S/PDIF Sync Risk and Workflow

    Hi,


    Being a life long analog studio guy I still struggle on occasion with niche digital situations. The KPA has just introduced a new one due to it's S/PDIF limitations. Yes I could run analog out, but I'd rather not if possible. So here's the question....


    Right now I have my system set up to run S/PDIF out of the KPA. But when I'm not recording with it I turn it off and my DAW interface (a Fireface) is smart enough to auto-switch back over to it's internal clock. The DAW software is none the wiser, it will sync to whatever the Fireface is currently syncing to. Anybody know if I am risking some kind of sync/alignment issue with the guitar tracks vs. the rest of the session with this kind of approach?


    Thanks,


    Sonic

    Hi,


    The sync you refer relates to the clocking of digital data as it moves through connected devices.


    Given that you're not recording anything from the KPA you will have no issues as sync is not important as no data is moving.


    You will not encounter any issues with time alignment.


    I haven't looked at the manual but ideally you should (if possible) set the KPA as a word click slave and have your interface as master. Then you can just leave everything as is. If not you still won't have any issues in your use case.


    Regards,


    Simon

    Right, KPA is master - but that's only when it is ON. When it is off, the Fireface becomes Master again. This is why I'm wondering what the implications are. Two different masters contributing tracks to the same project.

    Exactly.


    As long as you don't switch clock sources midstream, you'll be fine. The clock signal is part of the stream, so by definition, if you turn the Kemper off, streaming stops, and so does the clock signal; the Fireface would then take over, as you said.


    If you're recording a track, whether the stream originates from the Fireface or Kemper via the Fireface, it'll be viable as long as you don't switch the Kemper off during the process.

    Quote from SonicExporer

    Right, KPA is master - but that's only when it is ON. When it is off, the Fireface becomes Master again. This is why I'm wondering what the implications are. Two different masters contributing tracks to the same project.

    it'll work as long as you make sure that the Profiler becomes the sync master for your fireface once you switch the amp on.

    Get in touch with Profiler online support team here

    Being as I am always listening through the analogue outs on the Kemper when creating a sound, I don't see the point of using a limited S/PDIF. Often sessions come in with higher sample rates to the studio and won't work anyway.


    If the analogue outputs are what you normally listen to when happy with a sound, there is probably a slight difference in tone when no conversion takes place.

    Karl


    Kemper Rack OS 9.0.5 - Mac OS X 12.6.7

    Quote from grappagreen

    I think we all agree that irrespective of slave/master capability as long as the KPA is master and interface slave when moving audio there is no impact.


    Si

    Agreed but having to sync to the KPA all the time, requiring it be powered on always, is not a viable work flow solution. Nor is having to remember to manually tweak clock settings. So as long as you have an interface that is intelligent enough to know what to sync to then it becomes workable, as long as there won't be any alignment issues as a result, which it sound like not.

    On this topic, since I'm just learning about all this stuff myself.


    I have a Focusrite 6i6 interface, and unfortunately that one doesn't seem to be able to automatically switch sync source.


    To have it working with my PC, while the Kemper is off, I have to set the sync source on the 6i6 to "Internal" - otherwise no sound can be heard at all (not just from SPDIF in/outs).
    So that's my default setting....


    When I want to record something over SPDIF with the Kemper, I have to remember to switch the 6i6 sync source to "SPDIF".
    If I do that while the Kemper is already on, the Focusrite will say that it's locked - but then I seem to be getting sync/crackle issues.
    If I only turn on the Kemper after changing the setting on thr 6i6, then it seems to be working.


    Can this really be the case? Seems like one, or both, of the units have a somewhat fragile/fiddly implementation of SPDIF. Is should surely be possible to sync up correctly, regardless of what is turned on when???

    Quote from Kasper_Fauerby

    When I want to record something over SPDIF with the Kemper, I have to remember to switch the 6i6 sync source to "SPDIF".
    If I do that while the Kemper is already on, the Focusrite will say that it's locked - but then I seem to be getting sync/crackle issues.
    If I only turn on the Kemper after changing the setting on thr 6i6, then it seems to be working.

    It should work regardless of order - can you double check if this is "systematic"?


    Otherwise, I'd contact focusrite support. I don't think the Kemper is the problem in this case. I wonder if the interface doesn't actually switch, although the software seems to indicate that it does.

    Quote from Kasper_Fauerby

    Can this really be the case?

    The Focusrite sync source will automatically lock, once it is in use.
    In use means e.g. your DAW is already running or any other video or audio playback (or recording) software makes use of the interface. It doesn't necessarily mean a playback is currently running. Just any active software that might use the audio interface is enough.


    If you prefer to get rid of this whole topic of syncing the interface and still want to use the Kemper via S/PDIF, your best option is to get an asynchronous sample rate converter like the Behringer Ultramatch PRO SRC 2496.


    Personally I don't mind to remember switching the Sync Source anymore. Just got used to it. Although I have to confess that I really don't like the fact of "Kemper must be Master" along with its restriction to 44.1kHz sample rate.


    As a general remark ... the existance of S/PDIF adds so many GREAT options for proper recording, I don't want to miss it. Reamping via S/PDIF is a breeze, no troubles with noisy inputs on the Kemper backside. Also you can use all the outputs for many different signals. Record the Master Stereo signal via S/PDIF, add Git Studio from Direct Out (as the DI track), add Git Mod from the Monitor Out and add Deley/Reverb Wet from the Main Outs ... or any other configuration. Adding S/PDIF to your workflow allows you to get the most out of your Profiler (up to 6 channels total to capture everything you might need).


    And even if you think you don't need anything else than Master Stereo and Git Studio (DI), you still save some of your few inputs on the interface for other purposes (Microphone? Keyboard? Any other outboard gear?). :)

    You guys are right, it's not quite as simple as I thought.


    For whatever reason, sometimes my S/PDIF connection is working flawlessly - other times there are constant drop-outs and stutters.
    When the problems start it doesn't seem to help to increase the ASIO buffer size, and I don't remember having problems when using the analog inputs for a while.


    Just had a re-amping session over S/PDIF that worked perfectly. Strange... ;)