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 »

My vote is for:
Soft bypass
Separate utility board for full hard bypass (optional).
Simple mute switch for M and S
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mediatechnology
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Re: Mid Side M-S Matrix Uses No Precision Resistors

Post by mediatechnology »

OK, that gets us down to one DPDT relay.

This thing almost has to come up to a patchbay anyway so you can get to the M-S process inserts.

I'd still put extra tie points to bridge C and F (4 points total).
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mediatechnology
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Re: Mid Side M-S Matrix Uses No Precision Resistors

Post by mediatechnology »

Three relays sounds better than nine.

Edited:

I think we'll have to explain why there are two bypass options but having half hardware does eliminate a lot of cascaded stages when the M-S gizmo is not being used.
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Re: Mid Side M-S Matrix Uses No Precision Resistors

Post by Gold »

I hesitate to throw this in but since it seems to getting pimped out... The obvious missing piece is gain/pan between the M and S. Impedance wise I don't think passive attenuation would work anywhere in the circuit (correct me if I'm wrong) but would be fine with me. Level adjustment would be much more useful than the solo options IMO.
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mediatechnology
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Re: Mid Side M-S Matrix Uses No Precision Resistors

Post by mediatechnology »

Paul - That added bit is here:

http://www.picocompressorforum.com/foru ... p?f=6&t=71

I was thinkin' that might be another board/module just to keep the complexity of the pure matrix down. It's based on Rick Chenn's '94 design but using 1240s and a Graeme-style (Jerrald) polarity flipper.

Switched attenuators can work and can be used to widen up the center range of the control so it doesn't go hard mono or hard difference too rotationally fast. In the width control, bypass is also required to keep high separation when panned halfway between Mid and Side for unadulterated "stereo."

One of the problems doing width is that the gain changes considerably with mono (mid) having an up to 6 dB build-up and difference (side) being considerably less on most material. (On mono it is of course zero output.) SSL used a third pot on their control. I should scan that one.

I'd prefer to keep the matrix simple. Once gain trim is introduced the ability to have high seperation is blown. It would seem that whatever is in the process loop is going to allow gain trim anyway. If solo isn't really needed just eliminate it. I'd prefer it to just be the balanced I/O, encoder/decoder and soft bypass. With those it's going to have 12X THAT ICs. 4X 1246/1206, 4X 1240, 4X 1646 and one DPDT relay. Other than bypass caps (and optional sense caps for the 1646s) there are no passive components in this thing. None.
Gold
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Re: Mid Side M-S Matrix Uses No Precision Resistors

Post by Gold »

I guess I shouldn't have used the word pan in my post. I was thinking of an opamp loss/gain stage at point F in your drawing with a separate control for M and S. A pot would present too high a source impedance to the decode stage, correct? It could be jumpered out if not needed. Would that degrade performance beyond having an extra opamp?
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Re: Mid Side M-S Matrix Uses No Precision Resistors

Post by emrr »

The multiple solo options seem bitchin', but inclined to agree with Paul and suggest simple mutes in each path. Gain at point 'F' could be useful, especially given how many external processors will not have gain knobs of their own. But 'F' gain seems like a minor point to me; I have other methods if necessary.

I would personally use this as an external piece to patch when and where needed, so 'C' to 'F' bypass works for me. Quick soft bypass of the entire matrix circuit here is pulling the final return cables out of the patchbay, which would be equivalent to Roger's Pico soft bypass, I believe. Or pull all 4 patchbay cables for hard bypass.
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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 »

OK.

Paul - I think gain trim could be introduced at F before the bypass relay. The trim would only affect only the external processor return for both the M and S channels individually and, when bypassed, would not reduce E-E separation. Using this control it's possible to "null out" the unknown gain error resulting from the termination at D. The question then becomes: "How much trim range?" It would require an op amp stage one each for M and S.

Doug - I'm likin' the KISS principle here on the first ones which seems to follow your suggestions. Option A: Mutes (switches perhaps), extra M and S PCB tie points, single bypass from C to F with a DPDT relay and no gain trim. Or, option B, add the return gain trims to option A.

Should the mutes be at C or F? (D or E require more contacts.)

If Roger's up for it we could panelize 3-4 of these, pay him for them, build them as prototypes and be beta-testers.

Would option A or A+B be a good starting point?
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Re: Mid Side M-S Matrix Uses No Precision Resistors

Post by Gold »

I would find the gain trims useful. In a mastering rig there aren't usually spare line amps laying around. +/- 6dB would be plenty for me. +/- 3dB is actually all I could see using but others might find that limiting.

Edit: I'm certainly willing to pay Roger for his time and beta test.
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Re: Mid Side M-S Matrix Uses No Precision Resistors

Post by emrr »

mediatechnology wrote:Doug - I'm likin' the KISS principle here on the first ones which seems to follow your suggestions. Option A: Mutes (switches perhaps), extra M and S PCB tie points, single bypass from C to F with a DPDT relay and no gain trim. Or, option B, add the return gain trims to option A.

Should the mutes be at C or F? (D or E require more contacts.)
I'm thinking at F, though C would allow you to hear noise floor/errors/etc of processing with no source signal. Paul may have a strong argument for C.
mediatechnology wrote:If Roger's up for it we could panelize 3-4 of these, pay him for them, build them as prototypes and be beta-testers.
sure
mediatechnology wrote:Would option A or A+B be a good starting point?
A+B I think; could always hardwire around the gain option.
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Doug Williams
Electromagnetic Radiation Recorders
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