What would "S&D" stand for on a shelving EQ? For instance on the Olympic Studio1 console EQ

[InterstellarObscure]

Not sure if it's the right forum for my question, but was looking at a photo showing the Olympic, Studio 1 console EQ, and hoping to satisfy my curiosity about it. This might be the only close up photo showing the studio1 module; found here on the forums. The studio1 module is on the far left, with the silver-skirted knobs:

First there's the input gain switch and then a high frequency cut/boost switch (maybe it's 10kHz like the Helios beside it).
Third control is a "Fine Gain" pot, not sure what that's for.
Fourth control appears to be a two position switch for "Nor" or "S & D". Is it related to the Mid-Frequency Peak/Trough switch on later Helios EQs?
Last is the Low Frequency cut/boost at 250 or 60Hz.

I've always been intrigued by this partially-Germanium Olympic console, being used to record so many classic records, and apparently being a favorite among many musicians of that era.

Do you have an idea of what these controls might be doing?

 

[k brown]

Not sure how it might apply to an EQ, but my first thought was "Normal" (as in normal stereo), and "Sum & Difference", possibly for EQing a Mid-Side recording?.

https://www.uaudio.com/blog/mid-sid...yNBtC0x-X_5X_tlYQZb4KlEY4L6fV-jiPfJfWJ2VapAvS

Is it a stereo unit?

 

[InterstellarObscure]

but my first thought was "Normal" (as in normal stereo), and "Sum & Difference", possibly for EQing a Mid-Side recording?

Yep, that seems right. Sum and Difference.

don't think these were stereo channels, so I guess Sum and Difference will be analogous to Peak/Trough (aka Boost/Cut)?

The only thing is, on the Helios, you are selecting for either Peak or Trough, whereas here it's Sum+Diff vs. "Nor(mal)." Perhaps it's an EQ on/off switch, where "S+D" engages the Boost/Cut circuit and "Normal" disengages it.

That still leaves the "Fine Gain", Att/Boost pot for either the high or low band I presume. There doesn't seem to be a mid band on these channels, only one inductor for the low band.

 

[k brown]

If not a stereo device, then S & D can't stand for Sum & Difference.

 

[Brian Roth]

Most likely........"fine gain" tweaks mic preamp gain between those 10 dB steps on the switch directly above that control. IE....range of -12 dB to +12 dB from the value selected on the main switch.

Bri