SPDIF Output Levels

    I'm reposting this from the problems forum in case it helps someone else.


    Using SPDIF out on the Kemper into my DAW sound card I got clipping with most profiles without changing anything, much much too loud. Here is what I found:


    Inserting a Gain control on the SPDIF input (in my soundcard control panel software)allowed me to remove all clipping with all profiles. I had to drop the Gain by -11db(depending on profile). After this the Kemper sounds perfect. Exactly like the XLR outs. I didn't even know you COULD have a gain control on a SPDIF.. I probably don't understand SPDIF. I figured that a device cant send a SPDIF signal passed +0db but in this case I must be wrong about what is happening.


    Also, it helps to max the Master Volume even if you use the SPDIF (and the Master has no effect) because you can see if the output levels are clipping via the Clipping light.


    PS thank you C.K., your advice about changing gain controls along with statements about dropping overall volume levels by 6db got me on the right track.

    Edited once, last by mikeb ().

    Sounds like it's time to take some measurements again.


    -10dBFS from my DAW -> KPA over S/PDIF with Master Volume at 10.0 (not that it matters) and Volume at 0.0dB with Stomps, Stack and Effects Off should yield -10dBFS when echoed back from the KPA over S/PDIF out.


    But it doesn't anymore (It used to, for S/PDIF.) It currently reads -4.1dBFS, and since I'd left my analog calibration intact from the older firmware the analog line outs seem to reflect this as well (i.e., the line outs are running hotter as well.)


    Why is this so hard to nail down? C'mon Chris, this is the easy stuff!


    -djh

    I also have to report that profiling a modeling stomp box yielded input being overloaded when profiling, no amount of fussing got the level from the direct output send low enough.


    Conclusion: direct output send out is too hot as well, I suppose if i had a mixing board I could compensate, but as is, the direct out does NOT send the same level as what goes into the INPUT.


    [edit] playing during profiling is what I mean, when I try the direct out in browser mode, the levels are the same.

    Edited once, last by mikeb ().

    I have found this too when profiling amps. A very hot sound is going out of the direct out and I don't like it. I deal with it by altering the input sensitivity settings and inserting 'the pot' pedal between the kemper and the amp. I really would like the sound from my amp via Kemper direct out to be the same as it is when I go direct into it with my guitar.

    Vintage amp obsessive


    Yes, it's easy.
    Please check the Clean Sense parameter in the input section. It has an impact on the pure input gain, while not changing the gain of distorted sounds.

    This is a bit confusing.
    Where do the profiles clip? In the KPA or on your DAW?
    The Master Volume has no effect on the level LED.

    Quote from ckemper

    This is a bit confusing.
    Where do the profiles clip? In the KPA or on your DAW?
    The Master Volume has no effect on the level LED.

    Ok I was incorrect about the Clipping Light, my bad.


    The clipping is in my DAW which is a EMU 1212M based computer setup. I am running the SPDIF out from the Kemper into the SPDIF in on my soundcard, set to slave. The clipping generally occurs with palm mutes, when the bass tones are the strongest. I have never experienced SPDIF clipping before. Not sure why the Kemper is so loud in this respect.

    Quote from ckemper

    Where is the clipping showing up exactly?
    In the DAW?
    Monitor speakers?

    For me The spdiff levels are way way too hot with rig volume on no 2 its ok but anything louder and it clips from the kemper thats on every profile without exception i have been able to compensate by lowering the spdif levels on my sound card but not everyone has this choice with their soundcard. Please Christoph put the spdiff volume level on the master volume again i cannot understand why you removed this crucial feature?

    Quote from ckemper

    Yes, it's easy.
    Please check the Clean Sense parameter in the input section. It has an impact on the pure input gain, while not changing the gain of distorted sounds.


    There we go - Clean Sense of 5.0 seems to do it, Stomps off, Stack Off, FX off, Master@10, [email protected], [email protected]. I'll be using that as my unity gain reamping calibration reference henceforth. Hoorah!


    [Edit: Just Discovered: This won’t yield a distortion-free signal when reamping through the Instrument Input, possibly because of a soft-clipper at the input of the KPA that you can’t completely turn off. You can reduce the Clean Sense to 0.0 to reduce the harmonics though, but if you do you’ll have to raise the Volume to max +12.0dB to make up for it.]


    -djh

    Edited once, last by dhodgson ().

    Quote from ChrisBeaver

    For me The spdiff levels are way way too hot with rig volume on no 2 its ok but anything louder and it clips from the kemper thats on every profile without exception i have been able to compensate by lowering the spdif levels on my sound card but not everyone has this choice with their soundcard. Please Christoph put the spdiff volume level on the master volume again i cannot understand why you removed this crucial feature?


    Got to ask you too:
    Where does the clipping occur?
    If you have something clipping by SPDIF, the is something wrong with the setup after the KPA.

    Chris,


    S/PDIF reamping with the Clean Sense at 5.0 is working as expected, thanks for the tip. My observation up above was regards to reamping via the Instrument input. Having performed a nice clean REAMP over S/PDIF as described, I then sent a sine tone from my DAW to the KPA's analog Instrument input and began adjusting my REAMP's output trim until, once again, I was reading -10dBFS at the KPA's S/PDIF out. At that point I'd tweak the line trims on my Saffire until the analog outs from the KPA were also reading -10dBFS there.


    Anyway, this is all stuff I'd done before in earlier firmware, very straightforward. But this time I put a spectrum analyzer on the KPA's return signals to see how clean KPA's virtual passthru was, and... not very. When reamping through the Instrument input. I was having to reduce the Clean Sense to 0 and reduce the test signal being sent by more in order to get the same kind of distortion-free reamp loop that I would when reamping via S/PDIF. With everything properly gainstaged, I would expect that analog reamping would be nearly as distortion-free as digital reamping; certainly, the Input and Output lights on the KPA were well in the green here.


    So that worries me a bit - if I've got a clean guitar track that I want to reamp and all processing is bypassed, I'm not expecting to see soft-saturation harmonics via one method and not the other. Kinda odd!


    [DANG. And today, I tried this again after a fresh reboot and the problem went away! Dang Dang Dang! I'm going withhold judgement on this until I can make it happen consistently]


    -djh

    Edited 2 times, last by dhodgson ().