The Studer "90°" Dome Filter Stereo to Mono Quadrature Summer

[mediatechnology]

Putting the final touches on the "Quadrature Summing Filter" board.



I eliminated the relay which forwarded I and Q as "stereo" to the final output.
That would almost never be used except for people wanting to do sin cos detection and draw flower petals on the oscilloscope.
I provided the separate I and Q outputs on a header.
The board is 3.7" x 2.75".

[mediatechnology]

This is the current schematic for the "Quadrature Summing FIlter" layout.

I decided to eliminate the ability to route the separate I and Q components to the final outputs to save a relay and board space.
This mode would not be used in most applications.
I and Q now come up on a header where they can be used in a sin/cos output configuration for instrumentation applications.
J1 optionally routes the Left input to both allpass chains for a "one in two out" mode.



The board is 3.7" x 2.75"

[mediatechnology]

Quadrature Summing Filter boards are on order and should be available in about 7-10 days.
I'll be building one to check the layout as soon as they arrive.
The BOM for parts excluding PC board looks to be about $101 US.

[mediatechnology]

While I'm waiting on Quadrature Summing Filter boards to be delivered I fired up the Protoboard to make some sample files.

Some time ago I downloaded a problematic synth sample from Gearspace that was posted in this thread: https://gearspace.com/board/so-much-gea ... oting.html

I hadn't had the opportunity to process that file until now.

The first section is the uber-wide original version which on the vectorscope looks like a big round ball of steel wool.
The second section is conventional (L+R)/2 mono.
The third is I+Q/1.4 mono.

For identical in-polarity inputs the gain is structured so that (L+R)/2 is unity gain and (I+Q)/1.4 is also unity gain.
When the inputs are out-of-polarity the conventional mono output has no output.
The (I+Q)/1.4 output - when the inputs are out-of-polarity is also at unity gain.
Thus on the "I+Q" output in-polarity and out-of-polarity fold down to mono with equal weight.

The first section is the uber-wide original version which on the vectorscope looks like a big round ball of steel wool.
The second section is conventional (L+R)/2 mono.
The third is (I+Q)/1.4 mono.

Quadrature Summing Filter Synth Demo wav file: https://proaudiodesignforum.com/content ... h_Demo.wav


Quadrature Summing Filter Synth Demo

I also tried a fully-uncorrelated noise file: https://proaudiodesignforum.com/content ... e_Demo.wav

The first section is stereo noise.
The second section is conventional (L+R)/2 mono.
The third is (I+Q)/1.4 mono.


Quadrature Summing Filter Uncorrelated Noise Demo

Somehow, as if by "magic" - but actually predictable - the RMS power of the I+Q sum is 3 dB greater than L+R.
The powers of the "stereo" and I+Q segments are statistically identical.

[mediatechnology]

More sound files.

Davie Allan and The Arrows "Shape of Things to Come" originally recorded in LCR. Sequence is Stereo, L+R then I+Q.

https://proaudiodesignforum.com/content ... s_Demo.wav



Once again I+Q has 3 dB more signal power than L+R.