SPDIF / ADAT data transmission rate?

J

Jan

New member
I have to make myself a cable of about 10ft long in order to connect a 8channel 24bit breakout box to my RME DIGI96PST soundcard.

I’m wondering if I will have to use special data transmission cable like 75ohm Ethernet coax cable or if I could also use a good quality shielded audio cable.

Does anybody know something about the data rates that are transmitted over a SPDIF, or in this case ADAT format data cable?

Does it come close to the 10MBs that is send over a 10BaseT Ethernet connection?

Thanks,

Jan
 
If you want to connect 8 channels at a time, ADAT is the only way to go as SPDIF is only 2 channel.

For ADAT you will need an optical connection. It will take much longer to find separate connectors and cable then to order a made-up cable (probably cheaper as well). Standard lenghts: 1.5m 3m 5m (10m). If you are in a hurry, go to a hifi shop and use a toslink cable.

SPDIF has 2 common cables: optical and coax. For optical the cable is identical to ADAT. The coax connection is 75ohm cable with RCA/cinch connectors. Ethernet cable is 50ohms, so better not use it. Video cable is ideal and cheap. Good quality audio cable can be used if short (lets say <1m) but don't blame me if you're unlucky. Better do the inverse and use good quality 75ohms cable for your audio.

As for datarate:
SPDIF: 2.8224 Mbps@44.1kHz
ADAT: don't know the exact frame structure, but something around 10Mbps@44100kHz

BTW: 10baseT is only 10Mbit/s
 
Thanks for your suggestions. It is a rather peculiar case since I will have to connect a computer extension card with a ADAT signal over a normal wire and not optical. Inside the computer the converter card is connected to my RME DIGI9624PST with a very short shielded cable of only 20cm. I more or less extended this to one meter to get the converter card out of the computer case, closer to my patch panel.

I build an external power supply using 7805 and 7812 voltage regulators so that should completely eliminate any computer interference.

I will first try it with a standard 9 pin computer cable of about 1,5meter, because I also need to extend the clock signal. If that should not work I will use video cable like you suggested, I am thinking of something like SCART cable because it has more wires and should all be separately shielded.
 
Can you tell me what type of cable is used inside the pc? Do you have a connector pinout? This may help to determine the best type of cable and how to use it.
 
I hope that you understand that what you want to do will void your warranty!! You can try it, but please understand that by doing so, you may damage your cards (both of them) and then it will cost you more than a separate adat convertor. Even if you don't break anything, there is no garantee it will work and/or keep working.

The interface drivers on the cards are no "real" drivers. It are probably just IC output ports. This means they are not made to drive any lenght of cable. They can keep up with the 20 cm, but 10 ft is something different. Problem is the capacitance of the cable. This may over-stress your drivers leading to failure.

Also is the clock signal going by a different cable. Inserting a longer cable may upset the timing of the link.

Third, by putting your a/d convertors on a seperate psu, you introduce the possibility of an earth loop. So instead of less noise, you will have a big humm.

If you want to try anyway, do so at your own risk, don't hold me responsible. You may get away by using cat5 network cable. It has the bandwitdh, reasonable capacitance and is cheap and easy to find. Use one pair for the data, and combine two other pairs for the clock lines. Here you have two possibilities: 1, take one wire of each pair as ground and use the other for a signal; 2, use one pair for the signals and take a complete pair for the ground.

Good luck, but you are taking a risk.
 
I’m willing to take the risk. I already build the power supply and that works great. If the card’s outputs won’t manage I will build an extra buffer.

I’ll try you twisted pair cable. I’ve still got a nice piece of special shielded twisted pair that could do fine.

I’ll keep you informed,

Jan
 
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