HD IO - 16 Analog Inputs plus SPDIF inputs

[ZerglingPhilosophy]

Hi. I bought an HD IO in 8x8 configuration with no digital card. I used all 8 input channels and used the stereo pair SPDIF input as well simultaneously.

I just purchased an AD expansion card to go to 16x8. The problem I have now is that the Hardware Setup window for the HD I/O only has rows up to 15-16. Since I am trying to run 16 channels of analog input, that leaves no room for the enclosed SPDIF [encl].

Is this a limitation of the HD IO that I did not realize? I did not figure the 2 SPDIF inputs would replace the ability to use 2 analog inputs.

[JFreak]

It is working as designed. DigiLink cable passes 16x16 channels of audio, with a possibility to relay another set of daisy-chained 16x16 for a total of 32x32 per card connector. But one box cannot use the channels of the daisy-chain, which means you need to choose which 16x16 you wish to use.

[JFreak]

Avid interface boxes are "only" 16 i/o but you can use that expansion port to daisy-chain like this: second box primary port goes to first box expansion port and the cable needs to be as short as possible.

Some 3rd party boxes such as Apogee Symphony II does the daisy-chaining internally. That box has space for two maximum of 16x16 i/O cards but the HD option card only has single DigiLink connector. The box feeds channels 1-16 from first i/o card and channels 17-32 from second i/o card, but it is still 100% meeting the spec.

You cannot daisy-chain more than two boxes into one card connector, because trhe cable maximum is 32 channels.

[ZerglingPhilosophy]

OK, so does that mean there are max 64 channels of input per a single HD Native or HDX card? 16 + 16 daisy-chained for connector 1, and 16 + 16 daisy-chained for connector 2. Sounds like I'd have to pick up an empty HD I/O and daisy-chain if I wanted to run SPDIF in parallel.

[Darryl Ramm]

Originally Posted by ZerglingPhilosophy

OK, so does that mean there are max 64 channels of input per a single HD Native or HDX card? 16 + 16 daisy-chained for connector 1, and 16 + 16 daisy-chained for connector 2. Sounds like I'd have to pick up an empty HD I/O and daisy-chain if I wanted to run SPDIF in parallel.

There is very clearly a limit of 64 IO on HD Native, as stated *everywhere* in the product specs and documentation.

Not sure what you mean by "in parallel".

Hardware Setup lets map the chassis digital I/O into the 16x16 I/O, possibly replacing other I/O ports if it's a full system. All described in the Pro Tools and hardware documentation.

Every Digilink cable connection is 32x32. it's a fundamental limitation of the Digilink (aka TDM2) protocol on the connection. The Avid HD IO boxes max out as 16x16 to let you have two boxes on a single Digilink chain. And they offer the ability to configure the internal cards and chassis IO to fit within that 16x16 HD IO box limit.

Other Digilink boxes use the full 32x32 IO of a single Digilink connection (and therefore you can't chain off those boxes).

All other limits, HD Native card max IO, number of IO on a HDX/HDX2/HDX3 etc. come from these limitations.

I hope you are doing all this for a good reason. It's pretty hard to justify spending money on Digilink hardware with HD Native vs just going 3rd party modern ASIO/CoreAudio interfaces. HD Native cards are less then a year away from end of support (whatever that will mean... but likely not good).

[ZerglingPhilosophy]

Great info, thanks. I went HDX for extreme low latency tracking and because I did not want to deal with non-AVID cue mixing software. I added to my HD IO because it seemed to be the path of least resistance to expand my channel count from 8 to 16. Since I want Pro Tools integrated low latency, that puts me at a MTRX Studio, which are backordered forever, a lot more cost than just adding 8 channels to my HD IO. I like the idea of an ASIO interface but value keeping everything in Pro Tools. I am not going to go to a second HD IO just for SPDIF, it'll be a causality at this point.

[JFreak]

Okay, cool. So in short, the Avid box gives you 16x16 i/o and the flexibility to choose which physical connectors you route to the DigiLink cable. Darryl pointed out you get precise info by RTFM

[Darryl Ramm]

Originally Posted by ZerglingPhilosophy

Great info, thanks. I went HDX for extreme low latency tracking and because I did not want to deal with non-AVID cue mixing software. I added to my HD IO because it seemed to be the path of least resistance to expand my channel count from 8 to 16. Since I want Pro Tools integrated low latency, that puts me at a MTRX Studio, which are backordered forever, a lot more cost than just adding 8 channels to my HD IO. I like the idea of an ASIO interface but value keeping everything in Pro Tools. I am not going to go to a second HD IO just for SPDIF, it'll be a causality at this point.

OK gotcha I misunderstood you were running off HD Native cards.

You can find 192 IO with Digital cards used at very good prices (~$350)... that's what I would do if I was sure I did not likely to need more HD I/O analog I/O in the near future as well. As more people get off HD Native I expect the prices of used HD IO will also decrease. Unlike the analog inputs and outputs, the 192 AES/EBU and S/PDIF will be as good as on a HD I/O (but be aware none of the internal boards are not compatible). Both 192 IO and HD IO offer sample rate conversion on the digital boards but not the digital chassis I/O. ... for me (who likes to be able to bring in 48kHz AES/EBU into 96 kHz sessions that always made the enclosure connections fairly useless. But now I use RME outboard boxes that do sample rate conversion in them).