Linked Tascam DR-680s: Theory vs. Practice

[saxplayerscott]

I have read everything I could find on Gearslutz about the Tascam DR-680 eight track recorder. There are a few discussions of using the Sound Devices USBpre 2 into one of the recorders to get the last two of the eight channels. (Without an external source connected by spdif, these recorders effectively have six channels.)

I have bought two of the recorders, which can be linked together by a sidif cable to garner 12 channels. That will most likely be enough for what I want to do.

However, I believe it should be theoretically possible to connect the spidf out of recorder A to the spidf in of recorder B to link the recorders AND connect a an external stereo pre like the Sound Devices USBpre2 to the spdif in of recorder A to produce a total of 14 possible channels.

Plus, of course, take advantage of the better quality pres in the USBpre 2.

I say theoretically possible because there are some threads on here where people seem to have had difficulty getting an external pre to work on the spdif in of one recorder. And I have found nothing about anyone trying to link two of these recorders and spdif an external pre into one of them.

If it is doable without major headaches, I might throw down for a USBpre 2, which I could use for some other purposes as well. But if it is going to major headache, I will just live with the 12 channels and the pres in the Tascam unit.

Anyone tried this?

[Foldedpath]

This is just "theorycraft" and not personal experience (I have one DR-680, not two), but I can't find anything in the manual that indicates that this wouldn't work. That's assuming you can get a good SPDIF recording on tracks 7-8 of the master unit, when used alone.

In Cascade mode, the SPDIF connection between the two recorders only sends transport control commands, no clock info which might complicate things. The master DR-680 should sync its clock to the incoming SPDIF data stream, and the second DR-680 will just be in free-running mode. You'll still have to deal with whatever small timing variations might exist between the two recorders. See the release notes on the Tascam site for the latest v 1.20 update, which has some tips on improving sync.

The additional two digital tracks aside... I'm very curious to know how well the two recorders sync up in that Cascade mode. I don't think anyone here has posted a test yet (unless I missed it). So please post your results, whether or not you try adding the UsbPre2. I've been thinking about picking up a second DR-680, mainly for parallel backup of live recordings, and not in Cascade mode, for safety. But it would be nice to have the option of expanding to 12 or 14 tracks when I'm recording multiple takes and don't need a parallel backup.

(Edit to add By "sync up in Cascade mode" I meant how much clock drift there is for a long recording, whether both recorders initialize the file at the same moment, how much later editing is needed to line up the files, etc.

[saxplayerscott]

Yikes! I am glad you posted that. I assumed that the second unit would use the clock of the first when they were hooked together, and that they would be in perfect sync.

I just got the units last week. I think at this point I will return one of them, use the money to buy the Sound Designs USB2 Pre, and try to figure out a way to live with 8 channels.

My whole idea is based on simplicity. I want to be able to do a quick level check, turn the recorder on at the start of a set -- 45 minutes to an hour -- and split the tracks up later.

Frankly, worrying about drift is not something I want to think about.

Scott

[MichaelPatrick]

Originally Posted by Foldedpath

... By "sync up in Cascade mode" I meant how much clock drift there is for a long recording, whether both recorders initialize the file at the same moment, how much later editing is needed to line up the files, etc.

If thy lock in sync there won't be any drift. Align the tracks in your DAW just once and you're good to go.

[philper]

Are you sure that you cannot clock the two DR680s together via SPDIF from recorder A to recorder B? To have this not be possible, and to have the 2nd recorder free-running with respect to the first isn't logical, and doesn't sound like the way Tascam usually does things.

phil p

[Foldedpath]

Quoting here from the Tascam release notes for the 1.20 firmware update:

"A cascade connection only controls the transports of the units simultaneously. Word clock is not synchronized. As a result, the clocks of the master and slave units are not synchronized and discrepancies could occur in the recordings made on the two units."

The document in that link above has some tips for "improving" sync, but it's still not actual word clock sync as far as I can tell. Also the manual doesn't mention it, but obviously it would be smart to use the exact same brand and model of flashcard for both recorders when operating in this mode.

