Ever wanted to create surround sound from your own stereo audio files using off the shelf software like Cool Edit Pro, Sound Forge, or Wave Lab etc... Well it's a lot simpler than you think. We are talking about simulating Dolby Pro Logic and nothing will take the place of a real Dolby Encoder, but with all that said you can still experiment and use this technique in your own recordings. You can't really control where things will be placed when it's played back on a surround sound system.

You don't need to use the center channel or you can create the center channel using the summation of the left front and right front channels. As you probably aware that the less you process a sound the less distortion is added. Pro Logic encoding changes the phase relationships within the sound and does add distortion. Dolby makes digital ones but I would go and rent (or look on EBAY) a Dolby SEU4 Surround Encoder and route all four track out of the computer into the encoder and record them back into the computer and use the resulting file. The encoder does need to be calibrated but most rentals do that. I would check it to on the safe side.

You don't need the decoder but you should at least monitor using a Pro Logic system.

Or...

If you want to do a Pro Logic Mix and don't really have any panning then you do the following:

1. Sum both the left and right surround tracks together. If the tracks are low enough You can apply the -6 dB gain to both tracks after summation to prevent clipping. Otherwise reduce the gain before you add them together. You will end up with a stereo file where the left and right channels contain the same information.

2. Then INVERT the Polarity (Phase) of the Right Channel of the resulting stereo file. This track contains the Difference of the summed stereo track and will be routed directly to the surrounds in a Pro Logic System. It probably won't sound like you think it will. IMHO You don't need to apply a 100 Hz Hi-Pass and 7k Low-Pass filter to the resulting file. Do so only if you hear sibilance or if there is a lot of low frequency content in the surround track. 3. The Pro Logic Decoder will create the center as you probably already know.