Digital Patch Bay Suggestions

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Markd102

Markd102

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I'm after suggestions for a digital patch bay to use with a Digi001 system which has both S/PDIF and ADAT litepipe ins and outs at 24/48.
I've just purchased my second S/PDIF device (Presonus Digitube) and I want to be able to plug in both devices to the one S/PDIF input. 1 left chanel, 1 right chanel. I've been told in another thread that I need a digital patch bay, and I need some suggestions of brands and models.

I've been informed of the Fostex DP-8? (can't find it on their web site), and the M-Audio Digipatch (which is only 16bit in the litepipe section)

Thanks

Mark
 
I did quite a bit of research on digital patchbays a while back, and found out that *none* of them except the Z-sys Z8.8a will actually do >16bit lightpipe. Not the Fostex, not the Digipatch, *only* the Z-sys. All of them lie like dogs on their spec pages... except Fostex, who finally took any mention of ADAT _off_their page web page. So the Z-sys piece is the leading candidate these days, IMNSHO: http://www.z-sys.com/pp_detm.html#z8a

Steinberg also offers a unit that offers high-rate digital patchbay functionality for Nuendo: http://www.nuendo.com/starter.phtml?page=/hardware/dd8.html Don't know anything about the Nuendo piece, other than the fact that Steinberg never build anything themselves- so it is a rebadged product OEM'ed from someone else. I'd bet that it's a Rosendahl piece, by the look of that faceplate...

Bottom line, as I see it: you get what you pay for here. The ADAT interface is cranked right up to its limits with wide/high-rate data, due to the limitations of the extremely cheap TOSLINK hardware (the transmitter-reciever are being used right at the limits of their design specs). So you really can't just take the signal from a receiver, run it through a crosspoint switch, and send it out a transmitter, and still have decent clock stability and bit error rates. You need some hardware in there to regenerate the data, reync it with the clock you extract from it, and send it out the other end cleanly. The simpler switchers like the Fostex and Midiman products don't do that- and in the case of the Midiman, Bruce Valeriani discovered that his 24-bit data was actually being truncated to 16 bits on the way through the patchbay... Caveat emptor!

One other possibility: Hosa (yes, them!) makes a manual patchbay that is supposed to do lightpipe: http://www.hosatech.com/product_page_patchbay.html#PBP-362 . However, there's no real supporting evidence of that on their web page, and I'm not familiar with anyone who has ever had the guts to try these guys out- but there you go...
 
You might be better off with a digital mixer. There are several under $700. Since the routing in them is totally programmable you can plug everything in and route where you want it.

You'll spend more going this route but you will get a lot more for your money (mixer, control surface, more preamps, effects, and the digital patch bay.) Since you are using the DAC's on your Pre than you dont have to worry about their DAC properties so much. Just find one that has lightpipe and SPDIF in/out.
 
Ha! I just went thru this whole thing with digital PBs.....

I second Skippy's suggestion for the Z*sys Detangler......... it's really the only way to go.

The Fostex and M*Audio are limited to 16-bit - if they weren't, I know the M*Audio Digipatch would have been a good unit.

Now the Hosa... it actually DOES handle 24-bit, but here's the rub... due to the complexity of the LightPipe format, the digital signal is cloned - not simply transferred - from input to outputs. This introduces 2 issues - latency, and jitter.

On the M*Audio, both latency and jitter were unnoticeable to me, but I scrapped it 'cos of the word size. On the Hosa, latency isn't terribly noticeable, but the jitter on the clones is bad.... I wouldn't say unusable, but you can't set the bay up the way you would an analog patchbay.

The Z*Sys, as far as I have researched, is a much more stable and reliable unit - but it's 4 times the proce of the Hosa!

Bruce
 
If you were using ONLY S/PDIF (RCA) you can use an unbalanced analog patchbay. I have done it before and had no problems.
 
I felt a need to dispell the following comments. The point I want to make is that the digipatch does not recreate the adat signal it only redistributes it and to say that it won't transmitt at 24bit is absolutely incorrect. These boxes are formatt nuetral they don't care if they are listening to 2 channel or 8 channel adat they are only redistibuting what comes in to another location thus the definition for a patchbay.


