SPDIF and ADAT I/O Question.

Hello OffAnAirplane,

Under normal circumstances, your guess is right. The digital input should provide you with 2 additional tracks(left/right) from your line-level source. However, make sure you check the user manual of your intended unit first to see if the analog inputs are not deactivated while there's an incoming digital source at the same time.

ORIGINAL: ohhey

ORIGINAL: OffAnAirplane

Ok, as mentioned in another thread I am considering either purchasing a MOTU 896HD or a Presonus FireStudio (when they arrive) for using as a live on-stage mixer. I will be able to control the mix with the software mixer, and also it will give me the ability to multi-track record our concerts. My only concern is that it will only give me 8 channels, which would be plenty, but if I have a playback device like a CD-player it will take up two of those inputs. But the 896HD and the FireStudio both have Digital I/O, and the Mini-disc player I use now (Tascam MD-350) has Digital I/O also, with a Toslink connector. I am very unfamiliar with the format of digital I/O and what can and cannot be done with it. So my question is, could I take the Toslink digital output from my Mini-disc player into the Toslink digital input on the 896HD and play it that way, leaving all my analog inputs still free?

It could be done with a converter like the M-Audio CO2. That's not the problem. The problem is that the CD Player won't have a clock input so it will have to be the master clock (not good). And, because you are using a digital interface the entire project will have to be 44.1 and maybe 16bit also.

I talked to the fine folks at Sweetwater today and asked one of their techs this same question. And they told me that though they are both optical Toslink style connections, the MOTU is AES/EBU, and the Tascam player is SPDIF. And you would have to convert it before it would be compatible. I actually own an M-Audio CO2, but I think it only converts coaxial SPDIF to optical SPDIF, and doesn't convert to AES/EBU at all. I'm actually looking at it right now, and that is how it appears to be. Hosa does actually make a device that will convert this though.
This device:
http://www.sweetwater.com/store/detail/CDL313/


I still need to check on what sonic said, about the possiblity of it disabling the analog I/O when using the Digital. I'm not sure about that.
I wonder if the clock source will be a problem, like you said. That might be the main reason I can't do this.

I might just be forced to buy a Presonus Firestudio instead. It actually has SPDIF I/O, unlike the 896HD.

ORIGINAL: Sorceress Sarah

My MOTU 828mkII has optical connectors which are configurable as ADAT or TOSlink. Problem solved.

Hmm. You mean AES/EBU or SPDIF? Cause Toslink is just the connector type.

ORIGINAL: Sorceress Sarah

ORIGINAL: OffAnAirplane

ORIGINAL: Sorceress Sarah

My MOTU 828mkII has optical connectors which are configurable as ADAT or TOSlink. Problem solved.

Hmm. You mean AES/EBU or SPDIF? Cause Toslink is just the connector type.

No, I meant exactly what I said.

ADAT is 4 stereo channels, TOSlink is a single stereo channel. The data formats are different. When you bring up the "MOTU FireWire Audio Console", a piece of software used to configure the MOTU driver, the 828mkII tab has two drop-downs. One specifies the format of the optical in, the other specifies the format of the optical out. You can select ADAT or TOSlink. Either way, you use a TOSlink optical connector.

I use the optical connectors on the 828mkII in ADAT format. I connect them to a Roland DIF-AT24 which converts Roland's proprietary RBUS format to ADAT optical, and passes the digital output of the Roland XV-5080 to the 828mkII and the clock from the 828mkII to the XV-5080 to sync them.

In your case, you could take the TOSlink out from your disk player and put it to the Optical in on the 828mkII configured to use TOSlink. You're done. Here's the snag. . . Unless that disc player has a way to get an optical signal back to it, you might have a problem with sync. Unless you use the disk player's clock as master. . . (I wouldn't). Investigate how to sync the two pieces of gear together first.

My Minidisc player has an optical input as well as an output. I don't know if it can get it's clock source from an external source or not. I guess it could. Also, do you know if the 896HD can also function this way, if it's optical inputs can be selected to be Toslink?

