Bass articulation / accuracy in high gain profiling

    Hi-


    First post, thanks for having me. Still getting acclimated to the Kemper, and have not yet nailed my main amp, a Cornford Hellcat. In particular, I'm having trouble getting accurate dynamics when then gain is on.


    Here's a quick A/B. Signal chain:


    Les Paul Classic -> Hellcat, red channel, max gain -> pine cab -> H30 -> SM57 -> JLM Audio preamp -> Kemper -> Lynx Aurora -> Macbook.


    Amp clip:
    https://soundcloud.com/graphics8/hellcat-amp


    Kemper clip:
    https://soundcloud.com/graphics8/hellcat-kemper


    What I'm hearing here in the Kemper track is over-compression, particularly in the bass. Whereas the amp track is stiff and chuggy, the Kemper track sags. This squishy sound is not unlike what happens when you reamp a track too hot into an amp. However both of these clips were live -- no reamping.


    In addition, the Kemper is picking up a ton of sub. The '57 does not put out much below 100hz, but the Kemper seems to think so. You should be able to hear this in good headphones or studio monitors. Additionally, here's the Match EQ curve in Logic:


    http://img542.imageshack.us/im…/hellcatkempermatcheq.png


    Aside from the huge bass roll-off, the rest of the curve is actually very close. Reasonably flat from 200hz to 1k. And dead flat from 1k to 10k. You can click this curve on and off in Logic and the mids and upper mids sound essentially identical.


    So... If this were a real amp, I'd assume I was simply going into the amp too hot. The Les Paul has a 500T in the bridge which is a very hot pickup, but I have the "Clean Sens" at 4 and I'm not getting any red lights.


    Dropping the gain (or "Dist Sens") doesn't help - that just reduces the overall saturation, not the bass strangulation that's happening here.


    Definition is already at 9.7 -- nowhere to go from there.


    Filtering out bass using "Studio Eq" before the stack just eviscerates the sound. And frankly should not be necessary if the profile is correct.


    As an additional test, I installed the "Hellcat Red Channel" profile from the rig exchange, increased the gain to 7.5 to match my profile, and swapped cabs with my profile. Here's what that sounds like:


    https://soundcloud.com/graphics8/hellcat-red-kemper


    Still pretty squishy.


    Thoughts? Is anyone else having this issue with high gain profiles?


    FYI:


    For the "refining" phase, I simply played the same riff a few times. From the manual, Wiki, and forum, there seems to be endless speculation and no real consensus on what the box actually needs to hear during refining. My own experimentation has produced widely varying results -- "definition" values and frequency curves all over the map. For the mean time, I've settled on using the test riff itself to introduce the fewest variables.


    Moving forward, more transparency on the refining phase would be welcome. If any guitar will suffice, as the manual states, then the Kemper should probably just play its own refining signals to eliminate the needless fumbling in the dark. By comparison, creating IRs of speaker cabs is a clear-cut, repeatable, and highly accurate process.


    Thanks!

    +1 to what tyler just said.
    I just profiled a Hellcat this last week with no problems at all, so its dooable with what you have.
    the return level can be a bit of a pain, but try to let it be at 0DB for the best part.
    this means with a 57, the input may seem to quiet, but the kemper does auto-adjust the volume at "store" time.

    Thanks for the speedy response guys. So you're saying the compression issue is not typical of high gain profiles and can be avoided?


    Re: Miking directly into the Kemper, will give it shot once SnowPocalypse II blows over. That being said, the JLMs are nice pres and part of the sound of my recording chain. Are we saying that optimal profiling really only happens when jacking a mic directly in the back?

    Quote from hm2

    Are we saying that optimal profiling really only happens when jacking a mic directly in the back?

    No, i always use a small mackie submixer before the KPA. If you´re using condensers which need phantom power this is the only ways to do it. However several other users who also used special mic preamps reported suboptimal profiling events. Perhaps it might be the internal compression which has an impact on the dynamic profiling.

    Quote from hm2

    Thanks for the speedy response guys. So you're saying the compression issue is not typical of high gain profiles and can be avoided?


    FYI
    some of the most discriminating producers and players (Andy Sneap, Ola Englund, Keith Merrow and many more) are getting great, accurate results from profiling hi gain sounds. ;)


    like already suggested, I'd recommend to plug the mic directly into the Profiler for now and to watch your levels.


    let me know how that works out for you.

    Big fan of Sneap's approach, and super chill nice-guy attitude. I've seen his Kemper video, but I can't really tell from the Testament clips he plays if he's getting the same sort of artifacting I'm getting. Given his ears, I would have to think he'd hear it if he was. It could be that this issue is specific to the Hellcat.


    Will try the preamp-less approach and report back.

    Quote from and44

    +1 to what tyler just said.
    I just profiled a Hellcat this last week with no problems at all, so its dooable with what you have.
    the return level can be a bit of a pain, but try to let it be at 0DB for the best part.
    this means with a 57, the input may seem to quiet, but the kemper does auto-adjust the volume at "store" time.


