How Long of a Response Does KPA Capture?

    I think Kemper is the only one who can answer, but I'm wondering how long of a response the KPA is capable of profiling. In other devices, one can figure this out by knowing how many taps are in the Impulse Response for the speaker system. For instance, a 1024 tap IR will be about 21ms at 48kHz. The KPA obviously has some time limit regardless of what method it uses.


    I ask because there is clearly a time limit of what can be captured in the response of the amp to the test stimulus. I experience nasty artifacts trying to profile an amp with some ambient room mics. The KPA was basically seeing "reverb" and considering it a "time based effect". :)


    If we knew what the time limit was, I think we could infer the maximum safe distance a mic should be placed away from the speaker?


    Of course, in a really reflective room (like the one I was playing with), the whole room response needs to be taken into account for the time limit.

    Doesn't matter what Kemper uses - I tried to preempt this response knowing it was the probably the first one I'd receive. :) I blew it. :) I tried to use the IR example as a guide for how one knows the time cap in other modelers that use IRs.


    This is signals and systems problem - it's a math thang - there is a time limit to the "response" the Kemper can capture.


    The response here being the "response of the reference amplifier" - I'll put in it quotes to separate it from the response in Impulse _Response_.

    Ok, got it. Tough question. Some user (Armin) was able to profile with FF mics, other are having error messages already with the mic at 6" from the grid. I believe it has more to do with phase and interferences, but is just a guess. The technology behind is not public, so is not clear if it is still a time function or not. I do not believe it will be more disclosed in the near future.....

    "Music is enough for a lifetime, but a lifetime is not enough for music" Serghei Rachmaninoff


    I have tried profiling with room mic's and the results are less than satisfactory to say the least, which is a shame as I really like mic'ing up a room to get the full roar and breath of a speaker cab, but can't be done as Kemper do not capture enough information.

    Quote from blewis

    Doesn't matter what Kemper uses - I tried to preempt this response knowing it was the probably the first one I'd receive. :) I blew it. :) I tried to use the IR example as a guide for how one knows the time cap in other modelers that use IRs.


    This is signals and systems problem - it's a math thang - there is a time limit to the "response" the Kemper can capture.


    The response here being the "response of the reference amplifier" - I'll put in it quotes to separate it from the response in Impulse _Response_.

    Ah signals and systems, a man after my own heart. What's your background, Blewis?


    Gazing into my crystal ball, I suspect that the test tone section responsible for determining the cabinet response begins about two seconds past the end of "UFO" swells at the beginning. You've got an impulse, followed by a very brief (1.5mS) step function followed by about 240mS of silence then fourteen swells of a low level surflike noise lasting for about 13.5 seconds. The higher gain the amp, the quieter this section so it could be a statistical MLS-type of chip function that's trying to squeak by for measurement purposes without being clipped by the amp. So, whatever's going on it looks pretty clever and a likely good method for keeping all or part of the "room tone" out of the analysis of the profiled speaker's response. That would put a cap on far-field miking, but if that's your thing I think your best bet would be to an take an impulse of your room and convolve with that later at mix time.


    All of this is just conjecture, of course. ;)


    -djh

    I profiled both close miked and mid field = microphone about 1 meter distance from the speaker.


    The later sounded more 'in the room' for me - I did not try to use larger distance - say 3 meters.


    I found that the KPA is very sensitive to the level - the mic will deliver less level when miking at one meter distance - and that leads to strange sound here too.


    My first try was to rise the 'return level' but that leads to all kinds of unwanted side effects in the past - and in some cases still today.
    I got my workaround by using an external mic-preamp and increase the level so that 'return level' can stay at 0 - that works fine - at least of one meter distance.

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    Quote from dhodgson

    Ah signals and systems, a man after my own heart. What's your background, Blewis?


    I trained as an Electrical Engineer. Now days I have a Master in Spreadsheet Science. :P


    My math skills aren't what they used to be - 1's and 0's will do that to a guy - but I've still got a handle on the concepts.