The MTC-MS-II: An Improved Precision Mid Side Matrix

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mediatechnology
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Re: The MTC-MS-II: An Improved Precision Mid Side Matrix

Post by mediatechnology »

I got four boards in and the layout and design worked perfectly.
I'll be running some more tests and post the FFTs.

This particular board run seemed to have a slight registration problem which offset the default 0.012" clearance on some holes to the point one pad had a tin whisker short to the ground plane. I had to cut that away with an Xacto. The manufacturer is going to re-do the run and replace all four. But at least I know the layout works. I'll have replacement boards in about a week.
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Re: The MTC-MS-II: An Improved Precision Mid Side Matrix

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I measured the crosstalk performance for full encode-decode with various combinations of Mid Side Gain Offset.

They virtually overlay at Mid/Side at 0dB/0dB, -6dB/0dB, 0dB/+6dB and -6dB/+6dB.
(Numbers are those applied to encode. Decode has a reversed sign.)

Image
MSII Crosstalk vs Mid Side Gain Offset

Keeping the number of stages in the encode/decode paths balanced is the key to consistency.
I chose random THAT1240s and THAT1246s for this test.

I'm happy with the results.
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mediatechnology
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Re: The MTC-MS-II: An Improved Precision Mid Side Matrix

Post by mediatechnology »

Noise Measurements

Image

The unweighted noise floor for full encode/decode is -95 dBu.
The overload point is +27 dBu (±15V supplies) making the Dynamic Range 122 dB.

The A-weighted noise floor is -98 dBu for a Dynamic Range of 125 dB.
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Re: The MTC-MS-II: An Improved Precision Mid Side Matrix

Post by mediatechnology »

Image
The MTC-MS-II second-generation precision Mid Side Matrix.
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Re: The MTC-MS-II: An Improved Precision Mid Side Matrix

Post by mediatechnology »

I'm really enjoying the Side Tilt EQ in this thing. I have absolutely no clue how effective stereo Tilt EQ would be on L/R material but on Side it is very, very useful.

The Tilt EQ's property that lowers the LF as the HF is boosted is ideal in this application.
Pardon the pun but a HF shelving EQ in this application just doesn't "cut" it.

Adding HF Width provides a nice sparkle sort of like mild EQ with additional "air" or space.
Not a lot of Tilt is needed to add "pop" on panned shakers, percussion etc. and the smooth gentle curve of the Tilt is far more preferable than surgical EQ.
Because it cuts LF as it boosts HF it's easy to add HF Width without adding LF woolly-ness.

For older early stereo material that was released with hard-panned elements, the Tilt and Width controls can be used to move things back to center-stage. Recordings with a perspective that sounded like you were on-stage standing between the drummer and upright bass can be modified to move the listener back into the front row. Reducing width on this type of material makes it sound more focused.

Bass elements just sound better when both speakers are reproducing them.

The Side Tilt EQ process is a derived subtractive filter.
The maximum change in Width/Crosstalk is 6 dB/octave regardless of the filter slope so anything steeper doesn't provide benefit. Less is more.

A little Tilt goes a long way so the +/-3 dB range is about right.
I measure the maximum slope of the Tilt to be about 5 dB/octave in the midrange when full +/-3dB boost cut is used.

Whatever is done to modify Width does not affect mono fold-down.
I would also caution that using Side Tilt as corrective EQ disappears in mono.
When the mono button is pressed the sound reverts to its original state.

When I get the chance I build up a stereo Tilt EQ using the same circuit and give it a listen.

In the meantime I'll be posting some wiring suggestions for the Tilt EQ potentiometer (or stepped switch) in the MSII "Build" thread.

(To make a long story short you want to use 3 conductor plus shield for the Tilt EQ control with the three conductors used for the CW, Wiper, and CCW terminals and the shield grounded at one end for electrostatic shielding.)

W
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Re: The MTC-MS-II: An Improved Precision Mid Side Matrix

Post by billshurv »

Hmm interesting. Sounds like it might have an application as an improved domestic tone control. I could be tempted...
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Re: The MTC-MS-II: An Improved Precision Mid Side Matrix

Post by mediatechnology »

Bill, you might want to have a look at this thread on the Ambler Tilt EQ this one is based on: viewtopic.php?f=6&t=732
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Re: The MTC-MS-II: An Improved Precision Mid Side Matrix

Post by billshurv »

I had read that, as been intrigued by tilt ever since John Crabbe did a piece on a passive tilt EQ you could build at home. He was possibly the last of the old skool hifi mag editors and is sadly missed. But I don't think anyone has ever considered doing side Tilt EQ for domestic tweaking. It warrants consideration (and possibly its own thread). But your comment about hard panned stereo struck a chord as this does sometimes annoy me.
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Re: The MTC-MS-II: An Improved Precision Mid Side Matrix

Post by mediatechnology »

Derek Bowers published a passive one in Electronic Design. I just checked the ED website and they have the article minus figures.

I'll scan my original copy and post it. See: https://www.proaudiodesignforum.com/for ... 170#p11170
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