Nomical

DIY audio patchbay with digital routing....How hard?

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I need an audio patchbay and i was wondering how hard it would be to make the following:

I would like to have/make an audio patchbay (having a yet to be determined amount of ins/outs due to any diy building difficulties) that has the option of routing any input to any output digitally. No hardware switches or anything, just hook up all the ins and outs and patch everything through a menu. Ideally, this routing should be done on my Macbook Pro using a software mixer (similar to the Cuemix software of my MOTU) and something like a USB or FW connection. As this connection would be far more difficult to build I guess, routing everything on the machine itself using a display would also be sufficient. Each output should just have individual settings for which input is routed to it.

Outputs should also have the option of summoning/combining any number of the input signals to one single output. But the input should stay available to other outputs for making (sub)mixes on desired outputs. How is this summoning achieved? I guess they would all need an individual gain/level options or something to make sure that the summoned/combined signal doesn't overload the chosen output.

Making it even better is to have the option of selecting balanced/unbalanced signal on any individual in/out. My setup is a mixup of machines having balanced/unbalanced ins/outs and it would be nice to have the option of using a mixup of both of them when desired.

Thanks

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Not so hard:  in fact I'm vaguely working towards something similar.

1.  Choose an analog crosspoint matrix IC from Analog Devices.  Whichever one suits you for the number of ins, outs, etc. 

2.  Read all the documentation on that chip.

3.  Design a control surface & display.

4.  Design a PCB layout.

3.  Write a MIOS app to spit the right digital signals into the chip and respond to the control surface/display.

My impression is that the crosspoint matrix IC will handle multiple inputs to one output, one in to multiple outs, and any combinations thereof, whilst keeping levels nice.  I'd suggest a LED matrix as part of your display, with 1 LED for each crosspoint.  I have some other interface ideas I can show you if you like.

You could perhaps choose the largest IC you could imagine using (and afford) and just implement the pins you'll need in the first version, saving the rest for later expansion.

Have a look at the mod matrix on the SID control surface for a UI example.

the option of selecting balanced/unbalanced signal on any individual in/out.

I think this is just a case of having balancing transformers on each in and out, and using a switching plug - ie a 6.5mm stereo headphone-type socket where a stereo jack make a balanced connection and a mono jack makes an unbalanced connection - or one of those combination XLR-jack plugs, which have an XLR socket with a 6.5mm mono socket in the middle.  The XLR pins go to the balancing transformer and the 6.5mm socket pins bypass it.  Or just two separate sockets.  Whichever suits you better.

Once it's in the IC it won't matter that it's not balanced.

It might also be worth considering switchable +4db/-10db pads on the ins and outs.

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Now as a UI the patchbay idea posted here would be awesome ;D

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GHAH

AD8113

–14–

THEORY OF OPERATION

The AD8113 is a gain-of-two crosspoint array with 16 outputs,

each of which can be connected to any one of 16 inputs.

>:(

So much for that idea.  I'm going to keep hunting for a suitable IC or combination of ICs.  Sorry for the red herring.

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Found one:  using Chipdir and Octopart.

It's the Mitel MT8808 (PDF) 8 x 8 Analog Switch Array

Any combination of X and Y inputs/outputs can be interconnected

I've never heard of Mitel (/edit/ turns out they changed their name to Zarlink) before but at least this proves such things exist, or existed.

There are probably some other leads in these Chipdir categories:

Analog Switch

Mixer

Switch

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As per my wiki page "I will work on a digitally controlled analog switch matrix." I've been talking this up for some years now, with you too, DrB, I guess you forgot :) there's a 5 year old thread that didn't eventuate, and I am still waiting for someone to make the layout. Someone has already volunteered and it is on our list of projects to do. The chip to use is the AD8113. You can switch one-to-many with the chip, if you want to do many-to-one then you need a mixer not a switch array ;) You could always put a passive mixer after some of the outputs.

The trick is, that to get decent quality, you need to make it at least 2 layer PCB, up to 4. There are notes about this in the datasheet. In addition I have insisted that it be made in a way that will make it useful for many different people, not just one person - that means thinking about connections to chained boards for different architectures (16x32, 32x32, etc) and separate interface boards (balanced, unbalanced, etc), compatibility with existing apps, different CS boards and such. For a prime example of the right way to do it, see the mb-mixer board recently posted.

If you're interested in helping with this project (*cough*layout*cough*) please let me know ;D

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maybe i am mistaken but i can remember that somebody did something similar, a audio patchbay running over MIOS, can t really find, any idea?

Simone

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I'm happy to do a layout.

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:o

The only problem with matrix chips is that they have quite high crosstalk levels.

Relay matrix anyone?  ;D

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The problem with relay based matrices is that they are huge, and expensive.

TK:  :o What's THAT?! :D

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That's a DOCmatrix, duh :D

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The problem with relay based matrices is that they are huge, and expensive.

It's not that expensive when you get your relays on the surplus market (there's a store around here selling small signal relays for $0.50 ;D )

Otherwise I don't know if it would be easy to make reed relays out of reed switches to be sure to get something reliable... ($0.30 each + magnet wire)

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It's not that expensive when you get your relays on the surplus market (there's a store around here selling small signal relays for $0.50 ;D )

Otherwise I don't know if it would be easy to make reed relays out of reed switches to be sure to get something reliable... ($0.30 each + magnet wire)

Problem with surplus is that you end up with a design noone else can build. No good.

You could DIY the relays, but chances are the mass produced chip sold especially for the purpose will sound better, so that would defeat the purpose.

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How do you handle summing though if you use relays?  Wouldn't a transistor/op-amp based approach be better?

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Found another one: Analog Devices AD75019JP (PDF).  I don't know if it's a current production part, but octopart lists 5 stockists.

PRODUCT DESCRIPTION

The AD75019 contains 256 analog switches in a 16 ´ 16 array.

Any of the X or Y pins may serve as an input or output. Any or

all of the X terminals may be programmed to connect to any or

all of the Y terminals.

There's 10 9  ;D  available on ebay.au

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That's essentially the same as the 8113, but lacks the buffers (opamps).

Alas, it's been discontinued and replaced by the 8113, so it's not suitable as it will be harder and harder to find in future.

Edit: http://stromeko.synth.net/DIY.html#Matrix32x32

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So if you use this you have to make up your own buffers, and if you use the 8113 you have to somehow make up for

AD8113

16 outputs, each of which can be connected to any one of 16 inputs.

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So if you use this you have to make up your own buffers, and if you use the 8113 you have to somehow make up for

Yeh, and making your own buffers should be a snap. Although, if you want to use the 75019 with many-to-one, you still have to make sure it doesn't get overdriven somehow. I dunno how, hence needing someone else to do the layout :) ... And there's still the problem of availability. Although, I'd expect we could dig a few up... a bunch on ebay is good enough for us to get started (I'll buy the other 9 if it's workable) but it's not my aim to make it just for me.

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Maybe... Note that the stock availability is in the future... It's been that way every time I've checked it (regularly for years). Fancy emailing AD?

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Someone's got an eagle schem and needs someone else to do a layout?

[me=nILS Podewski]raises hand[/me]

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