    What happened with the return level?

    Hi Christoph. I once had it stick at its highest setting -- I kept getting "amp too noisy" errors and then I noticed what was happening and reset it. Not sure what caused that, but it hasn't recurred.


    When I'm running through my JLM pres, the return level is down around -20. Is 0db return level preferable over a negative return level? Presumably there is a preamp in the Kemper to handle directly connected mics. What return level is minimum gain on the internal pre?

    I found that unless you're profiling the amp at a spectacularly loud volume then you really need a pre with any mic at all, including the 57/58, otherwise it's whisper quiet coming in and you just got a tonne of noise.


    The sound you get should be close to identical, however a major factor can be room noise, I'd say though that in this instance the major culprit is your refining. I'm not sure why people keep on pushing out the idea that you only need to refine with a few loud chords as in the videos (despite the fact that even in those videos you can clearly hear quite a large difference between profiled and original), because it's total bunk in my experience, you need to sit down and refine for quite a while like 5-10 minutes or longer, and then you need to re-amp and record the results in order to actually compare the profile vs the original (because the Kemper doesn't yet have a looper and the ability to do this for you, which was an idea I suggested a while back), it's a bit of a convoluted process but that way you will be able to refine to the point of having a far more accurate profile. Doing that, and being willing to throw out a profile if it's just not going in the direction you want will get you the result you want, it took me quite a while before I started getting profiles that were close to the source material here.


    The other thing before I forget, is leave every single one of the dials at their default (typically <0.0>), don't add any bass or treble before you start, try to profile with the gain at 0 too, however set the gain dial where you think it should be as the KPA seems to need a little help. Bear in mind that the profile will take it's other settings from the current profile you're using when you start the process, so if that has some crazy amp block settings or stomps or effects enabled, then expect to see them on your brand new profile too. So that means it's best to start out with a profile that's as neutral as possible without any effects (especially as it'll apply the same effects and additional tona stack to your original amp when you're A/Bing, which makes profiling quite a bit harder if they've been adjusted from parity).


    Anyhow, I'm sure you'll be bale to get that tone, but good luck with it.

    After reading this I'll never make any Profiles.
    Is it really this complicated?

    Quote from Guitartone


    After reading this I'll never make any Profiles.
    Is it really this complicated?

    Well, i don´t claim to have a super good hearing sense anymore after all that teenage years of unprotected ear destruction but i was very lucky that my stuff worked right from the start. A lot of those cab profiles were done 15 minutes after unpacking the KPA. There may be some stuff that profiles not that easily, but 95 % of what i feeded the KPA came out very nice.

    Quote from Guitartone

    After reading this I'll never make any Profiles.
    Is it really this complicated?


    It's not really complicated at all, but it is time consuming if you want to get the best possible result. If Kemper were able to introduce a looper tool (though I've no idea if there's enough RAM for this, or if not whether the USB connection would be fast enough to allow the use of the USB stick), then it would be hugely streamlined as a process as you could get the Kemper to loop record the amp and the clean signal and then play it back during the A/B comparing process, A being the recorded amp loop, B being the dry loop but played back through the KPA so then you'd be able to adjust settings on the fly without playing guitar at the same time and hear the two in isolation without the amp blaring out and without having to manually re-amp and record both in order to compare the results.

    Wow, thanks for all the details Per.


    I've put in a little more time on this, and more or less just by repeating the process, I've got a handful of profiles that are much closer. Here's the new A/B:


    Hellcat Amp2
    https://soundcloud.com/graphics8/hellcat-amp2


    Hellcat Kemper2
    https://soundcloud.com/graphics8/hellcat-kemper2


    The squish is still there on the chugs, but less evident. This was basically luck of the draw. As a test of all the suggestions above, I ran a bunch of profiles with and without preamps, and with various lengths of refining times. There were close matches among all of these combinations. This one happened to be straight in, bypassing the preamps, with a short refining time -- one or two minutes, again playing just the test riff.


    With no further processing in Logic, here's what the match curve looks like:


    http://img90.imageshack.us/img…hellcatkempermatcheq2.png


    Still a big rolloff necessary in the bass, but quite flat above that. With a simple high-pass in Logic at 100hz, 18db slope, this is what the match curve looks like:


    http://img24.imageshack.us/img…llcatkempermatcheq2hi.png


    Flat. In the Kemper clip above you're hearing the hi-pass.


    So. What's the takeaway here? I've probably profiled this amp about twenty or thirty times now at the same settings. To those who may be daunted by the widely varying reports of the profiling process, here are my seat of the pants conclusions:


    1. I don't see a huge correlation between preamps / no preamps as far as accuracy is concerned. All you guys with your Neve 1073s, more power to you.


