SPDIF seems to work but is it really?

  • Hi,


    I have an Apogee Symphony I/O that I run in USB mode. Unfortunately, using USB, the Symphony can not lock to external digital sources. You need Thunderbridge for that.


    That being said, I still hooked up the SPDIF between the Kemper and the Symphony, and I was able to record and reamp using the SPDIF connections.


    I was surprised this worked as I understand the Kemper can't lock to an external digital signal, and thus both clocks would be running independently. I called Apogee, and I was told, they are probably running so close that you aren't noticing, but you are still probably getting subtle aliasing and drift. I'm wondering if it is this, or did the Kemper OS get updated to be able to lock to an external source?


    thanks,
    joey

  • I found this on SOS


    Quote


    "However, if the receiving device is configured to use an entirely different clock source as its reference (perhaps its internal clock, or the clock from a different source) then the two devices will effectively be working independently of one another and will drift in and out of sync with each other. If you are lucky, most of the time the two clocks will be close enough that when the receiver goes looking for a sample from the source, it will find one. However, sooner or later the receiving device will look for a sample and not find one, and that's when you'll hear the click! The rate at which the clicks occur is an indication of the rate at which the two clocks are drifting relative to one another. I came across one professional installation with asynchronous clocks where the clicks only happened once every several days!"


    So I guess, my follow up question would be... if they are running independently but so close, and I'm not getting any clicks, does that mean I'm all good? I could live with a click every once in a while, and just reamp again.


    Or is it a more subtle degradation, and I'd be better off just reamping analog.

  • Clips, crackle, hiss. All kinds of artefacts. It might not be immediately evident, but you will catch it later perhaps, a little ghost fizz or scratch. Ideally, you should be slaving the UAD to the Kemper for best results. Alternatively, use the 1/4" outputs.



    EXACTLY :thumbsup:


    And a huge factor for why we need to SLAVE the KPA in lieu of being the MASTER!! I'm surprised that this item isn't rated higher on the wish list board... but hey.. not everybody uses it for digital recording.... I guess..

  • Yes, it's the fear subtle distortions that have convinced me this is a bad idea.


    I can forgive Kemper for not implementing slaving, but I have a harder time forgiving Apogee for not implementing slaving in USB mode on the Symphony I/O.


    It means I will be turning off my $3000 Apogee interface, and buying a $200 Roland or Native Instruments interface that can slave.

  • It means I will be turning off my $3000 Apogee interface, and buying a $200 Roland or Native Instruments interface that can slave.


    Dude, that's sick!!! I've been considering the Symphony for the past few months to replace my Yamaha 01V96i but now... no way!! Yeah, the sync issues been documented for quite some time now by Apogee; seems it'd be fixed by now..


    Hey, the Focusrite Scarlett 18i8 worked flawlessly for my on a remote session in LA a month or so ago.. no issues with the S/PDIF and the analog I/O sounded great... cheap too when you buy used.


  • Dude, that's sick!!! I've been considering the Symphony for the past few months to replace my Yamaha 01V96i but now... no way!! Yeah, the sync issues been documented for quite some time now by Apogee; seems it'd be fixed by now..


    For full disclosure, there are 3 ways to connect the Symphony I/O to your computer. USB, Thunderbridge, and PCIe card. Slaving works with Thunderbridge and the PCIe card, just not USB. But Thunderbridge is an extra $500, and PCIe is another $900. I don't have a Thunderbolt port on my computer, so that means I would have to buy the PCIe card, but I don't want to spend $900 on PCI technology that Apple has said they will never put in another computer. I will get the Thunderbridge once I get a new computer, but that is probably a year or 2 out.


    ...and thanks for the Scarlett recommendation, I will check it out.

  • Cheapest solution? Record and reamp with analog 1/4" inputs. Its not a big deal, just made out like there'll be better tones from SPDIF. I actually like the sound of the Kemper through 1/4" vis-a-vis SPDIF.


    I mean, you've heard the story of Eddie Van Halen's 200-feet cable runs, right? All of it contributes to your tone, no right or wrong way to do many things.

  • Sorry for asking a newb question but if it's being transferred digitally through S/PDIF, what's with the clock sync? Shouldn't bit for bit be transferred regardless? I'm completely lost here so bear with me please :). I basically unpacked the thing, hooked it up and played happily through the normal outputs but am about to start recording some stuff so while on the subject of S/PDIF...