>>>>I did quite a bit of research on digital patchbays a while back, and found out that *none* of them except the Z-sys Z8.8a will actually do >16bit lightpipe. Not the Fostex, not the Digipatch, *only* the Z-sys. All of them lie like dogs on their spec pages... except Fostex, who finally took any mention of ADAT _off_their page web page. So the Z-sys piece is the leading candidate these days, IMNSHO: http://www.z-sys.com/pp_detm.html#z8a

Steinberg also offers a unit that offers high-rate digital patchbay functionality for Nuendo: http://www.nuendo.com/starter.phtml...rdware/dd8.html Don't know anything about the Nuendo piece, other than the fact that Steinberg never build anything themselves- so it is a rebadged product OEM'ed from someone else. I'd bet that it's a Rosendahl piece, by the look of that faceplate...

Bottom line, as I see it: you get what you pay for here. The ADAT interface is cranked right up to its limits with wide/high-rate data, due to the limitations of the extremely cheap TOSLINK hardware (the transmitter-reciever are being used right at the limits of their design specs). So you really can't just take the signal from a receiver, run it through a crosspoint switch, and send it out a transmitter, and still have decent clock stability and bit error rates. You need some hardware in there to regenerate the data, reync it with the clock you extract from it, and send it out the other end cleanly. The simpler switchers like the Fostex and Midiman products don't do that- and in the case of the Midiman, Bruce Valeriani discovered that his 24-bit data was actually being truncated to 16 bits on the way through the patchbay... Caveat emptor!

One other possibility: Hosa (yes, them!) makes a manual patchbay that is supposed to do lightpipe: http://www.hosatech.com/product_pag...ay.html#PBP-362 . However, there's no real supporting evidence of that on their web page, and I'm not familiar with anyone who has ever had the guts to try these guys out- but there you go...>>>>
 
musicmovesme said:
I felt a need to dispell the following comments. The point I want to make is that the digipatch does not recreate the adat signal it only redistributes it and to say that it won't transmitt at 24bit is absolutely incorrect. These boxes are formatt nuetral they don't care if they are listening to 2 channel or 8 channel adat they are only redistibuting what comes in to another location thus the definition for a patchbay.
Click to expand...

Regrettably, your "clarification" is incorrect. We have been down this road before... Just to be sure, I just called Midiman tech support and reconfirmed with them: the Digipatch is a 16-bit only ADAT device. As Bruce Valeriani discovered (the hard way), if it is fed 24-bit ADAT data, it will truncate it (to 16 bits, in his case). Whether this occurs by design, or simply because of timing problems in the output data stream (due to the redistribution versus recreation isssue), data *is* lost in practice.

The boxes are only format-neutral for 16-bit ADAT. If you intend to work at greater bit depths, you will indeed incur truncation. And given that there are products that were designed to work properly at 24-bit, it makes sense to avoid the ones that do not.

If I'm incorrect in this assertion, then so is Bruce, and so is Midiman's own tech support group. If you call Midiman tech support, (626) 445-8495, and ask them the direct question: "I want to route 24-bit ADAT data through your Digipatch product, will it work?", then they will tell you "No, it will not work: the Digipatch supports 16 bit ADAT only".

It'd be interesting to have one on the bench and see if the truncation issue occurs only because of timing skews in the output data stream. It's quite possible that the device really does just shove the bit stream out the transmitter, but that the timing chacateristics are skewed to the point that the downstream reciever loses frame sync and drops bits- in which case, it might work for some combinations of gear, and not for others. Midiman tech support was not forthcoming with that information: they simply say that it doesn't support 24-bit ADAT.
 
digital patchbay

Let me go a little further about this situation. It may infact be a problem with the datastream coming down from the source via the lightpipe. However I'm still not certain this would apply if a master word clock device were involved(IE Lucid product). I'm still investigating this very fact. I know that at one point Midiman was not making the statement that it would not work with 24bit sources. I do have one of these units and have never had any issues with syncing of lock status with any of my units. I do have a lucid master clock involved and I'm wondering if that makes the difference???
 
Using a bit-test utility -- I have determined that routing a 20-bit ADAT signal THRU the M*Audio Digipatch DID result in truncation down to 16-bit...

If I took the Digipatch OUT of the chain, I saw a full 20-bits of info again...