Since this is targeted more towards the film/video crowd anyway, I think the ability to run in Cascade mode is just for adding a few tracks if you need it on the fly, with short recordings where the sync might be good enough. It's not designed as a long-form concert recorder in that mode. Going for full sync and modular expansion would probably have killed their target price point, for a feature that not that many people would use.

[philper]

Originally Posted by Foldedpath

Quoting here from the Tascam release notes for the 1.20 firmware update:



The document in that link above has some tips for "improving" sync, but it's still not actual word clock sync as far as I can tell. Also the manual doesn't mention it, but obviously it would be smart to use the exact same brand and model of flashcard for both recorders when operating in this mode.

Since this is targeted more towards the film/video crowd anyway, I think the ability to run in Cascade mode is just for adding a few tracks if you need it on the fly, with short recordings where the sync might be good enough. It's not designed as a long-form concert recorder in that mode. Going for full sync and modular expansion would probably have killed their target price point, for a feature that not that many people would use.

Having the same card would not change or help anything. The guts of those cards come from a small number of suppliers no matter what the brand is.

Any additional tracks added to a film/video recording rig need to be in dead frame accurate sync to avoid A: serious sync issues in post and B: the recordist being fired. In video we don't do "good enough" sync for dialog.

Wouldn't sending an SPDIF output of any mix or input from recorder A to the SPDIF input of recorder B cause the 2nd recorder to be locked to the clock of the first? (Not using cascade mode.) I would rather have to start the machines separately and have them locked together than have transport control of B by A and no synchronization at all. Has anyone tried this?

phil p

[Foldedpath]

Originally Posted by philper

Wouldn't sending an SPDIF output of any mix or input from recorder A to the SPDIF input of recorder B cause the 2nd recorder to be locked to the clock of the first? (Not using cascade mode.)

One would think so, but the documentation is confusing. I just sent a question about this to Tascam, using their web tech help form. If I get a response, I'll post it here.

An end-user test would be great, but all the reviews I've read are for single units.

[MichaelPatrick]

Originally Posted by philper

Wouldn't sending an SPDIF output of any mix or input from recorder A to the SPDIF input of recorder B cause the 2nd recorder to be locked to the clock of the first? (Not using cascade mode.) I would rather have to start the machines separately and have them locked together than have transport control of B by A and no synchronization at all. Has anyone tried this?

Tascam shot themselves in the foot on this one. The manual says:

When using the cascade function, the digital output jack of the MASTER and the digital input of the SLAVE are used for the cascade function, so they cannot be used for digital signal input and output.

I'm with you Phil. Enable clock sync and turn Cascade OFF. Run the transports manually!

[saxplayerscott]

Finally got to test out my Tascam DR-680s.


I got back into town, took a glance at the manual, upgraded the firmware that was on the recorders as I got them (from 1.1 to 1.2), and got them hooked together with the sync cable.


As suggested in the notes with the 1.2 firmware, I routed the stereo out of the Master recorder to channels 7 & 8 of the Slave recorder by changing the input selection for channels 7&8 on the slave to DIN. (Tascam claims this will help reduce drift.)



I connected two stereo mics to channels 1 & 2 of each recorder, started a metronome going and recorded it for an hour. I pulled a channel from each recorder into Audacity. I could detect no audible or visual drift, even after an hour.



So I think the two hooked together are likely going to work fine for my purposes. I am planning to try to stop and restart the recorders after every song if I can remember to do it in the heat of playing my gig. At the most they might go 15 minutes or so. Just for grins, I may split the snare drum to both recorders to start, let the things run for a while, and check those tracks against each other.



I have a SD USBpre2 on the way. If I can can get that connected to the spdif in of the Master recorder and still sync the two together successfully, I will have a possible 14 channels. If not, I will either go with one recorder and eight or two with the sync cable for 12.



And since I am not getting paid to record -- but paid to play -- it's not going to be the end of the world if something goes south once in a while. What I am after is a way to record my gigs with an eye toward making a live CD by collecting the best stuff over a period of a few months.



So far, the recorders seem pretty easy to figure out.



