Mixing many audio files fast and easy

Question

I have to mix audio data for a machine learning task.

The setting is the following: I have two folders of tracks. One contains background files with background noise, the other contains files with a sound to recognise.

Now I have to mix them together to get all permutations between each file from the first folder and each file from the second folder.

To give an example:

• Folder One: b1, b2, b3

• Folder Two: s1, s2, s3

• Mixed Folder: s1b1, s1b2, s1b3, s2b1, s2b2, s2b3, s3b1, s3b2, s3b3

I am currently using Audacity to do this manually, but my deadline is in 8 days and I still have to do this with a couple dozen files.

So my question is if there is some way to automate this?

Or to make this task somewhat less time-consuming?

I know that it would probably be possible with Matlab, but I am searching a faster and easier way, hence I thought to try it here.

---

Here is my solution. I have realized it in C#. Just in case someone stumbles upon this.

class Program
{
    // contains noise file names
    static List<string> noiseFilesDir = new List<string>();
    // contains sound file names
    static List<string> soundFilesDir = new List<string>();

    static string soxRoot = @"C:\Program Files (x86)\sox-14-4-2";

    static void Main(string[] args)
    {
        foreach (string s in Directory.GetFiles(soxRoot + "\\NoiseFiles", "*.wav").Select(Path.GetFileNameWithoutExtension))
        {
            noiseFilesDir.Add(s);
        }
        foreach (string s in Directory.GetFiles(soxRoot + "\\SoundFiles", "*.wav").Select(Path.GetFileNameWithoutExtension))
        {
            soundFilesDir.Add(s);
        }

        var processStartInfo = new ProcessStartInfo();
        processStartInfo.WorkingDirectory = soxRoot;
        processStartInfo.FileName = "cmd.exe";
        processStartInfo.RedirectStandardInput = true;
        processStartInfo.UseShellExecute = false;

        Process proc = Process.Start(processStartInfo);

        using (StreamWriter sw = proc.StandardInput)
        {
            if (sw.BaseStream.CanWrite)
            {
                //sw.WriteLine();
                for (int i = 0; i < soundFilesDir.Count; i++)
                {
                    for (int j = 0; j < noiseFilesDir.Count; j++)
                    {
                        string cmdString = string.Format(@"sox -m SoundFiles\{0}.wav NoiseFiles\{1}.wav MixedFiles\{0}{1}.wav", soundFilesDir[i], noiseFilesDir[j]);
                        sw.WriteLine(cmdString);
                    }
                }
            }
        }
    }
}

Answer 1

Using Sox, you can easily mix two files together by using the command

sox −m input1.wav input2.wav output.wav

This command will already be faster than opening both files in Audacity, and selecting export options.

Now, next step would be to setup a script that will execute this command on all your combinations. Depending on your computer platform, several possibilities exist (bash, python, ...).

As an example, a quick and dirty python script :

import os
import subprocess
from os.path import basename

# directory containing noise files
noiseDir = "/Users/audionuma/Desktop/noise"
# directory containing signal files
signalDir = "/Users/audionuma/Desktop/signal"
# destination directory for mixed files
outputDir = "/Users/audionuma/Desktop/out"

pathsToNoise = [os.path.join(noiseDir,fn) for fn in next(os.walk(noiseDir))[2]]
pathsToSignal = [os.path.join(signalDir,fn) for fn in next(os.walk(signalDir))[2]]

for noisePath in pathsToNoise:
  for signalPath in pathsToSignal:
    outFileName = os.path.splitext(basename(noisePath))[0] + "_" + os.path.splitext(basename(signalPath))[0] + ".wav"
    outFilePath = os.path.join(outputDir, outFileName)
    subprocess.call(["sox", "-m", noisePath, signalPath, outFilePath])