Syncing multiple devices to master clock source

[crichton]

I could use some help trying to solve clock setup issues when connecting several devices to my audio interface. The manuals are of no help at all, I can't seem to able to turn up any good documentation elsewhere, and -- as you will be able to tell -- I am somewhat confused about the issue altogether.

I have an Alesis Mastcontrol audio interface, which has 3 digital inputs, 2 ADAT and one S/PDIF. I'm connecting an ART Voice Channel and a Focusrite 8-channel preamp to the two optical ADAT inputs and a Boss pedalboard to the coaxial S/PDIF. I'm using a Mac, running 10.6 with Logic 9.

From the available options in the Audio/Midi preferences I assume the clock source cannot be set for each individual input but there's just one global clock, thus I must decide on one source for all devices. Trouble is I can't seem to figure out how I can set the clock in a way that would allow all 3 devices to be in sync.

The Mastercontrol has no Word Clock input or thru, so any syncing through BNC is not an option. However, from what I understand, ADAT has two-way clock syncing built in, so I could set the Masterverb's clock to "Internal" and both devices to "External Wordclock mode" Is that correct or am I way off with this assumption?

If I can sync up the ADAT devices that way, what about the pedalboard which is connected via S/PDIF? If I were to set the Masterverbs clock to the clock of the pedalboard, would the ADAT devices automatically slave to that?

Any ideas on how I could get this working would be very much appreciated.

 

[oretez]

without possibility of 'distribution' (for example 'word clock' from a central source typically over BNC connections) your only option is to use the thing everthing else connects to as the master, and every other device slaves to it.

Even attempting to daisy chain two ADAT devices in your scenario would be problematic

in addition to somewhat more standardized 'Word Clock' there is a specific ADAT sync carried via a nine pin serial connection. If any of your devices have that you daisy chain and in most cases the 'master' clock will be passed to both (or more devices)

How obnoxious lack of a central clock will be depends on a lot of variables . . . ranging from nearly unnoticable to entirely unusable, depending not only on synchronization issues but how clock protocols are implemented in firm and/or soft ware.

unfortunately in the scenario you describe you have to settle for 'the' clock you can pass to each device, the master by default, rather then what might be the best or most stable clock on a different device

 

[oretez]

If I can sync up the ADAT devices that way, what about the pedalboard which is connected via S/PDIF? If I were to set the Masterverbs clock to the clock of the pedalboard, would the ADAT devices automatically slave to that?

.

no. While daisy chaining is possible and unattractive artifacts derived from it are variable, so called sync-lock is dependent on a physical connection between master and slave (sort of). Attempting to slave a second slave (i.e. daisy chaining) to the slaved clock can produce unwanted artifacts . . . ranging from negligible to unusable. But as a general rule in a daisy chain scenario you will not be sample accurately sync'd to the master clock

 

[crichton]

How obnoxious lack of a central clock will be depends on a lot of variables . . . ranging from nearly unnoticable to entirely unusable, depending not only on synchronization issues but how clock protocols are implemented in firm and/or soft ware.

Thanks a lot for the reply.

Unfortunately I already found out where I'm at on the spectrum of "obnoxiousness" when no central clock is used -- pretty much at "entirely unusable". When I set the clock to the Masterverb's internal one, I get a loud high-pitched pop every 3-5 seconds. The other sources are even worse. I guess that leaves me stuck, angrily shaking my fist at what seems to me like a pretty cumbersome technological standard.

 

[oretez]

I'm not sure 'obnoxious' is exactly the correct sentiment

'clock' (as buzz word) is an essential component of digital audio (and not just digital, and not merely audio data in digital realm) . . . whether as analog pressure wave or digital data stream time is an inseperable variable for any audio representation

In a lot of ways digital audio is still relatively new in terms of evolution. And development has been rapid. Less then thirty years from 8 bit 22 kHz 5 sec samples to virtually unlimited number and length recordings @ 24b 96 kHz. The development has been fueled, in part, by lots and lots of competing companies trying to get the next 'big thing' packaged in a way that a sufficient number of consumers would perceive it as the next big thing. Lots of things died by the side of the road, some, momentarily, became 'industry standards'

Synchronizing any two independent digital streams requires that one acknowledge and deal with variations of the independent 'clocks' of the devices. This is inevitable due to what digital audio is and how it is implemented via hardware. Approaches to synchronizing multiple data streams can be purely proprietary. I.E. one can only sync gear from a single manufacturer or they can attempt to permit sync'ng a broad spectrum of different manufacturers gear. ADAT sync is proprietary. So called 'word clock' is a loose standard that can be applied across a number of hardware platforms. But even then it is implemented by manufacturers in different ways with varying degrees of success. An, also, inevitable circumstance of the chaotic development of digital gear.

Trying to synchronize two pieces of digital hardware is not particularly difficult . . . for rather obvious reasons. And in consumer devices these interconnects are pretty seemless but don't tend to permit any user modification. Throw a third devise into the mix and you start running into problems.

Word clock distribution is purely a way dealing with the problems.

Off the top of my head I could not even tell you how many A/D/A converters I have but for past decade a serious issue in selecting which to purchase has remained 'how well will it connect with other digital gear'. I have some stuff that is ADAT only. One 2 channel converter on the general purpose desk top computer that syncs via s/pdif only. But by and large if a device does not support word clock distribution it has to have some very serious muscle in other areas or it is just not worth the hassle. To me. I record both live shows and studio sessions. While I maintain a project room/studio at least half the sessions are tracked at some other location. I tend not to know, in advance what gear is going to be available, tend to have only a general idea of what gear a client will need. While I've refined, perhaps made more efficient, work process over the years to reduce confusion, etc. fact remains that modular systems remain an integral part of 'rig' strategy.

Being able to rapidly reconfigure, scale, appropriately sized rigs has always been a marketing tool . . . having digital gear that can be combined seamlessly is a necessity. I at times get frustrated by competing protocols and sloppy, marketing driven implementation . . . but I've been at this a long time and started with a band that when we actually got our own mics had ones with Tuchel connections, phone hi-z connections, XLR mics that required phantom, Back Electret condensers with XLR (or phone or phono connections) that might run on a battery, XLR dynamics that did not require phantom, & at least one ribbon that was fried by a tech plugging it into (XLR) a board channel on which phantom power was engaged (Still have SM57 variants with tuchel & Hi-Z phone plugs, they're old but they still work)

point? Yeah!, frustrating as hell when stuff does not connect the way you want it to (and no matter what the in love with analog boys want to believe intermodulation among daisy chained valve gear could, at times, be as not pretty as any digital aliasing) but these problems arise only because the scope of what we can do has increased and cost has decreased dramatically . . . on the balance not a bad bargin