Subsequent calls to Midiman's tech support CONFIRMED that the 12x6 only passes a 16-bit word size and does in fact truncate any words larger than that.

Why it does this was less of a concern to me than the fact that it DOES do it... period.

Bottom-line is that the Midiman DOESN'T pass 20 or 24-bits of digital info, and according to Midiman, there wasn't any plan to upgrade it do so either......

My "actual use" tests confirmed it, as did their own tech support... you can choose not to believe it if you like. Wouldn't be the first time someone at this site sees black when everyone else sees blue! ;)

Bruce
 
It'd be interesting to know. The funny thing is that sync-lock wasn't a problem for Bruce: the receiving equipment locked, and stayed locked. It just didn't see anything beyond 16 bits. He discovered this when the backup tapes he'd been creating were truncated, and he was a _seriously_ unhappy camper at that time.

A better master clock might have helped, but I suspect that it probably wouldn't. Is there any chance that you have a Hammerfall card? If so, could you fire up Digicheck and look at the actual recieved data stream, and see if you're getting any occasional bit errors down near the MSB (or perhaps no toggling at all)? I have a Hammerfall, but no Digipatch- and I don't feel like bringing one in just to rip apart on the bench...

I'd like to know more about this problem myself, even though my plans call for a Z-sys box some day soon. Fostex also used to advertise their bay as ADAT compatible, but had to remove that wording from their advertising materials when people complained about problems. I suspect that Midiman encourntered the same situation: a design that looked good on paper, but ran into problems in the real world. Anyway, getting concrete information on *why* this fails would be a service to everyone who comes to HR for information.

The fact is that the TOSLINK hardware is running right on the ragged edge of its designed-in speed capability at 24/48kHz. The receiver hardware was optimized for low cost, not high speed, and as a result you can expect timing errors to magnify in importance as you bump up against the limits. Like I said, I'd really like to know if this is actually a *framing* problem: the data is sent MSB-first, and timing problems in the receiver accumulate over the course of a data word until at some point the bitwise sync is lost. This will probably happen independent of the accuracy of the word clock itself, since it is an intra-frame bit-error problem (rather than an inter-frame problem that would result in loss of sync altogether, or popping/clicking).

The Z-sys guys get around this by implementing a complete receiver, properly regenerating and resyncing the bit stream, and then switching the cleaned-up stream to the output transmitter. And all that extra ironmongery costs money- you can see it in the price tag. However, I personally believe that because of the limitations of the TOSLINK hardware, that's the only viable way to make it work reliably.

If you can lay hands on a bitstream analysis program, and look in detail at the output of your Digipatch (especially switching from house clock to local clock!), it might help all of us understand the problem further. At the moment, all we really know is that it doesn't work reliably enough to be sold for that purpose... You may be suprised at the result- hopefully, happily surprised, in that you may have a setup that somehow works. I'd bet a beer that you're intermittently (or consistently!) losing some bits in there, though.
 
Digital patchbay

Well I just got off the phone with Randy at tech support for Midiman and we discussed this at great length. I'm running and have been running 24/44.1 for quite some time now flying tracks back and fourth to my computer etc...with not loss of lock/sync and no digital noise. Which as you know is the sympton of trying to pass 24 to 16 or vise versa. Randy at midiman suggested that it might be the 20bit data stream that was the problem not 24bit rates. The protocol which is known as dt-16 has been updated since it's introduction and may have allowed for passing 24bit but not 20bit adat. He did say that the intial info was about the digipatch not passing 24bit via the coaxial connections not the lightpipe. The lightpipe protocol does call for 24bit. He is double,double,double,double checking and will be sending me a full email explanation and I will certainly post here for more info.
 
Taken from the website:
"The Digital Audio Patchbay.
The Digipatch 12x6 is M Audio's response to the increasing need for interconnectivity between digital sources. In today's studio environment, more and more equipment utilizes S/PDIF, optical, or ADAT Litepipe, and the Digipatch 12x6 is ready to juggle all of these digital formats, streamlining your configurations and getting you right to making music.

Note: The Litepipe protocol used by the Digipatch, known as DT-16, is a format intended to support 16-bit Type I ADAT devices. Other Litepipe formats are not guaranteed to work reliably. All coaxial S/PDIF and Optical S/PDIF (TosLink) are fully supported."