I will be curious to see if I can squeeze out 14 channels with the pre. But even if I can't, there will be times when I can get by with one recorder and 8 channels using the pre. And like I said, I can use it for other things as well.



The nice thing about starting out trying to record my regular Tuesday night gig is that the venue and players will be held constant. I can change one thing at a time, listen to the results, factor in the ease of setup and replication, and figure out the practical solution that yields the best results.



Thanks for all of the advice and counsel. I will keep you posted after I actually try to record a gig.



Scott

[Foldedpath]

Scott, thanks for that report. That's what we needed; a hands-on test.

Just to be clear: were you doing the 1 hour test with Cascade mode enabled, using recorder #1 to start and stop #2?

[philper]

If there is really no drift at all over an hour....I'd try a 4 hour test! If there is still no drift then the machines are clocked together no matter what they say (Tascam customer support has often been wrong about the deeper aspects of their equipment over the years, I was often telling them things they didn't know about the HDP2). There's no other way they could stay in sample-accurate lock for that long otherwise. In any case this is good news.

phil p

[saxplayerscott]

Yeah, the two recorders were cascaded together, with one stopping and starting the other. The slave recorder had the channels 7&8 set to DIN, which takes the stereo mix from the master recorder and drops it on those tracks. I am not sure what the technical reasons are, by the Tascam update notes say this may help prevent drift.

I had a differnt stereo mic, a Shure VP88 and a Chinese knockoff of a Shoeps connected to inputs 1&2. I looked at channel 1 from the Master and channel 2 from the slave. The wave forms looked a bit different (different mics, different positions to the source). But I could detect no lag or drift either by listening (which is what I reallly care about) or by
sight.

I bought a mic splitter for my live rig. Tonight I may take a single mic and split it to both recorders and perform the test again, letting it run for several hours. That is way beyond what I will need, but it will be interesting to see. And the wav form should look pretty much exactly the same, I would think.

I had the same brand and type SD cards in both recorders, Class 10 16g cards. Not sure if that matters. But I figured it would not hurt. They were plugged into the same power source.

Scott

[Antti P]

Thank you Scott, this is great info.

A bit off topic, but do solos work like it was one recorder? Havent found it in the manual.

Antti

[saxplayerscott]

Not sure about the soloing of tracks on the slave recorder. I will check that. I set the levels and all that stuff with them seperate. Then I enabled the master/slave thing and hit record.

[MichaelPatrick]

Originally Posted by saxplayerscott

Not sure about the soloing of tracks on the slave recorder. I will check that. I set the levels and all that stuff with them seperate. Then I enabled the master/slave thing and hit record.

If the Cascade option sends clock data the solution may be ideal. I look forward to hearing more about this if it works!

[kritter]

I have a tascam DR-680 and have a mate with another, this is great news..! Thanks for the updates Scott

[saxplayerscott]

Well, never one to leave well enough alone, I performed another sync test on the two recorders linked together with a spdif cable.

Once again, all the Tascam literature, website updates, etc., make it very clear that the slave recorder does not use the word clock of the the master. In the cascade mode, the master recorder start/stop, etc, control the slave recorder. That's what Tascam says.

Last night I cascaded the recorders as before. Following the Tascam advice in one of their updates on reducing the chance of drift of two cascaded recorders, I turned the DIN function on on the slave, routing the stereo output of the master to tracks 7&8 on the slave.

I put a beta 57 on one or the speakers of my digital keyboard, spilt the output through a Pro Co mic splitter and sent it to channel 1 on each recorder, and turned on the keyboard's metronome.

I hit record at 11:30 p.m. and went to bed. I turned the recorders off at 8:30 a.m.

The Tascam manual says that the recorder will start a new file everytime the file size reaches 2 gigs. What seemed to happen was that once the stereo file hit 2.15 gigs, a new take was started -- new mono files and new stereo files on each recorder. Over the course of 9 hours, it did that 5 times.

I just pulled the last take from each recorder into Audacity. The files sound and look perfectly lined up after 9 hours.

I don't know (or really care) how all of this works from a technical standpoint. But it does appear to work.

