You are not logged in.
Dear visitor, you are currently not logged in. Login or Register as a new user .
Friday, May 25th 2012, 3:10pm
RE: OK, a practical and simple example
Anyway, here's a pretty pure demo of the effect using the "Wet Queen" patch that began this thread. It contains Four tests of a sine tone fundamental simulating a bend and release from the 22nd fret to 26th fret on guitar (i.e., 1174Hz to 1479Hz, D to F#) using "Wet Queen" digitally reamped via S/PDIF @ -12dBFS.
Pass 1: All Effects Off
Pass 2: Only Stomp "B" enabled (Metal DS Drive cranked to 10 to exaggerate the effect)
Pass 3: Only Stack section enabled
Pass 4: Stomp "B" + Stack section
KPA Aliasing Test Demo
Excellent work, I can hear it very well now!
With a real guitar to notice it I have to do a very slow bending in that very high position of the neck.... and I can't hear it without the Metal DS Drive.
BTW, I tried with some software simulation (Mainstage) and with very high gain I have the same aliasing with that slow bend and release... are you telling me that the Fractal and the Line6 doesn't do it at all?
Just for curiosity because I will never go back from my KPA to those things...
Friday, May 25th 2012, 5:39pm
RE: OK, a practical and simple example
That is a well done demo, and is revealing in the context of a sine wave test, but it seems like in my demo of actual guitar notes KPA Aliasing Test (by Miles), that the aliasing noise has a little more thickness to it, and is slightly more up front and noticeable than Pass 3 of your sine sweep test. Though the aliasing noise in the amp profiles is generally somewhat subtle, it's important to accurately represent it in a guitar playing context. It's always good to have another perspective, so thanks for that.
Anyway, here's a pretty pure demo of the effect using the "Wet Queen" patch that began this thread. It contains Four tests of a sine tone fundamental simulating a bend and release from the 22nd fret to 26th fret on guitar (i.e., 1174Hz to 1479Hz, D to F#) using "Wet Queen" digitally reamped via S/PDIF @ -12dBFS.
Pass 1: All Effects Off
Pass 2: Only Stomp "B" enabled (Metal DS Drive cranked to 10 to exaggerate the effect)
Pass 3: Only Stack section enabled
Pass 4: Stomp "B" + Stack section
KPA Aliasing Test Demo
The noticeable thing here is that the distortion pedal is a much bigger contributor to the aliasing distortion than the amp model itself is. I've cranked up its gain to exaggerate the effect, but cranking up the Amplifier's gain is not as obvious as the pedal model. And combined, well - it's pretty clear. You can also hear a few clicks as I'm turning the Stomps & Effects sections on and off - they're not completely noiseless (but perhaps they should be; a 5mS crossfade would solve the problem.)
-djh
Yes, artifact-free in 2012 isn't too much to ask--if Line 6 can do it, so should Kemper. Much love to Kemper for creating the closest thing to an end-all-be-all guitar amp sim.
Friday, May 25th 2012, 6:12pm
Wow, nicely done. The aliasing effect in there would be this fluctuating sound you can hear in the background? I can hear that on the 3rd clip quite low but really fast and on the 4 clips much louder and fluctuating slower.
Right, this is the audio version of the "wagon wheel effect" that you see on film whereby the spoked wheels of a stagecoach appear to spin faster up to a point, then spin backwards and start to slow down. If the stagecoach keeps accelerating, its wheels will eventually appear to stop and start speeding up again in the forward direction. The effect is due to the spokes rotating faster than the frame rate (i.e., "sampling rate") of the camera can capture. You can see a simulation of this here.
So in the 2nd clip (stomp only) the effect is very straightforward to hear. The 3rd clip (amp only) has the same effect going on, albeit quieter and at a faster rate. There's also a lot of graininess going on at the beginning during its rise (but not the fall, curiously - this happens from 0:24-0:27) that I can't account for. Could this be the "wind howling noise" that Miles said Kemper was planning to fix in a future release?
Anyway, this test is the simplest case - a real guitar string may sound worse than this, because real strings are not pure tones - they have numerous harmonics each of which generates its own set of aliasing pitches. The reason that aliasing distortion sounds ugly and ring-modulatorish is because alias frequencies are usually harmonically unrelated to the source material.
Now, I don't have an Axe-FX or a POD HD, but I've yet to run across a piece of digitally distorting gear that didn't exhibit this behavior. If you don't hear it, it means you're probably not using the right set of probe tones to bring the behavior out.
-djh
Friday, May 25th 2012, 6:54pm
Although I have some sweet amps here at the studio, I've kept various PODs around since the beginning, and closely examined their aliasing, but when that HD came out, I was shocked at how devoid of aliasing it was. Perhaps I wasn't using the "right set of probe tones", but my guitars are very transparent through the POD HD. Sure, they improved the models a little bit, and it still has those unmistakeable POD tones
Now, I don't have an Axe-FX or a POD HD, but I've yet to run across a piece of digitally distorting gear that didn't exhibit this behavior. If you don't hear it, it means you're probably not using the right set of probe tones to bring the behavior out.
, but I'll be damned if they didn't nail a near-total aliasing-free sound. I rarely tracked my PODs and Amp Farm, but I absolutely plan on making records with the KPA, and is why I'm so enthusiastic to see it brought up to its ultimate advanced state.I don't have an Axe-FX either, nor have I played through one, but I would love to test it for aliasing--I have read that it doesn't have a problem in this area.
For a long time I was starting to think that digital distortion and aliasing were synonymous... until I heard the POD HD.
This post has been edited 1 times, last edit by "miles" (May 25th 2012, 7:00pm)
Friday, May 25th 2012, 7:00pm
It sounds like that to me.Wow, nicely done. The aliasing effect in there would be this fluctuating sound you can hear in the background? I can hear that on the 3rd clip quite low but really fast and on the 4 clips much louder and fluctuating slower.
Could this be the "wind howling noise" that Miles said Kemper was planning to fix in a future release?
Do you think that the more pronounced aliasing effect in the pedal block could be due to the pedals block running at a different internal sampling rate than the amp block? I think the amp block tube saturation simulation runs at 700 khz but maybe the pedal block do it at 44.1 khz. Maybe what I am saying does not make sense at all but that could explain as well why the fluctuation on the amp block is much faster and less noticeable compared to the one produced by the pedal block.
Similar threads
-
Feature requests »-
SPDIF Higher bitrate.
(Feb 7th 2012, 12:00pm)
-
- Problems and trouble shooting help »
-
Bend with 2 notes ore more, a.h, NUMERICAL NOISE !!!
(Apr 13th 2012, 8:29pm)
-
- Problems and trouble shooting help »
-
Digital artifacts when switching between presets while holding chords
(Feb 17th 2012, 11:02pm)