Surround Downmix Experimental Method

Hi. This time, I wanted to write and share a template I made quite some time back, in Pro Tools for a downmix based on a 1992 proposition put forth by Michael Gerzon at AES in San Francisco. The idea behind this was to have a bit more width to the stereo mixdown compared to the standard one. Now, this is all purely experimental on my end and it seems to work very well on headphones as well. But I would invite you all to download this and try it out to experiment for your own conclusions. After all, a hive mind is always better than one!

The Mixdown Method

The method employed is as follows. (You can find the reference for this in Spacial Audio – Francis Rumsey) Gerzon proposed an alternative downmix formula based on 5.0 tracks:

L0 = 0.8536L + 0.5C – 0.1464R + 0.3536k(LS + RS) + 0.3536k2(LS – RS)
R0 = -0.1464L + 0.5C + 0.8536R + 0.3536k(LS + RS) – 0.3536k2(LS – RS)

where the suggested k and k2 value is
k = 0.5
k2 = 1.1314

If you convert that to fader levels for Pro Tools, it would become:

L0 = -.68dBL + -3dBC + phase-8.35dBR+ -4.52*k*dB(Ls+Rs) + -4.52*k2*(Ls-Rs)
R0 = phase-8.35dBL + -3dbC + -.68dBR + -4.52*k*dB(Ls+Rs) +p( -4.52*k2*(Ls-Rs))
Note: I am open to corrections if you find any fault. 

The Pro Tools Session

In the template, I have kept the phase inverted signal to 0 rather than -8.3dB just because it felt good to listen to that. But please experiment with that for Mono compatibility as well. I also added the LFE at -12 dB to taste. The way the Template is set up is the top track is where you drop your 5.1 audio. This then goes through the matrix as you can see. You can choose to monitor either the Gerzon version or the regular downmix by alternately muting the 5.1 and the MixDownRegular. The 5.1 track when unmuted will give you the Gerzon version and when muted and the aux below is unmuted will give you the regular downmix.

Additionally, the two masters for Ls+Rs and Ls-Rs are at -2.2 dB. Changing that will change the spacial width of the surrounds that are added into the downmix.

Happy experimenting!

Download here:
Gerzon 5.1 Downmix Template

FM