In the case where the low frequency uncorrelated information is small there is no reason to switch it in. The lathe automation can take care of it. You need to use it when there is a lot.
True.
What I also found is that the LF is highly uncorrelated it should be mono'd regardless of whether it's going to wind up on vinyl.
Having something fully-centered at LF when played back on speakers effectively doubles the LF driver area vs. something panned hard to one side.
On 'phones it takes LF that would sound slightly outside the head and centers them inside the head.
The LF is more "focused" and more suited for playback on smaller speakers.
How does the result of this method differ from a 6dB/oct slope on the side channel?
A 6 dB per octave slope on the Side channel using an MS process produces the exact same result as an EE70/77.
A steeper slope inserted into the Side channel still gives you 6 dB per octave because the filtering is subtractively derived.
I don't see how the EE-series could have been made higher order.
In fact everything I see commercially produced in the modern era is 6 dB per octave. (ADT, Maselec MTC-2)
The VAB84 was 6 dB per octave but can be a higher order with the crosstalk/desired LF blending results also being that order.
I think Neumann may have kept the VAB84 to 6 dB per octave since the filter slid and was constructed with a VCA.
They also may have just not tried anything steeper.
So in addition to having the property of "Flank signal components are simultaneously transferred to the other channel" it can be made with a steeper slope and thus provide a lot of LF blending to mono without affecting the mid-band.
ADT mention that with their box set to 300 Hz (the -15dB separation point) you can begin to hear it.
That's because with a 6 dB per octave slope the separation at 1 kHz is only about 24-25 dB.
This is VAB84 emulation with an 18 dB per octave 50 Hz corner frequency.
VAB84 Emulation Crosstalk/Blending Curve Using the Precision MS Matrix With An 18 dB Per Octave Slope
You can't hear the steepness of the higher-order filter but it sure gets out of the midrange fast and can be made much higher in frequency without affecting the midrange if the source material requires it.
Okay, now I think I understand it. It's pretty cool. I would like to hear it. If you eliminate the inverter do you get the subtraction of the side channel? If so you could put a switch in.
Here's another weird aspect. If you take the inverter out of the Left channel and move it to the right - effectively inverting Side - then you get an odd LF comb filtering phase cancellation effect that is not useful.
I haven't figured out a way to switch it easily (there may be one) since one topology (MS Side filtering) injects Side into Mid and the other (VAB84) injects filtered Side into Left and Right. It might be a complex switch.
Using the MS matrix board to do the VAB84 emulation uses the "Decode" half of the board leaving the "Encode" available for a conventional Side HP filter.
It might be easier to switch outputs to change methods.
Thanks for looking at this Paul.
I'll try to figure out a way for you and all of us to listen to it