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Old 20th April 2008, 07:19 PM   #1
NeoY2k is offline NeoY2k  France
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Join Date: Dec 2007
Default 8 channel 24/192 DAC: The transport question

Hello!

I plan to develop an 8 channel DAC using the Sabre Reference DAC.

The design of the DAC brings its own questions: but that's not the point here.

The point is: what transport to use for this device?

In 8 channel mode, the Sabre - if I understood correctly - needs to be fed by 4 i2s inputs. All right, what can we use beyond this points?

- 4 SPDIF/AES to i2s receivers. But we'll need 4 coax or 4 optical fiber! Very easy to implement. Remains the choice of the receiver: doesn't Wolfson makes an 8 channel version of it's receiver? (or is it a simple MUX at the input...).

- ADAT transmits 8 channels... But not at this sample rate. We would need to use SMUX 2 (96kHz) that transmits 4 channels per fiber or SMUX IV (192kHz) that transmits 2 channels per fiber.
I really can't see any advantage of ADAT SMUX IV over SPDIF, and using more or less fibers depending upon the sample rate, using uncommon devices for SMUX... Well, no, forget about it. DICE II from TC looks promising, but too much for me.

- Ethersound is a possible way to go, very promising, and I can get in contact with people from AuviTran and DigiGram. The point is, at this sample rate, we only transmit 4 channels on a Gigabit Lan. That's not enough, too sad.

- MADI may be possible: RME has the support for 8 24 bits 192kHz over MADI but there is no information available. It may be a quite closed standard, and very hard to get licenses - and the price may be mad too. Moreover, I don't want to spend the price of an RME HDSP Madi card!


Relying on common standards, I'll have to implement these 4 SPDIF/AES inputs on coax and optical, plus an ADAT that will only be used at 44-48 kHz.

But do you know any way to transmit these 8 high quality channels directly for a reasonnable cost?

Thank you very much,
Nicolas
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Old 20th April 2008, 08:48 PM   #2
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Where do you plan to get 8 channels from ?
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Old 20th April 2008, 09:49 PM   #3
NeoY2k is offline NeoY2k  France
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Join Date: Dec 2007
Hi,

The first thing is to connect all those outputs to a computer.

Adat would handle connection to digital mixing desks.
SPDIF would handle connection to anything that would output high quality digital audio, and may be used to connect to the computer - quite easy to make a USB board with 4 wolfson SPDIF receivers.

The point would be how to better connect it to a computer...

If I opt for a USB or FireWire controller stuff inside the box of the DAC, it would work. I just heard FireWire can now connect through CAT5/6 at up to 100m. May solve the problem. The funny part is now to develop drivers...

DICE from TC is a dream, it has all I need embededd in: AES, ADAT, FireWire with PHY driver over CAT5/6, and i2s,all that provided with a driver. But soldering 150+ BGA looks impossible to me, and 1500$ for the eval board is a bad joke.

What were you thinking about?

Thank you
Nicolas
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Old 21st April 2008, 05:17 AM   #4
phofman is offline phofman  Czech Republic
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How about a multichannel card with I2S signals on-board, e.g. any multichannel board with Envy24 chip? I2S does not like long runs, could be buffered by LVDS etc. - probably, details could be found somewhere on this site.
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Old 21st April 2008, 01:54 PM   #5
NeoY2k is offline NeoY2k  France
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Join Date: Dec 2007
Hey! Seems a really good idea, and if I'm right it can easily be interfaced in FireWire. Thank you very much

I ended up with the idea of doing this transport over FireWire. FireWire has the advantage of being able to directly connect to a PC, and run 100m over CAT5, at a rate of up to 400mB.

I could then also add a FireWire hub inside the DAC and add a "thru" plug: so I could connect several DAC/ADC racks in firewire and use the last to connect long distance over CAT5. Then the computer would directly receive and manage these signals

I looked at a lot of transport: HDMI is the most straightforward (directly outputs 8 i2s) but I have to develop an interface on the computer side, it doesn't run as long as FireWire can, cables are expensive... Even if chances are HDMI will be more used in studio than FireWire.
There's some intersting stuff in McASP from Texas too.

But I think: keep things simple, it is easy to add interface cards later.

All that stuff has a professional goal in mind - but for now, it is DIY that's why I'm asking myself questions about transports I would probably never use myself: as I'll build a handful of devices to sell to sound engineers, I have to meet their requirements.

To keep prices down I finally decided to have only 1 SPDIF/AES3 input (plugs are one of the most expensive parts....), when the DAC would be used in Stereo mode.
Then 1 adat for standard audio applications.
And 1 firewire for direct connect to PC and long distances applications.

Oh, there should be good beers by where you live

Thank you,
Nicolas
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Old 21st April 2008, 08:36 PM   #6
NeoY2k is offline NeoY2k  France
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Join Date: Dec 2007
Ok, after a full day of research, I'll end up with a DICE chip from TC.

These are a dream

Ok, the DICE II is not for me. But the Dice Jr should be manageable - the hardest part is in soldering a 122 pins package. I may love the evaluation board, but 1500$ is just too much for me.

So how do we do now with it?

Well, let's use the Dice Mini or Dice Jr.

It would then allow me connection on SPDIF, ADAT, Firewire, FireWire mLAN, and additional control if I like - maybe even a wordclock!

All that within the same chip

The question left is about FireWire networking and division of the bandwith when chaining or using hubs.

If it smartly manages the bandwith of each unit, that's cool! But if it divides blindly by 2 at each connected node... I might end up not that convinces.
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