Hello everybody!

I am a sound design student. I am exploring the subject of history of sound formats, especially Split Surround. Unfortunately, there is not enough information for me to understand this concept. I thought it is a good idea to ask this question here. While researching I found an article that confused me even more:

"Split Surround was compatible with the Baby Boom format. Like Baby Boom, Split Surround had the same left, center, right, mono surround, and two boom tracks. The added left and right surrounds were put on the same tracks as the two boom tracks. This was accomplished by limiting the boom tracks to under 200 Hz and the left and right surrounds were limited to about 500 Hz."

Split Surround was the first 5.1 as we know it today (http://frank.mtsu.edu/~smpte/seventies.html) As far as I am aware 5.1 means 5 channels (left, center, right, left surround, right surround) + a sub-bass channel. Why then Split Surround used two boom channels? What is Mono Surround? What was the speakers setup of Split Surround?

I will be grateful for explaining me this abstruse concept. Many thanks in advance

2 Answers 2


Split surround wasn't the first "5.1." It wasn't even the first surround format. "5.1" is a term created by Tomlinson Holman to describe a particular surround format (the one that most people today are familiar with). Various other formats have been tested over the decades, and they were all experiments as to what people thought would work. Someone though having two low frequency channels would be important and tried it.

Mono surround is exactly what it sounds like. Instead of having a left surround and right surround channel (that plays out of the surround speakers on the left and right respectively), there was a single channel of audio content that would play out of all surround speakers (regardless of spatial location). The original Dolby Pro Logic format used a mono surround channel as well.


You can find an interesting discussion of "Baby Boom" and Split Surround" and other terms relating to 70mm release prints with magnetic sound here:


These formats had 6.0, 4.1, 6.1, and other layouts. There's a chart here:


These 70mm formats from the late 1970s were for limited premium "road show" releases. They preceded the 5.1 revolution and gave experience to the engineers who designed the several 5.1 formats as to what worked well and what didn't. Dolby Digital, DTS and SDDS are all digital formats, which also contain an analog Dolby Stereo SR track for compatibility and as a backup.

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