    2. There doesn't seem to be much correlation between refining time and accuracy. I did one for 7 minutes that was over-compressed squashed, yet this one above was only a minute or two. My best guess is that once the box hears what it is looking for in the refining process, further playing is simply moving those values around. This is good news, since the manual has almost no instructions for correcting things you hear during refining anyway. You may as well just profile the amp a handful of times, with some basic refining each time that reflects the types of riffs you plan to play. Because there's some analog voodoo in the process, you'll get different results each time. Pick the one that's closest.


    3. When it comes to frequency response, the Kemper's match eq is really accurate from 200hz all the way to 10k. Preamps or not, long refining or short, that part of the match curve is usually pretty spot on. Kudos.


    4. Bass accuracy and compression seems to be its achilles heel. I ran a handful of crunch profiles, and bass content below 200hz was almost always overblown. My guess is that this is simply more evident in high gain profiles, where excess bass results in excess compression -- much the way feeding too much kick drum into your mix bus compressor will take down your whole mix. I suspect certain amps are tougher for the Kemper to profile in this respect. The Hellcat may very well be one of those, since in reality it exhibits very controlled bass response at high gain with no squish at all.


    To be fair to the Kemper, overblown bass is an issue in real high-gain amps as well. Amps like the 5150 bleed off bass in between gain stages to keep this under control. You can't simulate this by turning down the overall gain, or lowering the bass eq on the amp. The Kemper's "definition" control may work this way, as it seems to reduce the squish somewhat. I can't really tell. But the most accurate profiles I did were the ones that came out of the oven with lower definition values *and* less audible squish to begin with. This is where the profiling process gets black box. In the clip above, definition was set at 7.5 after the profiling process and that's where I left it. Again, luck of the draw and simply a result of running multiple profiles.


    Moving forward, I'd love to see the profiling algorithm improve when it comes to crisp bass response at high gain. Or at least some more exposed parameters for adjusting preamp compression, or thinning bass response inside the preamp, to alleviate the sag.


    Nevertheless, quite a disruptive little piece of technology. Again, kudos.


    Thanks!

    Great post, now share the Profiles. :D

    Nice thread hm2.. Appreciate the soundcloud link comparisons.. My experience has been simmilar to yours in the fact that some of my better profiles have seemed to be the result of dumb luck - I take the non scientific approach of trying a lot of things then pick the best profile of the bunch at he end.
    Is your preferred profile on the rig exchange? Would be cool to throw it out there and see if any of the more experienced users on here can chug up the bass response post profile..

    hm2,


    while you certainly seem to have issues to get the profile you want from your current setup, attributing this to shortcomings of the profiling process seems like a knee-jerk reaction.


    Consider this:
    - thousands of spot-on profiles have been made already from all kinds of amps (including many higain ones)
    - Andy profiled a Hellcat just last week and he said he had no problems with it


    Contact me via pm for support.


    thank you
    Don

    Hi all -- thanks again for all the input. Good news, I've got bit of a hack that works pretty well for nixing the compression issue: MXR 10-band eq pedal during refining. Here's the skinny:


    Amp:
    https://soundcloud.com/graphics8/hellcat-amp3


    Kemper:
    https://soundcloud.com/graphics8/hellcat-kemper3


    The dynamics are now very similar, and personally I'm hard-pressed to tell the difference. This was done with the MXR between the guitar and the Kemper during refining. All three bottom bands -- 31hz, 62hz, and 125hz -- full cut, -12db. The 250hz band only a quarter cut, about three db. Bingo.


    Note that with the eq, you're not looking to alter the frequency response of the resulting profile. You're really just looking to influence the dynamics/distortion modeling in the refining phase. For whatever reason, filtering out the bass during refining does not create a big hole in your tone -- the resulting profile still has plenty of sub. It simply causes the refining algo to remove sub from the distortion path, and that creates more headroom, less compression, and life is good.


    Fyi this was done with my preamps inline, at a return level of -22, and a short refining phase of about a minute. It's also highly repeatable -- I ran this multiple times in a row on the same settings and got pretty similar results each time. The "definition" parameter wandered a little, between 6 and 9, but the frequency response was identical, and the results always sounded the same. I'm pretty much convinced at this point that the manual can be taken at face value on the refining process, in that nothing particularly special needs to be played here, and that super long playing times are not really necessary.


    Don -- thanks for your attention here and no intent on my part to sound overly negative. I have to laugh that I can post a thread with "problems" with a space-age device from Germany that exactly recreates the sound of my expensive boutique amp from England so I can play it in my living room at whisper volumes at 3am. Next I'll be complaining about the price of gas in my Lamborghini. As Louis CK once said, everything's amazing and nobody's happy!


    I'll upload the final profile to the rig exchange for those who'd like to try it out.


    Thanks!

    Now I'm really looking forward to this Profile. :)


    Now that you're happy with it and have it saved, out of interests sake, have you tried your Profile with a different cab, perhaps a Tills cab?