I was tipped-off about the Type II ADAT incompatibility by posts on R.A.P. and after reading this blurb at their site, was prompted to look into it further....

The issue was confirmed when I examined my ADAT backup tapes and found they were all 16-bit (obviously truncated from their 20-bit versions)

I had to perform the backups all over again for at least 36 or so tapes...... I was NOT impressed........

Skippy knows -- I was bitchin pretty hard!

Bruce
 
Yup. Hey, Music: please do grab some bit analysis software and look at your own bit streams on the output of the Digipatch as soon as you can. There must be some software that will work with whatever interfaces you are using, and will let you confirm for yourself whether it is working as you expect or not. I'd believe your measurements much more than their tech support at this point- they are giving different stories to different people, sounds like.

As Bruce points out, his setup was also working quite seamlessly, except that he was getting truncated data- he only discovered it when he actually needed to _use_ his backup data. You may be getting some silent truncation too, and if that's the case you might want to change your working style a bit to acommodate it. It should be relatively simple to instrument and find out, and I'd surely like to know what you're actually getting.

I'm a bit surprised that we've gotten differing stories from their tech support, but only just a bit. I suspect that this issue may be a tad bit of a sore spot with them. But if it doesn't work with the 20-bit protocol, I have a very hard time believing that it is somehow _better_ with the 24-bit version.

Thanks for working this- whatever we find here will improve the breed...
 
skippy,

do you know where I could find that bit analysis software??? I don't. thanks I will check it out tonight and report back to everyone here.
 
It depends on your soundcard and its drivers- the software really should hook directly to the drivers. The only one I know directly is the one suppled by RME for my Hammerfall soundcard- that is a wonderful tools for this sort of analysis and debug work, but ut us Hammerfall-specific. There are others, I'm sure. Bruce, what did you use? Anybody else have any pointers?

The first thing to do would be to check the web site for the manufacturer of your sound card. Your recording software may also have hooks in it for this kind of analysis. Without knowing what you have, I can't really make much in the way of a recommendation...
 
It was using the Digicheck s/w from the Hammerfall card.............

Bruce
 
Yeah I have a frontier design Montana and Dakota card. I've contacted them to see if they have a utility that would help. In the mean time I did find this box that says it supports 24/96 and is almost a 1/3 of the cost of the Z systems unit. I see the Macmidimusic.com offers it Check it out.

http://www.friend-chip.de/dmx8.htm
 
Yeah, I've looked into that unit. The web page for it is completely uninformative. They say they support 24/96, but what do they *mean*? ADAT itself doesn't support 96kHz, so do they mean that they only support it on the S/PDIF ins, or only on the coaxial S/PDIF ins, or what? I'd be a lot happier with it if they specified that it supported ADAT Type II right there, but they do not. That worries me.

Even on the page that describes their MOP4 module (for their lager modular routers) says "ADAT up to 50 kHz", and doesn't specify which of the protocols. That might mean 16 bit only, or 20 bit only, in addition to the 24 bit that they support elsewhere. It's painful trying to read poorly written specs. If it can do Type II, then they should just flat *say so*- otherwise, we all have to assume that they really can't, just like the other guys.

A search of the Usenet archives shows a certain level of interest in this among the RAP folks, but no actual operational experience with the unit. I'd proceed with extreme caution on that: there are now 3 manufacturers who have claimed to support 24/48 Type II ADAT, and have had to back away from those claims in practice. These guys may indeed be able to do it- but I'm skeptical...

I put in a call to a guy at MacMidiMusic, and he's going to check out that issue directly with the manufacturer and get back to me. It is cheaper than the Z-sys, but I'd rather buy right and pay the freight than buy twice!
 
Yeah I hear you. I'm quite skeptical at this point. How hard is it to print what your product can do and move on. The digipatch unit was completely mis represented because I asked specifically about the 24bit application. I knew that was exactly what I would be using. I'll be looking into the z systems myself if the other unit doesn't pan out. I just wish I could find someone other than sweetwater who was carrying them so I wouldn't have to pay full retail. I want to make this purchase once and once only like you.
 
The Hosa unit DOES pass 20-bit ADAT... BUT - I'm finding jitter is an issue....

I'm going to sell it off as soon as I can find a suitable alternative.........

Bruce
 
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