ORIGINAL: OffAnAirplane

I have actually decided to get rid of my minidisc player and get a Tascam CD-01U Pro for playback. And it actually has an XLR AES-EBU output, and the 896HD has an XLR AES-EBU input, so I think that will work perfectly.

Thanks for the help.

I don't know about the 896HD's optical ports. My 896 (not HD) does ADAT only, The 828mkII does ADAT and TOSlink.

You still may have a clock issue with the CD-01U. You have to get everyone on the same page of music somehow. . .

ORIGINAL: OffAnAirplane

ORIGINAL: Sorceress Sarah
You still may have a clock issue with the CD-01U. You have to get everyone on the same page of music somehow. . .

How is that normally done?

I'm not familiar with that piece of gear so I couldn't tell you. But you say that the Minidisc player has an optical in. If it's capable of using an external clock, that's where you squirt it in.

ORIGINAL: OffAnAirplane

ORIGINAL: Sorceress Sarah

ORIGINAL: OffAnAirplane

ORIGINAL: Sorceress Sarah
You still may have a clock issue with the CD-01U. You have to get everyone on the same page of music somehow. . .

How is that normally done?

I'm not familiar with that piece of gear so I couldn't tell you. But you say that the Minidisc player has an optical in. If it's capable of using an external clock, that's where you squirt it in.

Well, actually I'm going to get rid of the Minidisc player, and I just bought a Tascam CD-01U Cd player. It has an XLR AES-EBU output, which is what I was planning on using to connect to the 896HD's XLR AES-EBU input. And there is no optical input on this CD player, just an output.

Well let's think about it for a minute. . . AES-EBU is a digital format that requires a 110-ohm XLR connector to transmit data one way. . . From output to input. Data is embedded in the clock. . . So. . . you have no way of getting the clock into this CD-01 device. . .

You could try it, and it might be fine, but you might have problems. . . Hard to say intil you hook it up. Good luck on that. . . Let me know how it turns out.

ORIGINAL: OffAnAirplane

I talked to MOTU about it, and they said that the AES/EBU cable can trasmit the audio and the clock signal simultaneously. So I need to set the clock source in the 896HD to AES/EBU. And set the clock source in the CD player (if it is a changeable setting) to internal. And that should do it.

Yes, and you will be limited to 44.1 and the quality of the clock in your CD player

ORIGINAL: OffAnAirplane

ORIGINAL: ohhey

ORIGINAL: OffAnAirplane

I talked to MOTU about it, and they said that the AES/EBU cable can trasmit the audio and the clock signal simultaneously. So I need to set the clock source in the 896HD to AES/EBU. And set the clock source in the CD player (if it is a changeable setting) to internal. And that should do it.

Yes, and you will be limited to 44.1 and the quality of the clock in your CD player

I record at 44.1 anyway. And would you think the quality of the clock in the CD player wouldn't be as good as in the Motu? I have no idea. It's a pretty nice CD player as they go. Tascam CD-01U Pro

Yeah... you may not notice any difference, I hope the clock stays on all the time on the CD player even when it's not playing.

ORIGINAL: Sorceress Sarah

I've been making a study of clocks and their effects on digital audio. This is freaky-geeky stuff. Way to many maths. Let it suffice to say that at 16/44.1 a clock with less than 20nanoseconds rms jitter should suffice. Outside of that and you'll have issues where the 896HD will mistake data for the clock and vice-versa. And you'll blame MOTU. Not their problem. The clock is EVERYTHING in digital audio. Use the best clock you can possibly use.

This stuff gets into the uber-geeky when you want to actually use that 192kHz sample rate and higher bit depths. Clock stability in the femotseconds range is required for adcs and dacs and even AES-EBU stuff to work right.

I've never even seen a media player that can accept an external clock source. I figured if anyone would have one, Tascam would. Maybe not. That may be the best way to do it, but it is not an option, that I can tell.

