Reading wav files in Python

Question

I need to analyze sound written in a  wav file  For that I need to transform this file into set of numbers  arrays  for example   I think I need to use the wave package  However  I do not know how exactly it works  For example I did the following   import wave w   wave open   usr share sounds ekiga voicemail wav    r   for i in range w getnframes         frame   w readframes i      print frame   As a result of this code I expected to see sound pressure as function of time  In contrast I see a lot of strange  mysterious symbols  which are not hexadecimal numbers   Can anybody  pleas  help me with that

User · Answer

You can accomplish this using the scikits.audiolab module. It requires NumPy and SciPy to function, and also libsndfile.

Note, I was only able to get it to work on Ubunutu and not on OSX.

from scikits.audiolab import wavread

filename = "testfile.wav"

data, sample_frequency,encoding = wavread(filename)

Now you have the wav data

User · Answer

Different Python modules to read wav  There is at least these following libraries to read wave audio files   SoundFile scipy io wavfile  from scipy  wave  to read streams  Included in Python 2 and 3  scikits audiolab  unmaintained since 2010  sounddevice  play and record sounds  good for streams and real-time  pyglet librosa  music and audio analysis  madmom  strong focus on music information retrieval  MIR  tasks   The most simple example  This is a simple example with SoundFile  import soundfile as sf data  samplerate   sf read  existing file wav      Format of the output  Warning  the data are not always in the same format  that depends on the library  For instance  from scikits import audiolab from scipy io import wavfile from sys import argv for filepath in argv 1        x  fs  nb bits   audiolab wavread filepath      print  Reading with scikits audiolab wavread    x      fs  x   wavfile read filepath      print  Reading with scipy io wavfile read    x   Output  Reading with scikits audiolab wavread    0           0           0               -0 00097656 -0 00079346 -0 00097656  Reading with scipy io wavfile read     0   0   0      -32 -26 -32   SoundFile and Audiolab return floats between -1 and 1  as matab does  that is the convention for audio signals   Scipy and wave return integers  which you can convert to floats according to the number of bits of encoding  for example  from scipy io wavfile import read as wavread samplerate  x   wavread audiofilename     x is a numpy array of integers  representing the samples    scale to -1 0 -- 1 0 if x dtype     int16       nb bits   16    - gt  16-bit wav files elif x dtype     int32       nb bits   32    - gt  32-bit wav files max nb bit   float 2     nb bits - 1   samples   x    max nb bit   1     samples is a numpy array of floats representing the samples

User · Answer

PyDub  http   pydub com   has not been mentioned and that should be fixed  IMO this is the most comprehensive library for reading audio files in Python right now  although not without its faults  Reading a wav file   from pydub import AudioSegment  audio file   AudioSegment from wav  path to wav     or audio file   AudioSegment from file  path to wav      do whatever you want with the audio  change bitrate  export  convert  read info  etc    Check out the API docs http   pydub com    PS  The example is about reading a wav file  but PyDub can handle a lot of various formats out of the box  The caveat is that it s based on both native Python wav support and ffmpeg  so you have to have ffmpeg installed and a lot of the pydub capabilities rely on the ffmpeg version  Usually if ffmpeg can do it  so can pydub  which is quite powerful    Non-disclaimer  I m not related to the project  but I am a heavy user

User · Answer

If you want to procces an audio block by block  some of the given solutions are quite awful in the sense that they imply loading the whole audio into memory producing many cache misses and slowing down your program  python-wavefile provides some pythonic constructs to do NumPy block-by-block processing using efficient and transparent block management by means of generators  Other pythonic niceties are context manager for files   metadata as properties    and if you want the whole file interface  because you are developing a quick prototype and you don t care about efficency  the whole file interface is still there   A simple example of processing would be   import sys from wavefile import WaveReader  WaveWriter  with WaveReader sys argv 1   as r       with WaveWriter               output wav               channels r channels              samplerate r samplerate                as w              Just to set the metadata         w metadata title   r metadata title     II          w metadata artist   r metadata artist            This is the prodessing loop         for data in r read iter size 512                data 1      8       lower volume on the second channel             w write data    The example reuses the same block to read the whole file  even in the case of the last block that usually is less than the required size  In this case you get an slice of the block  So trust the returned block length instead of using a hardcoded 512 size for any further processing

