Using the Precision MS Matrix for Mono Crossover LF Blending

[mediatechnology]

Thank You for the confirmation, I just finish read and learn Your explanation slowly and carefully, so the difference between 2 version that You create: the last one is using balance filter and the the first one is unbalanced filter right?

The second one can be used with either a balanced or unbalanced filter. It's a little more refined using balanced I/O and the precision inverter but does indeed use both halves.

If you switch resistors in the first example you will want to always have the largest value in circuit and then use a switch to parallel the values to raise the frequency. The reason for that is that they provide the bias current for the op amp. In addition the overall filter input needs to see a DC path to ground: The previous stage provides that.

I do understand why you would want an EE in the monitor path.

The choice of op amps is pretty flexible.

[Nescafe]

Hi Wayne,

Thank's again for the resistor explanation, got it. And what I mean with EE in the monitor box is not because I use it for monitoring, the EE is for processing, but since it only need a half of MS card, I use the other half as M/S encoder in my monitoring control box that's because I cannot cut the card into 2 pieces

[mediatechnology]

And what I mean with EE in the monitor box is not because I use it for monitoring, the EE is for processing, but since it only need a half of MS card, I use the other half as M/S encoder in my monitoring control box that's because I cannot cut the card into 2 pieces

Got it.

My working theory is that a good EE for mono LF crossover/LF blending might benefit smaller speaker systems particularly those using a sub-woofer. As I understand it most mono subs use LF addition (like the EE70/77) which effectively subtracts difference information rather than folding L>R and R>L at LF like the VAB84. With really small speakers it forces both pistons to work together.

[Nescafe]

Ah....I just realize that, Thank's Wayne.

[mediatechnology]

I had a chance to revisit the subject of elliptical equalizers to provide low frequency crossover to mono for vinyl mastering, improved ear-bud/headphone listening and improved small-speaker and subwoofer performance.

My working theory is that the steering of side information to the opposing channel used in the original Neumann VAB-84 is superior to the subtractive method used in the EE-70, EE-77 and simple L+R methods to derive Mono at low frequencies.

The original VAB-84 had a sliding -6dB/Octave filter. In its original application, Direct Metal Mastering, the sliding filter made sense.
It was discovered however that the steering technology used in the VAB-84 permits higher-order filters making a sliding filter unnecessary.
The "EE-84" (my shorthand for a VAB-84 elliptical equalizer) uses a fixed frequency filter with either 12 or 18 dB per octave slope.

This a crosstalk comparison curve showing a "subtractive" EE-70 (emulated) -6dB response versus a -12dB and -18dB per octave filters in a "steering" "EE-84" (VAB-84 but higher-order) configuration.

Crosstalk Curves

EE-77 subtractive vs. EE-84 steering mono crossover comparison.

Reference level was approx -5dB full scale.
When crossover to mono occurs, the signal is split equally between channels.
Thus, the response converges to approx -12 dB FS.

The mono sum for the "EE-84" (high-order VAB-84 emulator) is always unity.
There is no "phase hole" in mono.

The higher filter orders of the "EE-84" do not compromise mid range imaging and sound far more transparent than does the EE-77.

[emrr]

It makes sense to me the higher order filter would be better in this application. Good post.

[mediatechnology]

Thanks Doug.

I'm starting to think that 150 or 300 Hz both -18dB/octave would be about all the choices one would need.

[Gold]

I think this is the same test you sent me sound files from, Wayne. I found the EE77 more effective at controlling vertical modulation on the lathe than the VAB84 approach. From the graph it looks like there is 2dB or so more attenuation around 40Hz or so. I think this accounts for it. If the steeper filters could have the same or more attenuation around 40Hz it would beat the EE77 both in sound and function.

[mediatechnology]

Paul -

Thanks for posting.
Those latest curves used a slightly different test fixture for both approaches.
I went back and looked and the "VAB-84" example sound files were using the -12dB/octave test circuit.

I think there is also a slight LF response error in the previous EE-77 curve at LF since the "EE-77" has a slight LF rolloff (an insertion loss) in addition to the blending. I didn't gain match those too closely either.
The VAB-version was DC-coupled throughout in the test giving it more overall low-end.
That may be the 2 dB or so difference you see at 40 Hz.

I agree thinking that -18dB/octave is the way to go for the VAB-84 emulator because it carves out more vertical at LF then gets out of the way faster in the transition to the mid range. With the steeper slope the cross-over frequency can be moved higher to carve out a bigger swath of vertical information.

[emrr]

Paul, great to hear your experienced comments on this.