    I've got a DAW with 4 channels so here is my idea:
    Record the dry amp plus the raw guitar signal through (S/PDIF) on channel 1+2. In the same time have the normal outputs for the Kemper to feed my FX and possibly record that on channel 3+4 on my DAW. Later I'd be either using plugins for FX on the dry amp signal (from CH1) or stay with the recording on 3+4 for a wet/dry/wet thing
    Am I onto something here or am I far off?


    My understanding is (was) S/PDIF is be the most optimal way of transferring what actually comes out of the Kemper (no unnecessary AD/DA going on), right?


    Now another question, is there a latency in the S/PDIF connection? To stay with my present DAW I will need a coax to toslink adapter, anyone has any experience with that? Will that add latency? I'm thinking electric - optical - electric..
    Am I better off getting another (cheap) DAW that does support coax S/PDIF and just aggregate the DAW's on my Mac Mini?


    Again, I'm all new to the Kemper as well as advance home recording/reamping so please excuse my ignorance.


    Cheers!

  • Cheapest solution? Record and reamp with analog 1/4" inputs. Its not a big deal, just made out like there'll be better tones from SPDIF. I actually like the sound of the Kemper through 1/4" vis-a-vis SPDIF.


    Yeah, that was my final decision rather than spend more money and deal with switching back and forth between interfaces. Plus, I want to reamp through my pedalboard anyway... ;-)

  • Sorry for asking a newb question but if it's being transferred digitally through S/PDIF, what's with the clock sync? Shouldn't bit for bit be transferred regardless?


    My understanding is (was) S/PDIF is be the most optimal way of transferring what actually comes out of the Kemper (no unnecessary AD/DA going on), right?


    Now another question, is there a latency in the S/PDIF connection? To stay with my present DAW I will need a coax to toslink adapter, anyone has any experience with that? Will that add latency? I'm thinking electric - optical - electric..
    Am I better off getting another (cheap) DAW that does support coax S/PDIF and just aggregate the DAW's on my Mac Mini?


    When two digital devices are transferring bits between them, one must be the clock master, and the other must lock to that master clock. If both are acting on their own clock, the transfer of bits won't be synchronized and errors will occur. The short story is the Kemper must be Master, and your spdif interface must be set to slave to incoming spdif. This is because the Kemper can only be master, because slaving hasn't been implemented by Kemper. I'm not sure if it is possible or not for them to implement that in the future???


    Yes, it is most optimal with respect to being less AD/DA going on.


    I'm new, so take this with a grain of salt. For recording, the way I planned to record if I could do spdif, was to monitor using the audio outputs on the kemper into my analog mixer, and just record the spdif, not listening to it as I play. So the only latency would be that of the Kemper which I guess is 3-4ms, and a little more if you choose fixed latency. For reamping using spdif, I am guessing there would be next to no latency as there are no AD/DA stages?

  • Less AD/DA. More AD/DA. Who cares? My thinking is that with better synchronisation between devices and less "jitter' in the time code, modern technology pretty much obviates the possibility of data getting lost. Is there a difference in the sound? Yes, but I'd leave that to preference. Going analog could give you a better tone than going via SPDIF, there are so many things that could result the tone: the profile, the capables, the converters. Is the sound good? If so, why nitpick about what isn't happening. I've recorded and reamped via SPDIF and via 1/4" I really don't think there's much of a difference.


    For people looking for a soundcard, the best you can do is get something with both options. Do your research, so you don't wind up in an unfortunate situation like the OP, where he has the connection, but can't slave his interface.

  • As a professional video editor for 30 years, keeping my video content in the digital realm was always important so as not to lose resolution when doing visual effects or creating copies of finished spot. I tend to approach audio as an amateur in the same manner, though I can see it may be over kill. Luckily the Focusrite Scarlet 6i6 this forum suggested I get gives me the option to go analog or digital in my home studio. I like having a choice.

  • I confess I can't tell the difference between using SPDIF and Balanced 1/4" and XLR with the Kemper recorded.


    I suspect, like with a high end microphone that has a low noise floor, you hear the difference when you start stacking tracks. Then the lack of resolution is additive.


    Is it additive geometrically or asymptotically (logarithm)?

  • So for purely workflow reasons, not sound quality, I changed my decision, I do want the spdif option.


    I called Apogee and they went out of their way to find one of their dealers that had a used PCI 64 card for a great!! price, so I'm all set.


    So thank you Apogee!!