DIY PC audio interface

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Looks like fun......

Well, I'm not sure how much help I could be but a few years ago I spent the better part of a year doing an ASIC design in VHDL. It mostly dealt with Rambus, AGP and Bridge PC stuff. I'd be rusty having not touched dig design in 4 years but I still have my code and testbenches for the AGP, Rambus and Bridge interface stuff which is not distant from PCI, I could try to refresh my memory

For all I know I'd be completely useless in this project but I have been kind of looking for something to get me back into dig design, I miss it......

I have no idea how much time I could lend or how quickly I could ramp back up to being even remotely quick with VHDL but it sounds like fun. Work kind of gets crazy come the first of the year as wel......

Unfortunately I no longer have access to the ModelSim environment I used then, I have been playing with some software Ive found online for kicks but I'll dig around.

Let me know if I could help.... I'll see what I can brainstorm.

Brian
 
Just thinking about interface ideas

You FPGA folks know a lot more about these things - but i just want to throw an idea into the pot.

Which would be easier to connect to the outside world - separate I2S pins, or a TDM'd interfaces (so 1 PCI card could connect to *loads* of converters?)

for simplicity, single I2S streams would fit the bill, but I'd really like to be able to do TDM's of 8 channels at a time.

Whats the next step here - agree a specification? Agree on a team? Anyone tackled a similar project before?

cheers

R
 
Throw me some links to some of the formats/specifications the design would be dealing with. A block diagram with i/o for each block would be helpful. I'll better read through the posts and see if I can get a better overall picture.

It's bed time....
Brian
 
hmmm...

I've put an idea down diagramatically. In no way would i think this final, or even beginning to be detailed enough. It's always good to have somewhere to start from.

overview1.gif


I figure that this kind of layout allows the system to be as flexible as possible, so it can accomodate adat, s/pdif, tdif or whatever interface you want to hook into it. You just change the "interface card" (maybe a plugin card onto the FPGA card?)

Early days yet - I want to understand how many channels are possible etc.
Any specialists in this stuff that can advise - it's time to speak up! :wink:
 
FPGA is by far the most robust option...

We need to find someone who is familiar with windows ASIO drivers. If we can make a PCI card with a spartan on it, and the opencores PCI bridge, and write ASIO drivers that can quickly transfer data to and from the FPGA, the rest becomes very very simple.

Then we just implement MADI or whatever other format we want in the FPGA, add whatever termination or other glue circuitry is necessary, and then build a nice rackmount box with another FPGA in it which is stuffed full of A/Ds and spits out MADI. That box can be a 64 channel line in A/D, have mic preamps in it, whatever we want.
 
Hmmm... Obviously, we need the input of an FPGA expert and someone who knows their way around ASIO drivers.

One of the reasons I was interested in the firewire chips is that they come with ASIO drivers already written. *sigh*

ANyone with background in drivers for windows and mac, please speak up!
 
I'll start looking into MADI, and try to write a wishbone to MADI bridge... at that point I'll just need to talk to the driver writer and implement 'hooks' in the hardware that the driver can call to do whatever magic it needs to do :) A lot of that will depend on how the ASIO architecture works, which I'm really not familiar with.

We can go ahead and design and prototype the A/D + MADI box if we wanted to... would be easier if we had an existing MADI interface card - anyone wanna buy me an HDSP-MADI? :D For this box, we need to settle on an A/D chip. I've had my eye on the AK5394:

http://www.asahi-kasei.co.jp/akm/en/product/ak5394a/ak5394a.html

very impressive specs on that toy. I'd LOVE to see a selectable rate 48/96/192 converter box. I know we could do 64x48 or 32x96 over MADI, I dont have any confirmation one way or the other whether we could do 16x192. I don't think there's any good reason to do multiple rates at one time, say 8 channels of 192 combined with 16 96k. IF MADI supports it, which I dunno that it does, I don't think most DAWs will let you record multiple sample rates at once.
 
oh holy crap, those AKM parts are expensive.

The 5394 isn't even priced online yet, and they're only available in 1000 counts.

The 5393 (24/96, 118dB s/n) is $27 apiece, and you have to order in 100 counts. And here I was with grand visions of stuffing 16 of those in a box for a nice 32 channel interface. Not when the A/Ds will cost $400! :(

Rochey, any suggestions on some good clean easy to work with TI A/Ds that wont cost us a mint? Can you get us an employee discount on a tray of 'em? :D
 
there's another thread here about gutting a Behringer ADA8000 box and replacing the frontend and possibly the converters.

I'm going to put on my salesguy hat on now.....

PCM4204 - 4 Channel 118dB 196KHz ADC. - A _very_ funky little device :grin:

PCM4104 - 4 Channel 118dB 192KHz DAC - The 'brother' part.

Both devices can do a TDM interface that allows 2 devices to chained together. So streaming this straight out of the interface might be a handy thing :D

PCM4204 is $15 in 1K quantities. Obviously, none of us are working on that volume. If you need 4 of them (for 16 in box) then you can use digikey, or alternatively try and use the sample program.
PCM4104 is about $7.50 in 1K. Again, try digikey or the sample program.

Anyway, that conversation is happening in the other thread. I think they are aiming for an ADAT output. Although I have suggested that an S/PDIF output would be nice. That would make it convertable into almost anything.

I'm having a look a the windows driver page on microshite. I've never been so scared in my life.

Please... we need someone brave (and who has some idea what he's doing!)
 
looks nice... is there a 2 channel part in a dual package (rather than the quad flatpack) with similar specs?

when I'm looking at wiring up a chip on a piece of perf with wire wrap wire, low pin count is a Good Thing :)
 
If you are going to do all of this work maybe jumping in at PCIe would be a good thing. Boards with x16 PCIe video are in the market and Intel seems to want PCIe. PCI might go away like ISA. It seems the push is for high speed serial that can be added together like PCIe
 
maybe first we can try adc/dac + fpga which output firewire, ethernet... see how hard and how much time it takes, and then try to make a MADI pci (or PCIe) card?
 
agreed...

I'm just looking at something even simpler to start off with -- a 4 channel USB ADC card to record things on location. (I do some recording at gigs and churches)

So far, I'm looking at the TAS1020B and the PCM4204.

Tell me what you think.

Cheers

R

EDIT: It looks like the maximum throughput on the TAS1020 is 4xMono Streams of 24bits at 48KHz... but then, at 118dB... that's quite acceptable :cool:
 

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