I just bought a SD USB2pre. My next experiment will involve hooking that up to the Master, trying to get the recorders Cascaded with the pre hooked up, and running another sync test to see of they still stay in alignment. That would give me 14 channels.

But before that, I will be trying the recorders out on a gig, using all 12 channels.

14 would be nice, but I can for sure live with 12. . .

Scott

[philper]

Originally Posted by saxplayerscott

Well, never one to leave well enough alone, I performed another sync test on the two recorders linked together with a spdif cable.

Once again, all the Tascam literature, website updates, etc., make it very clear that the slave recorder does not use the word clock of the the master. In the cascade mode, the master recorder start/stop, etc, control the slave recorder. That's what Tascam says.

Last night I cascaded the recorders as before. Following the Tascam advice in one of their updates on reducing the chance of drift of two cascaded recorders, I turned the DIN function on on the slave, routing the stereo output of the master to tracks 7&8 on the slave.

I put a beta 57 on one or the speakers of my digital keyboard, spilt the output through a Pro Co mic splitter and sent it to channel 1 on each recorder, and turned on the keyboard's metronome.

I hit record at 11:30 p.m. and went to bed. I turned the recorders off at 8:30 a.m.

The Tascam manual says that the recorder will start a new file everytime the file size reaches 2 gigs. What seemed to happen was that once the stereo file hit 2.15 gigs, a new take was started -- new mono files and new stereo files on each recorder. Over the course of 9 hours, it did that 5 times.

I just pulled the last take from each recorder into Audacity. The files sound and look perfectly lined up after 9 hours.

I don't know (or really care) how all of this works from a technical standpoint. But it does appear to work.

I just bought a SD USB2pre. My next experiment will involve hooking that up to the Master, trying to get the recorders Cascaded with the pre hooked up, and running another sync test to see of they still stay in alignment. That would give me 14 channels.

But before that, I will be trying the recorders out on a gig, using all 12 channels.

14 would be nice, but I can for sure live with 12. . .

Scott

This is great news. As to how they stay in sync, well, you were either very lucky, or there is some other sort of signal that they two sets of ADCs are using to stay in sync with each other. The clocks in sub-$1000 recorders and interfaces like a DR680 are not very accurate in general, and even professional gear with very accurate temperature compensated crystal clocks will drift off a jam after 8 hours unless they are cabled together, so TASCAM must have found some other scary science method. Good on them.
So--another test for you: if they really don't use any clock or sync etc connection then they should stay in dead sync even if there is NO connection between them, right? I'd appreciate it if you could give this a try sometime, and let us know what happened.

phil p

[MichaelPatrick]

Originally Posted by philper

they should stay in dead sync even if there is NO connection between them. I'd appreciate it if you could give this a try sometime, and let us know what happened.

I agree! That would be a useful experiment.

[Bgreen]

I've done this a few times with two and three DR-680's to cover side or late night stages where we didn't feel like putting in a full set up. I've never had any issues at all with drifting. Works like a charm.

[philper]

Originally Posted by Bgreen

I've done this a few times with two and three DR-680's to cover side or late night stages where we didn't feel like putting in a full set up. I've never had any issues at all with drifting. Works like a charm.

I'm glad it worked for that gig but that isn't really a test of the machines being in dead sync if the tracks were looking at different instruments-lots of room for slop there. The only way to really know would be to record a tone or voice and maybe TC with no connection (or their cascade thing). In any case this all makes this recorder much more useful than I had thought.

phil p

[saxplayerscott]

I wonder if it has something to do with the fact that I am sending the stereo out of the master to channels 7&8 of slave, via the DIN setting on the slave. Who knows. I guess I could try that other test sometime. Would be interesting to see.

Since I only plan on recording for 10 to 15 minutes at a time, I am not going to get too worked up about it. If it had failed a reasonable test (which I would consider to be my first one hour test), I probably would have returned the second recorder and tried to make my thing work with 8 tracks.

I am going to get them out on my gig next Tuesday and use all 12 channels.

