgroup$ – soultrane Jul 25 '15 at 13:12
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If you're doing ANY audio signal processing in python, I heartily recommend librosa. Your scipy route will work (read as float, process, playback), but it is less direct. Also, I recommend sticking with float, as fixed-point work is more relevant if your code is running on an embedded/mobile system sans-FPU.

You can pip install librosa and get applying math functions quickly. Check out the introduction ipython notebook. Additionally, if you're doing more serious work, there is great integration with scikit-learn machine learning pipelines.

To get you started your code might look like this:

import librosa
import numpy as np

# Load the example track
y, sr = librosa.load("myfile.wav")

# apply mathematical functions or processes to 'y' here:

# If you do this in an ipython notebook (highly recommended as a interactive python env), 
# you can play back in one line!
IPython.display.Audio(data=y, rate=sr)
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  • $\begingroup$ Thanks for the response. One thing I am confused about: it looks like you are using librosa to play the audio, but I am using pyaudio to play...so librosa would replace both? And does this method of audio playback also depend on using IPython notebook? $\endgroup$ – soultrane May 26 '15 at 16:03
  • $\begingroup$ NO! I'm only using librosa to load the wav file! Once the data is loaded in y you can use anything for playback. In my example, since I use iPython, I showed how you can playback. But you can use anything, pyaudio, pydub, etc. It is just a vector of floats afterall. I thought iPython is easier than this: stackoverflow.com/questions/6951046/pyaudio-help-play-a-file. Hope that helps! $\endgroup$ – ruoho ruotsi May 26 '15 at 22:16

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