Creating, Managing and Playing back Ambisonic Wave Files

For this tutorial the following tools will be needed (all free!)

Ambisonic Wave Files

Once a mix has been created using the tools described in this Wiki (i.e. Soundscape + Audiomulch, or Reaper, all combined with the Ambisonic VST Plug-ins). The best way to distribute, or archive this mix is by recording the outputs of the B-format busses (i.e. W, X, Y and Z for 1st order Ambisonics, for example). These will normally be exported from Reaper or Audiomulch as multiple mono wave files (although Audiomulch will actually output straight to a multi-channel interleaved file, see later!)

Once these mono files have been rendered, we want to actually create a multi-channel, interleaved file that is also known to be B-format. This is important so that:
  • The channels will always be 'in sync' with each other, as they are interleaved in one file.
  • Packages recognise that it is a B-format file and so shouldn't feed the B-format channels directly to a speaker output

AudacityPrefsCropped.JPGThe specification for a B-format Waveformat Extensible is detailed at Richard Dobson's website, where he has basically specified a Globallly Unique Identifier to 'tag' the file as B-format (see also Multiple Channel Audio Data and WAVE Files).

To create a multi-channel file from four mono files, we could use Richard Dobson's tools, but we will use Audacity as it has a friendly graphical user interface, and allows other editing to be carried out.

Audacity

Install and open Audacity (be sure to install the latest, beta, version - currerently 1.3.3beta). In order to allow multi-channel wave files to be exported, we must enable the "Use Advanced Mixing Options" in the "File Formats" menu as shown to the right.

Once this has been done, your B-format files can be 'dragged' into Audacity. Make sure the ordering of the channels are W, X, Y followed by Z. An example is shown on the right.Audacity4Channels_50pc.JPG

Now we need to export the wave file. Select File->export->wave and the channel mapping dialogue box will appear as shown below. The default settings (1 to 1 mapping of input to output) will be fine.


AudacityRouting_50pc.JPG

Next, click ok and choose a file name for your 4-channel wave file.

At this point a 4-channel wave file has been created, but we haven't marked it as "B-format" yet. In order to do this we must use the command line Multi-channel Toolkit written by Richard Dobson.

Richard Dobson's Multi-Channel Toolkit

Extract the tools to the same directory as your wave file (or move the wave file into the directory where the tools are located) and open a command line prompt (hit Start->Run and type "cmd" from Windows).

Change directory to the directory containing the tools and the wave file by typing (where "d" is the drive name)
d:
cd d:\directory name


Now type the following command to convert your wave file to B-format (where four.wav is the wave file created with Audacity and bformat.wav is the B-format resulting wave file)
copysfx -t5 four.wav bformat.wav

Double clicking this new wave file will result in Windows Media Player looking for a codec and then returning an error saying "Codec not available". In order to fix this problem, download and install the plug-in for Windows Media Player from here (make sure you choose one that matches your setup, or if you just want to test it in stereo, download the Quad decoder).

You have now created and listened to your first B-format wave file! Please list any problems with this tutorial in the discussion page.....