Scott

[philper]

Tascam says they don't send WC between the machines, but maybe they send some other sort of signal that keeps them in sync....? Tascam is so funny--this is actually a really great feature but they don't make much of a deal about it or explain it very well.

phil p

[Foldedpath]

A follow-up on that question I sent to Tascam support, about whether using a SPDIF connection from recorder #1 to recorder #1 without being in Cascade mode, would sync in any way. The answer from Tascam:

"No, have to be in the cascade mode for the S/PDIF to the second unit to work."

That was it... no expanded answer on sync options. So, SPDIF to the second recorder only works in Cascade, and it seems to be some kind of proprietary data mode so they can embed the transport functions.

[philper]

Originally Posted by Foldedpath

A follow-up on that question I sent to Tascam support, about whether using a SPDIF connection from recorder #1 to recorder #1 without being in Cascade mode, would sync in any way. The answer from Tascam:



That was it... no expanded answer on sync options. So, SPDIF to the second recorder only works in Cascade, and it seems to be some kind of proprietary data mode so they can embed the transport functions.

I think that's the answer: they are locked via SPDIF. Cool.

phil p

[saxplayerscott]

Well, that's more than I got from Tascam technical support. I asked them if I could spdif an external stereo pre into the first one AND cascade the recorders together to get 14 channels total.

No response after a couple of weeks. I'll just try it and see if it works.
If it doesn't, it's no big deal. I can get by fine with 12.

I was mostly interested in whether I could get a better pre on two of them.

[philper]

Originally Posted by saxplayerscott

Well, that's more than I got from Tascam technical support. I asked them if I could spdif an external stereo pre into the first one AND cascade the recorders together to get 14 channels total.

No response after a couple of weeks. I'll just try it and see if it works.
If it doesn't, it's no big deal. I can get by fine with 12.

I was mostly interested in whether I could get a better pre on two of them.

Well that response or lack of one is pretty much been my experience w/ Tascam support in recent years. There always seems to be a gap between what the engineers in Japan who design the gear know and what TASCAM USA knows. I will tell you that in over 30 years of using TASCAM gear the only really solid info I ever got was from the Japanese guys there--we got so we would keep calling until we got to one of them.

phil p

[saxplayerscott]

For what it's worth. . .

I finally heard back from Tascam technical support on the issue of whether two linked DR-680s can take an external pre to the master recorder. The short answer is "yes." I guess I will find out, as I found a lightly used SD USBpre II and should have it in the next couple of days.

If that does work, my channel count would go to 14, which would give me a couple spares for when I have extra players/singers on hand. And I will have two channels on a better quality pre (which I plan to use for the main stereo mic or my sax and vocals).

To me, there response contradicts their one of their updates on improving sync. That update said that sending the stereo out of the Master to tracks 7&8 by changing the slave setting for those tracks to DIN helps the sync. I am no techie, but if I am doing the above, and "the cascade does not pass audio from the master to the slave, only transport control commands," as this guy from Tascam says in the e-mail below, how does the stereo out from the Master get from to tracks 7&8?

I've given up worrying about this. If it works, it works, if it doesn't, it doesn't I'll give it a go when I get the pre. Here is what Tascam said:

Thank you for contacting TASCAM.
Our customer support representative, ADurrant, has written
the following response to your message:

Scott,

The cascade function only synchronizes the transport controls. The input settings, internal mixer settings, record functions, take and folder operations are still controlled separately.

When using the cascade function, the digital output jack of the master and the digital input of the slave are used for the cascade function, so they cannot be used for digital signal input and output. The cascade does not pass audio from the master to the slave, only transport control commands.

You may still use the digital input of the master unit to record audio to 5-6 or the stereo track. Each recorder will record six channels of input and a stereo track. The only limitation is the digital input of the slave unit cannot be used to record audio because it is being used for cascade control.

Thank you for your interest in TASCAM products

[supo]

How does the sound of the DR680 compare to the HDP2 two-track recorder? I have an Oade Brothers Modified Version - sounds great. Was wondering if the stock or Busmann 680s sound as good or better than the HDP2 (stock or Oade for those who may have it).