Which brings up a stupid question. . .

If you record at 44.1 kHz, why did you sepend the big bucks for the 896HD? Just curious. . .

Because that is the only 8-channel interface with 8 good mic preamps, with 8 seperate phantom power switches, a DSP mixer, a firewire interface, and enough outputs to do what I need. The only other options that I am aware of (that I would consider) are the Presonus FireStudio (which hasn't been released yet) and the Mackie Onyx mixer (which is not very compact, and I wanted compact.) Maybe RME or Lynx make versions that do this as well, I have no idea, but I'm sure they are much more expensive. And I've used an 896HD before, so I know I like the sound of the converters and preamps.

I mean I could just use two of the analog inputs for my CD player and make this much more simple. But I've only got 8 analog inputs, and that will use up two of them, leaving me with six, which might not be enough. True, I could go ahead and buy an 8-Pre which would give me 16 inputs, and then I would'nt miss those two as badly. And that is probably what I'll do, especially if I have synchronization issues between my CD-player and the 896HD.

I'm trying to do something somewhat unique here, and I'm having to learn as I go. Although, when I talked to Motu, they acted as though lots of people use the 896HD as a live mixer. So who knows.

ORIGINAL: Sorceress Sarah
Fair enough. . . I just think you could have saved some money by buying the older 896 model, not HD. You paid a premium for the ability to handle the 192kHz clock, but you're not going to use it. . .

Now, there may be some hope for you here if you want to use higher bit rates in that the MOTU should be able to handle sample rate conversion on the AES-EBU input. IOW you can run the CD at 44.1 kHz, trigger off of it's clock and upsample to 48, 96 or maybe even the 192. . .

Higher sample rate is not the only difference between the 896 and the 896HD. I read somewhere that the 896 only lets you mix to output 1 and 2 in it's cuemix, whereas the HD will let you mix to any of it's outputs. And there was something else too, though I can't remember what. But I bought this used on eBay anyway, so I didn't pay premium. I just about never buy this sort of thing new, anymore.

BUT!!! your success with this will largely be dependent on how good the clock in the Tascam player is. . .

All of this leads me to speculate about what would happen in an environment where there were two of those Tascam CD players and a device with multiple AES-EBU inputs. . . Whose clock would you go by? But that's another topic. . .

I don't know. You would think, since the Cd player is just an audio source and not an interface, it would have an option for getting it's clock signal from an external source. But I guess not.


Edit:
Found that thread which told about the 896 vs. 896HD here. About the 6th post from the top.

ORIGINAL: ohhey

ORIGINAL: OffAnAirplane

....
I don't know. You would think, since the Cd player is just an audio source and not an interface, you would think it would have an option for getting it's clock signal from an external source. But I guess not.

That would be nice but would open up another set of problems, for example what do you do when a customer sends a 96k clock signal (or anything other then 44.1) to the CD player ?

This is the problem with digital interfaces it's not easy or reliable, even the cables can cause problems you just don't have with analog interfaces. It's not just the clock, all those digital audio interfaces are non error checking, not only do you have errors because it's a serial (single direction) interface there is not even a way to tell when you have errors or how bad it is untill you hear them and most are not audible. That not so much a problem with CD playback but for recording it's something to avoid if you can. I'm not saying they are unusable because it's no where near as bad as the old DAT machines but it's something to consider. If you can keep your system down to one digital device that is the best way to go.

More than one digital device is doable if you've got a stable clock. I'm getting a real education on this stuff lately. I'm discovering that there are not a lot of clock sources out there that are even adequate for 16/44, much less the higher bit rates/depths.

And here's a puzzle. . . Since these manufacturers like MOTU et al, know that the clocks that are available are not up to snuff, they build in a circuit called a clock recovery circuit. It, too is a digital circuit. Which means that by definition, it's least significant bit is uncertain. So. . . It now becomes possible to feed a clock signal to the unit that is so stable that the clock recovery circuit becomes a source of jitter. . . Mind-bending stuff. . .