The Dolby Pro Logic Guide
written by Freezy3000

This is a guide for all who want to make Dolby Pro Logic encoded WAV files. I suppose you now what this means. Most of the VHS videos today use such kind of encoding to get two additional channels (center and surround). To decode these channels you need a Dolby Pro Logic decoder. The file you will get is a normal PCM Stereo file.
All you need is a audio software like Cool Edit Pro. In the following example I'll use Cool Edit Pro 1.2.

  1. You must have one stereo file ready for left and right channel and two mono files for center and surround channel.
  2. Open Cool Edit Pro.
  3. Open the stereo file you've got for the front channels (btw all files must have the same sample rate and resolution).
  4. Now adding the center channel: Select Mix Paste from Edit, choose Select File and select the mono file you've got for the center channel. Then pull down the volume to 70.7 percent. Be sure that you blend it over the stereo file to both channels.
  5. Adding surround channel: Again Mix Paste but choose the surround file now. Pull down the volume to 70.7 percent but check that the right channel is inverted.
  6. That's it. Easy huh? ;)

By the way, the main formula is:
Ltot = L + 0.707C + 0.707S
Rtot = R + 0.707C - 0.707S

If you wonder why there is more on the center channel than in the file you used, think that the Pro Logic decoder takes all what's equal on left and right an interprets it as center.

Many thanks to Ventolin.
 12. Oct 1999