Python - downsampling wav audio file
I have to dump a wav file from 44100Hz to 16000Hz without using any external python libraries, so it is advisable wave
and / or audioop
. I tried to just change the frame rate of the wav files to 16000 using the function setframerate
, but that just slows down the whole recording. How can I just reduce the size of the audio file to 16 kHz and keep the same audio length?
Thank you in advance
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Thanks everyone for your answers. I found the solution already and it works really well. Here's the whole function.
def downsampleWav(src, dst, inrate=44100, outrate=16000, inchannels=2, outchannels=1):
if not os.path.exists(src):
print 'Source not found!'
return False
if not os.path.exists(os.path.dirname(dst)):
os.makedirs(os.path.dirname(dst))
try:
s_read = wave.open(src, 'r')
s_write = wave.open(dst, 'w')
except:
print 'Failed to open files!'
return False
n_frames = s_read.getnframes()
data = s_read.readframes(n_frames)
try:
converted = audioop.ratecv(data, 2, inchannels, inrate, outrate, None)
if outchannels == 1:
converted = audioop.tomono(converted[0], 2, 1, 0)
except:
print 'Failed to downsample wav'
return False
try:
s_write.setparams((outchannels, 2, outrate, 0, 'NONE', 'Uncompressed'))
s_write.writeframes(converted)
except:
print 'Failed to write wav'
return False
try:
s_read.close()
s_write.close()
except:
print 'Failed to close wav files'
return False
return True
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You can use resample in scipy
. This is a bit of a headache because there is some type conversion between bytestring
native in python and the arrays needed in scipy
. There's another headache because there is no way in the Python wave module to know if the data is signed or not (only if it's 8 or 16 bits). It may (should) work for both, but I haven't tested it.
Here's a little program that converts (unsigned) 8 and 16 bits mono from 44.1 to 16. If you have stereo or use other formats, it shouldn't be difficult to adapt. Edit the I / O names at the beginning of the code. Never had to use command line arguments.
#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
# downsample.py
#
# Copyright 2015 John Coppens <john@jcoppens.com>
#
# 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 Street, Fifth Floor, Boston,
# MA 02110-1301, USA.
#
#
inwave = "sine_44k.wav"
outwave = "sine_16k.wav"
import wave
import numpy as np
import scipy.signal as sps
class DownSample():
def __init__(self):
self.in_rate = 44100.0
self.out_rate = 16000.0
def open_file(self, fname):
try:
self.in_wav = wave.open(fname)
except:
print("Cannot open wav file (%s)" % fname)
return False
if self.in_wav.getframerate() != self.in_rate:
print("Frame rate is not %d (it %d)" % \
(self.in_rate, self.in_wav.getframerate()))
return False
self.in_nframes = self.in_wav.getnframes()
print("Frames: %d" % self.in_wav.getnframes())
if self.in_wav.getsampwidth() == 1:
self.nptype = np.uint8
elif self.in_wav.getsampwidth() == 2:
self.nptype = np.uint16
return True
def resample(self, fname):
self.out_wav = wave.open(fname, "w")
self.out_wav.setframerate(self.out_rate)
self.out_wav.setnchannels(self.in_wav.getnchannels())
self.out_wav.setsampwidth (self.in_wav.getsampwidth())
self.out_wav.setnframes(1)
print("Nr output channels: %d" % self.out_wav.getnchannels())
audio = self.in_wav.readframes(self.in_nframes)
nroutsamples = round(len(audio) * self.out_rate/self.in_rate)
print("Nr output samples: %d" % nroutsamples)
audio_out = sps.resample(np.fromstring(audio, self.nptype), nroutsamples)
audio_out = audio_out.astype(self.nptype)
self.out_wav.writeframes(audio_out.copy(order='C'))
self.out_wav.close()
def main():
ds = DownSample()
if not ds.open_file(inwave): return 1
ds.resample(outwave)
return 0
if __name__ == '__main__':
main()
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You can use Librosa's load function (),
import librosa
y, s = librosa.load('test.wav', sr=8000) # Downsample 44.1kHz to 8kHz
The extra effort to install Librosa is probably well worth the trouble.
Pro-tip: when installing Librosa on Anaconda you need to install ffmpeg , so
pip install librosa
conda install -c conda-forge ffmpeg
This will save you the NoBackendError () error.
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