Sampling from direct channels of a movie in MKV format

Posted on by

While working on my last track I worked out some excellent methods for sampling audio from movies. This process allows me to sample a specific channel of the movie, rather then having the entire audio stream flattened out to stereo and then sampling from there.

The reason this can be beneficial is due to how audio is generally stored on a movie. A “5.1” channel movie means you have 6 channels, there is your standard left and right speakers, your left and right surround (back) speakers, your sub/bass, and the key ingredient here, the center channel.

The center channel is generally used for voices, so by being able to sample from specific channels, we can now isolate to just the vocals, or remove the vocals from the mix depending on what we are trying to sample.

All the tools I use here are freeware. The movies of course are not freeware, and remember that [copyright blah blah blah].

This is just going to be a high level overview. I’ll leave it to anyone reading this to google shit and figure out the usage themselves.

Tools Used:

  • Audacity 1.3.13 (Beta) – Make sure to get the beta
  • Ffmpeg For Audacity – To open DTS/AC3 files.
  • MKVtoolnix – To split audio from MKV files
  • MKVExtractGUI2 – GUI for demuxing in MKVtoolnix

Steps:

  1. Install Audacity
  2. In Audacity you need to install FFmpeg. Goto Preferences->Libraries, you get the download link from there and then you just set the directory once it’s installed.
  3. Install MKV tools
  4. Run MKVExtractGUI2 and pick your MKV file
  5. The idea behind this program is that will take your MKV file and separate it into all it’s parts. Once you pick the file, all the parts (Video, Audio, Subtitles, etc) should appear in the window with checkboxes. We only need the audio so we check just this. If the movie has multiple languages you will see them all, just pick the one(s) you want.
  6. Your output should be an AC3 or DTS file, or something similar to that. If you completed the ffmpeg installation correctly, these should now be openable in Audacity.
  7. You will get a multirack file in Audacity with 6 mono channels.
  8. Order of channels should be L / R / C / S / LS / RS.

Enjoy!