Stereo to Surround Sound

Ever want to hear your music in surround sound but it's already mixed in stereo?

Well there are a number of tricks you can do to convert your stereo tracks into 5.1 surround sound tracks.

Technique #1:

Use a Dolby Pro-Logic Decoder (or an SRS Hardware Decoder) to decode your stereo track into Left, Center, Right, and Surround channels. From this point you only need to generate two surround channels from a single surround channel. There are a number of ways to divide/create two tracks from a single surround channel but probably the best sound way is to narrowband filters. This will end up creating the Left Surround and Right Surround channels from the Dolby Pro Logic decoded surround track. First the best type of filter is Parametric. The 'Q' setting should be and "listen" to the mix and tune into a particular frequency. If you boost the frequency in one side you should cut the frequency in the other. SRS Labs hardware decoders for converting mono or stereo signals into 5.1 using a function called Xtract.

Technique #2:

You can also try using of early reflections and reverb. This is base upon the well known Haas Effect which is that the first sound source heard by the is the one that is used to tell where the sound is coming from.

You again use the difference information found with subtracting the Left channel from the Right channel (Left - Right). This creates a mono signal that contains both left and right channels except all of the center channel (appearing in both speakers) is removed. This is how many of the earlier karaoke vocal remover system worked. So any sound that appears equally in both the left and right channels is cancelled out (L-R). You are left with what is called the difference information.

Next you take this mono difference channel and run it through a stereo reverb/early reflections generator which will give you a simulated stereo result. The idea is to get a non-correlated (not the exact same) stereo output. If you are using a digital audio editor then you can use the same mono reverb with different settings, ie. distance and surface conditions. Route the mono output of one reverb to the Left Surround channel and the the output of the other to the Right Surround channel.

For the Center Front speaker you simply add the Left Front and Right Front channels together. For music only conversion you can lower the volume of the center speaker anywhere from -6dB to -12dB. You can also remove some of the low frequencies (below 50Hz) from that speaker as well. Because of the Center Front speaker's location you may need to lower frequencies between 2.2kHz and 3kHz by about -3dB or so. This will keep the width of the front speakers wide as the Center Front speaker will tend to collapse the "Stereo" soundfield.

Other Ways of Converting Stereo To 5.1 Surround can be found:

TC Electronic's Unwrap Algorithm used in the TC Electronic System 6000 Audio Processor.

Z-Systems z-K6 K-Surround Stereo-to-Surround Processor also you can use an SRS Labs hardware decoders for converting mono or stereo signals into 5.1 using a function called Xtract.