Mid Side M-S Matrix Uses No Precision Resistors

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

Post by Gold » Wed Apr 07, 2010 8:00 pm

Doug,
They are the attenuators for the input and output line amps for the A/B path lacquer mastering console I'm building. +/- 11dB in .5dB steps. They will be potentiometer style. Each two deck switch will control either Left Preview & Left Program or Right Preview & Right Program. Doing it as a bridged T would be better but I had to draw the line somewhere. These switches were expensive. I had Shallco make me a stereo 30 position 10k:5k H attenuator in 1.5dB steps for the monitor. 12 decks. That was expensive too. I think I'm going to make the line amp attenuators 3k. That's as low as I want to go as I haven't decided what will be driving them. Either a DOA or a chip.

The console is getting close. I've been working on it for over three years. I haven't talked about it much in public because it is such a huge project. I didn't know if I could do it when I started. The frame fabrication is almost done. I should have a four channel transfer path done in the next month or two. It will have the In/Out amps, HPF/LPF from the Neumann console (HT75), and an elliptical EQ. Roger did a beautiful job laying out the elliptical EQ board. This will allow me to remove the Neumann console and start using the transfer path for cutting. As I finish the EQ's and compressors I can add them in. Ed Anderson is designing the A/B path switch and crossfader. I hope to have that in June. Then it will be "done". Then on to trying my hand at designing an elaborate HPF/LPF set.

Just to toot my own horn, I believe this will be the most elaborate A/B console ever built. It's going to sound great too. All processing units are four channels. That's eight channels of everything. Each path will have a Barry Porter "net EQ", a Pico SEII, an Igor Sontec and a DAOC. There will also be a Maselec deesser for each path. It's a beast.

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

Post by emrr » Wed Apr 07, 2010 8:08 pm

Get down. Sounds excellent. I was guessing voltage dividers, so I understand the concern. Keep us posted.
Best,

Doug Williams
Electromagnetic Radiation Recorders

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

Post by emrr » Thu Apr 15, 2010 12:28 am

I don't think you are missing anything; maybe I'm missing something. :mrgreen:

I think the crosstalk issue is fairly esoteric, and will have to be proven in practice, as to whether there's significant problems or not. May depend on the type of source material. I'm thinking it won't matter for most things, but I am easily wrong.
Best,

Doug Williams
Electromagnetic Radiation Recorders

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

Post by mediatechnology » Thu Apr 15, 2010 7:15 pm

I think the point is, in mastering, to break the L/R into M/S so you can alter the "crosstalk." (Or image.)

The only justification for the precision mode is for bypass so you can compare it before to what you've done after without the matrix itself altering the "before" and to minimize level from and crosstalk from being a factor in the A/B comparison.

So if you bypass the attenuator when it out what's the harm in having it when its "in?" I see none. Go for it. I don't think you're missing anything.

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

Post by mediatechnology » Sat Apr 17, 2010 9:49 am

I think that in conjunction with dynamics or EQ processing having level trims in the MS domain - a "make-up" gain - would be useful.

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

Post by Gold » Mon Apr 19, 2010 2:38 pm

mediatechnology wrote:I think that in conjunction with dynamics or EQ processing having level trims in the MS domain - a "make-up" gain - would be useful.
Yes. A common usage would be to compress the M channel to knock back a vocal and then use gain to bring the balance back. Or cut some woofy low end on hard panned guitars and raise the level on the S channel.

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

Post by Gold » Thu Aug 19, 2010 6:05 pm

I did the calculations for the potentiometer style attenuator. I even learned Reverse Polish Notaion to do it. Thanks iPAD! I ordered the resistors and did a mock up. The good news is that I basically got it right. The bad news is that even with .1% resistors the accuracy varies more than 0.2dB per step. Not good enough.

So off the switches go to Shallco to add a deck and make them bridged T. I haven't got the quote yet. I expect it to be painful. I was very happy that I was able to do the calculations and get it right. Baby steps.

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

Post by mediatechnology » Fri Aug 20, 2010 7:09 am

Gold wrote:I did the calculations for the potentiometer style attenuator. I even learned Reverse Polish Notaion to do it. Thanks iPAD! I ordered the resistors and did a mock up. The good news is that I basically got it right. The bad news is that even with .1% resistors the accuracy varies more than 0.2dB per step. Not good enough.

So off the switches go to Shallco to add a deck and make them bridged T. I haven't got the quote yet. I expect it to be painful. I was very happy that I was able to do the calculations and get it right. Baby steps.
Paul - You learned reverse Polish on an iPad? Wow. I'm glad to see RPN rediscovered on the iPad. RPN seems more "normal" doesn't it? You also need an HP35s. Fits better in a shirt pocket and the battery life is so long I've never changed one.

I don't know if you can make this topology work in your application but you might consider some form of gain trim that is not a potentiometric configuration. The resistor errors add along the string. IIRC In the mic preamp gain switches I built, I was able to keep the errors <<0.1 dB with 1% resistors by using a single resistor for each step. With 0.1% parts you should be able to do much better.

I haven't thought about it but how does a bridged T increase the accuracy?

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

Post by JR. » Fri Aug 20, 2010 11:39 am

RPN rulz

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

Post by mediatechnology » Fri Aug 20, 2010 11:45 am

+1 what JR. said.

The predecessor to the iPad was the hPad. Both trace their origins to garages.

http://www.amazon.com/Hewlett-Packard-F ... 654&sr=8-1

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