Read in a wav file and get amplitudes - audio

Question

I need to extract the amplitudes of a wav file and want to do it as a simple commandline app. What's an easy way to do that? Cross-platform would be great. Needs to at least work on windows.
You can download an audio file for testing from soundcloud (or from https://dl.dropboxusercontent.com/u/313647/hosted/one_pos_to_neg_crossing.wav until soundcloud processes it).
Some libraries for potential use:
.NET
NAudio
Python
scipy.io.wavfile
pydub
PySoundFile
friture
snack

Answer 1

Here is a solution I came up with using Accord.NET:
public IEnumerable<float> AmplitudesFromFile(string fileName)
{
Accord.Audio.Formats.WaveDecoder sourceDecoder = new Accord.Audio.Formats.WaveDecoder(fileName);
Signal sourceSignal = sourceDecoder.Decode();
for (int i = 0; i < sourceSignal.Samples; i++) yield return sourceSignal.GetSample(1, i);
}
Project Page: http://accord-framework.net/
Documentation: http://accord-framework.net/docs/Index.html

Answer 2

Here's the first way I figured out how to do it with NAudio.
Output
>SoundToAmplitudes.exe w:\materials\audio\one_pos_to_neg_crossing.wav
0.04284668
-0.005615234
-0.1177368
Code
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using NAudio.Wave;
namespace SoundToAmplitudes {
class Program {
private static int Main(string[] args) {
#if DEBUG
Console.WriteLine(String.Join(", ", args));
args = new[] { #"W:\materials\audio\one_pos_to_neg_crossing.wav" };
#endif
return Cli(args);
}
static int Cli(string[] args) {
string fileName = args[0];
var soundFile = new FileInfo(fileName);
foreach (float s in AmplitudesFromFile(soundFile)) {
Console.WriteLine(s);
}
//Console.WriteLine();
#if DEBUG
Console.Read();
#endif
return 0;
}
public static IEnumerable<float> AmplitudesFromFile(FileInfo soundFile) {
var reader = new AudioFileReader(soundFile.FullName);
int count = 4096; // arbitrary
float[] buffer = new float[count];
int offset = 0;
int numRead = 0;
while ((numRead = reader.Read(buffer, offset, count)) > 0) {
foreach (float amp in buffer.Take(numRead)) {
yield return amp;
}
}
}
}
}

Answer 3

Here's one way to do it in python (using scipy), although I assume that the wav file is 16-bit.
Output
W:\>python amplitudes.py w:\materials\audio\one_pos_to_neg_crossing.wav
0.0428479873043
-0.00561540574358
-0.117740409558
Code
"""Usage:
amplitudes WAV_FILE
Returns the (linear) amplitude of the signal inside the wav file, sample by sample.
"""
from __future__ import division
import docopt
import scipy.io.wavfile
MAX_WAV16_AMP = 32767 # = 2**15-1 # because wav16 is signed (wav8 isn't)
def main():
args = docopt.docopt(__doc__)
one_pos_to_neg_crossing_path = r"W:\materials\audio\one_pos_to_neg_crossing.wav"
if False: args['WAV_FILE'] = one_pos_to_neg_crossing_path
rate, amp_arr = scipy.io.wavfile.read(args['WAV_FILE'])
for amp in (amp_arr / MAX_WAV16_AMP):
print amp
if __name__ == '__main__':
main()
See also
Reading *.wav files in Python
Extracting an amplitude list from *.wav file for use in Python