Mid Side M-S Matrix Uses No Precision Resistors

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mediatechnology
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Re: Mid Side M-S Matrix Uses No Precision Resistors

Post by mediatechnology » Mon Aug 03, 2020 12:32 pm

By the way, would you like to hear about my concept for the vertical noise monitoring? Ie useful for listening to the deleted info to try and discern if there is still music and you should choose a lower frequency? I think I realized a good way to do it.
I would.

This might be a good place for it: viewtopic.php?f=6&t=828
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Re: Mid Side M-S Matrix Uses No Precision Resistors

Post by mediatechnology » Tue Aug 04, 2020 6:30 am

Kevin -

It occurred to me that the best way to obtain inverted copies of the input would be to use cross-coupled line receivers.
Using cross-coupled inputs, both inverted and non-inverted signals are available with identical phase shifts.
This also permits feeding the matrix with unbalanced sources.

With an inverted copy of the Right input available, a differential connection using a 1243 or 1246 allows L+R in the form of {L-(-R)}.
It uses a lot more line receivers but since you're interest is virtual simulation and would never be built there isn't any overhead.
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Re: Mid Side M-S Matrix Uses No Precision Resistors

Post by KMN » Tue Aug 04, 2020 12:01 pm

mediatechnology wrote:
Tue Aug 04, 2020 6:30 am
It occurred to me that the best way to obtain inverted copies of the input would be to use cross-coupled line receivers. Using cross-coupled inputs, both inverted and non-inverted signals are available with identical phase shifts
Yes this is what I have been doing since I have a balanced/differential front end to feed it with, both polarities are already available. I am really sold on your ina style front end, using cross coupled line recievers, so I use that topology. Also, I believe, please correct me if I'm wrong, doing the conversions differentially can produce up to another 6dB of separation over the single ended conversions.

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Re: Mid Side M-S Matrix Uses No Precision Resistors

Post by mediatechnology » Tue Aug 04, 2020 12:04 pm

You can also do the Mid and Side Extraction using cross-coupled stages to obtain anti-polarity outputs to feed the insert.

Not sure that cross-coupling would give you an extra 6 dB separation but it would increase headroom.
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Re: Mid Side M-S Matrix Uses No Precision Resistors

Post by KMN » Tue Aug 04, 2020 12:10 pm

Thank you for your comments, sir!

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Re: Mid Side M-S Matrix Uses No Precision Resistors

Post by Gold » Wed Dec 15, 2021 2:01 pm

I would like to use the Encode half of the M/S board(s) in my monitor controller for Mono and Difference. The Monitor Controller uses a balanced H pad with a 10K input impedance when both are fed in parallel. I would like the input to the M/S board to have an input impedance of 100K so the input still looks like about 10K to any source. Since the 124x has an input impedance of about 10K it won't work. The two ideas I've come up with so far are either a four resistor single opamp receiver with 100K input resistors and 50K feedback resistors or a 2:1 input transformer into an inverting opamp unity gain stage. Each feeding the M/S Encode matrix. What's the best way to accomplish this?

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Re: Mid Side M-S Matrix Uses No Precision Resistors

Post by mediatechnology » Wed Dec 15, 2021 2:25 pm

Paul - Wouldn't you want to put the MS pre-pad?
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Re: Mid Side M-S Matrix Uses No Precision Resistors

Post by Gold » Wed Dec 15, 2021 3:35 pm

I'm trying to mimic the specified 1246 input with a 6dB pad. Shouldn't I be doing that for center channel headroom? If the 1246 could be made to have a 100K input impedance I'd be good.

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Re: Mid Side M-S Matrix Uses No Precision Resistors

Post by mediatechnology » Wed Dec 15, 2021 4:46 pm

I'm suggesting that you put the MS encoder, to monitor Mono or Difference, ahead of the Monitor attenuator.
That way you have a low impedance source to drive the H-pad and you don't have to worry about the MS loading the pad.

What advantage is there to it being post?

If it has to be post I would use a voltage-follower buffer at the input to the line encoder's line receiver.
Since it's balanced you'd need 4 followers.
Though we'd usually worry about common mode distortion in a follower it's monitoring mono or side and isn't in the main path - it's in a confidence monitoring/diagnostic path.
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Re: Mid Side M-S Matrix Uses No Precision Resistors

Post by Gold » Wed Dec 15, 2021 4:59 pm

mediatechnology wrote:
Wed Dec 15, 2021 4:46 pm
I'm suggesting that you put the MS encoder, to monitor Mono or Difference, ahead of the Monitor attenuator.
That way you have a low impedance source to drive the H-pad and you don't have to worry about the MS loading the pad.

What advantage is there to it being post?
It is ahead of the monitor attenuator but is fed in parallel to the attenuator from a source. If monitoring stereo the input to the attenuator is passive. If monitoring Sum or Difference the input to the attenuator is from the M/S board. The monitor needs to stay passive. Putting the M/S board in series with the attenuator input is a no go.
If it has to be post I would use a voltage-follower buffer at the input to the line encoder's line receiver.
Since it's balanced you'd need 4 followers.
Though we'd usually worry about common mode distortion in a follower it's monitoring mono or side and isn't in the main path - it's in a confidence monitoring/diagnostic path.
I guess the 2:1 transformer with a voltage follower is the best solution. I suppose if I use an 8 pole switch I could switch both the Inputs and Outputs of the M/S board. I think that would work too.

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