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Mid-Side Spatialization Patch

Posted on | December 24, 2015 | No Comments

This is a mid-side stereo patch explor­ing ways of spread­ing the var­i­ous out­puts from the DPO around the stereo field. The DPO sends 6 wave­forms to the RxMx. The low­er-num­bered RxMx chan­nels are fed fun­da­men­tals, and become the “mid” sig­nal. The high­er chan­nels have increas­ing­ly spec­tral­ly-rich oscil­la­tors, and become the “side” sig­nal.

The first clip has some reverb, ping-pong delay and drums added. The sec­ond clip is the raw patch:

Mid-side decod­ing is:
L = M + S
R = M — S

Maths is used to invert the “Side” sig­nal and sub­tract it from “Mid”. The Optomix is used to add these two togeth­er. That way, we have the L and R sig­nals.

I’m fil­ter­ing the Side sig­nal via the MMG, which allows for fil­ter­sweeps that only hap­pen in stereo. It’s also a good idea to scoop out the fre­quen­cy range occu­pied by the Mid sig­nal with a high­pass so the decod­ed sound isn’t as hol­low. One of the many beau­ties of MS encod­ing is you can do stereo fil­ter­ing (of sorts), using mono fil­ters / effects.

One inter­est­ing part is cal­i­brat­ing the lev­els of chan­nels 2 and 3 on Maths to get the bal­ance right. Set the RxMx chan­nel and radi­ate con­trols so you only hear chan­nel 1. This should be pure “Mid”. Adjust Maths Ch 2 so that the L and R out­puts are the same lev­el. Next, set the RxMx so you only hear chan­nel 6 — this should be pure “Side”. Adjust Ch 3 on Maths in the neg­a­tive until the L and R chan­nels have a rough­ly equal lev­el. The sound should be com­plete­ly phase-invert­ed from left to right.

Now, set­ting chan­nel and radi­ate should mix between mono and stereo imag­ing, with the high­er har­mon­ics appear­ing main­ly in the stereo field. Things can get pret­ty nuts of you tune Oscil­la­tor A and B to dif­fer­ent fre­quen­cies.

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