User · Answer

Here s a Python 3 solution using the built in wave module  1   that works for n channels  and 8 16 24    bits  import sys import wave  def read wav path       with wave open path   quot rb quot   as wav          nchannels  sampwidth  framerate  nframes         wav getparams           print wav getparams     quot  nBits per sample   quot   sampwidth   8           signed   sampwidth  gt  1    8 bit wavs are unsigned         byteorder   sys byteorder    wave module uses sys byteorder for bytes          values         e g  for stereo  values i     left val  right val          for   in range nframes               frame   wav readframes 1     read next frame             channel vals         mono has 1 channel  stereo 2  etc              for channel in range nchannels                   as bytes   frame channel   sampwidth   channel   1    sampwidth                  as int   int from bytes as bytes  byteorder  signed signed                  channel vals append as int              values append channel vals       return values  framerate  You can turn the result into a NumPy array  import numpy as np  data  rate   read wav path  data   np array data   Note  I ve tried to make it readable rather than fast  I found reading all the data at once was almost 2x faster  E g  with wave open path   quot rb quot   as wav      nchannels  sampwidth  framerate  nframes         wav getparams       all bytes   wav readframes -1   framewidth   sampwidth   nchannels frames    all bytes i   framewidth   i   1    framewidth              for i in range nframes    for frame in frames           Although python-soundfile is roughly 2 orders of magnitude faster  hard to approach this speed with pure CPython    1  https   docs python org 3 library wave html

User · Answer

IMHO  the easiest way to get audio data from a sound file into a NumPy array is SoundFile  import soundfile as sf data  fs   sf read   usr share sounds ekiga voicemail wav    This also supports 24-bit files out of the box  There are many sound file libraries available  I ve written an overview where you can see a few pros and cons  It also features a page explaining how to read a 24-bit wav file with the wave module

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if its just two files and the sample rate is significantly high  you could just interleave them   from scipy io import wavfile rate1 dat1   wavfile read File1  rate2 dat2   wavfile read File2   if len dat2   gt  len dat1   swap shortest     temp   dat2     dat2   dat1     dat1   temp  output   dat1 for i in range len dat2  2   output i 2  dat2 i 2   wavfile write OUTPUT rate dat

User · Answer

I needed to read a 1-channel 24-bit WAV file  The post above by Nak was very useful  However  as mentioned above by basj 24-bit is not straightforward  I finally got it working using the following snippet   from scipy io import wavfile TheFile    example24bit1channelFile wav   fs  x    wavfile read TheFile     convert the loaded data into a 24bit signal  nx   len x  ny   nx 3 4      four 3-byte samples are contained in three int32 words  y   np zeros  ny    dtype np int32       initialise array    build the data left aligned in order to keep the sign bit operational    result will be factor 256 too high  y 0 ny 4      x 0 nx 3   amp  0x000000FF   lt  lt  8          x 0 nx 3   amp  0x0000FF00   lt  lt  8      x 0 nx 3   amp  0x00FF0000   lt  lt  8  y 1 ny 4      x 0 nx 3   amp  0xFF000000   gt  gt  16          x 1 nx 3   amp  0x000000FF   lt  lt  16      x 1 nx 3   amp  0x0000FF00   lt  lt  16  y 2 ny 4      x 1 nx 3   amp  0x00FF0000   gt  gt  8          x 1 nx 3   amp  0xFF000000   gt  gt  8      x 2 nx 3   amp  0x000000FF   lt  lt  24  y 3 ny 4     x 2 nx 3   amp  0x0000FF00         x 2 nx 3   amp  0x00FF0000     x 2 nx 3   amp  0xFF000000   y   y 256     correct for building 24 bit data left aligned in 32bit words   Some additional scaling is required if you need results between -1 and  1  Maybe some of you out there might find this useful

User · Answer

u can also use simple import wavio library u also need have some basic knowledge of the sound

User · Answer

If you re going to perform transfers on the waveform data then perhaps you should use SciPy  specifically scipy io wavfile

User · Answer

Per the documentation  scipy io wavfile read somefile  returns a tuple of two items  the first is the sampling rate in samples per second  the second is a numpy array with all the data read from the file  from scipy io import wavfile samplerate  data   wavfile read    output audio wav

User · Answer

Using the struct module  you can take the wave frames  which are in 2 s complementary binary between -32768 and 32767  i e  0x8000 and 0x7FFF   This reads a MONO  16-BIT  WAVE file  I found this webpage quite useful in formulating this  import wave  struct  wavefile   wave open  sine wav    r    length   wavefile getnframes   for i in range 0  length       wavedata   wavefile readframes 1      data   struct unpack  quot  lt h quot   wavedata      print int data 0     This snippet reads 1 frame  To read more than one frame  e g   13   use wavedata   wavefile readframes 13  data   struct unpack  quot  lt 13h quot   wavedata

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