Kemper + Logic + Gain = Uneven latency

  • Hi all! So I've been reamping a lot of DIs lately and I have come upon a weird problem, which is that anytime I use a rig with a lot of gain (unclear how much gain since my rigs are mainly totally clean or a fair amount of gain) the latency when reamping is not consistent. At least that is what the I/O plugin in Logic tells me, and to some extent my ears as well.


    Basically, when I reamp, I run the DI via S/PDIF between the Kemper and the Crimson. When I'm happy with the sound I'm getting, I put the I/O plugin on the DI track, run it through the Kemper (by pinging it a few times) and then make note of the latency. I then compensate manually for the latency by using the 'Recording Delay' in the Audio settings, before I track that particular part. I don't track through the I/O plugin or anything (and I make sure it's off when recording), rather I have the DI track's output going to the Kemper, and then I have a separate track with the input from the Kemper that I record to. For the most part this works fine and I get a steady latency when pinging the Kemper (usually around 380 samples or such). However, sometimes (and it seems to be related to hi gain rigs, though that's definitely only a correlation at this point) when I go to ping the Kemper I get wildly different results. The result may jump between 100 to 500 samples (and everything in between) every time I ping the Kemper. My main concern here is that this latency is uneven throughout the recorded track, making it nearly impossible to align perfectly. Now to be fair these are minor latencies but they're still on the audible side of things (around 8-10ms if my math is not completely off). Also, changing my i/O buffer doesn't really affect anything, and neither does the 'Constant Latency' button on the Kemper. Surem changing the buffer makes the overall latency smaller but the variations still remain.


    So the question is...why? Why isn't the latency consistent? Is it related to each rig? I tend to use the same amps for hi gain and clean sounds, so I guess it could be a problem with specific rigs. Is it my interface? Logic itself? Is it even a problem? Any thoughts?


    Cheers,
    Chris


    My Gear:

    - Audio 24-bit, 48kHz

    - Logic Pro 10.4.2

    - Macbook Pro (MacOS 10.12.6)

    - SPL Crimson

    - Kemper rack unit, latest stable firmware

  • That does sound strange, since you have constant latency engaged. It's a rather large discrepancy.


    When I've reamped previously, I've drawn in a single sample "pulse" in the audio file editor in logic on the source DI track - that gives a very clear transient you can use to align the reamped track to. I then manually move the recorded region to obtain the correct time of the recording. This, to me, seems simpler than the approach with pinging.


    I'd contact support, since it seems like there is something else going on.


    Do you have any plugins (other than the I/O one) loaded in the project when you do this? This may have an effect.