Kemper Amps Forum

It seems that a thriller is going on the KPA forum.

Quoted from "miles"

I detect no change in aliasing with 1.0.9.7426.

I agree..I loaded 1.04 just to compare and see what mikeb meant..Note that I never used it before as I started with 1.06...I hear much less aliasing with this one

Wanna hear it ..just load those Cobra Randall MTS profiles ..and BTW that is thru Headphones

Aliasing sweep-test wise, this new V1.0.9.7426B rev sounds nearly identical to the v1.0.9.7415B version (meaning: noticeable aliasing when running amp & stomp together) except that the stomp section alone now has a little bit of digital artifacty clicking going on. In other words, the stomp in solo mode (which is not bad) has a bit of random grit noise now. You can hear the new rev in Test 7 below, and the digital clickiness difference in Test 8.

In fact, the digital artifacting is getting more of my attention now. In the previous (some of the earlier) revs I noted a bit of unexplained 'grit' in the amp model, which is still there - and one of the components of this grit sounds like the Stomp Grit Difference that you can hear soloed in Test # 8. Could the KPA be taking too long processing some of its samples, causing them to skip? Funny how you don't hear this grit on the combined Stomp+Amp tests.

If you go and revisit the demo at KPA Aliasing Test Suite, you'll see eight files:

1 ) KPAaliasing Test - Original test using original v108 firmware and patch
2 ) WQ 104 Patch A - using v104 firmware and patch A (probably using my original demo WQ patch)
3 ) WQ 108 Patch A - using v108 firmware and patch A (again, probably using my original demo patch - this result behaves like Example #1)
4 ) WQ 104 Patch B - using v104 firmware and patch B (probably using the factory restored WQ patch)
5 ) WQ 108 Patch B - using v108 firmware and patch B (again, probably using the factory restored patch)
6 ) WQ 109 Rev 7415 Factory Restore
7 ) WQ 109 Rev 7426B (newer v109) <- NEW
8 ) WQ 109 Rev 7466B - Rev 7415 Stomp Residue (digital difference between new v109 and old v109 for just the stomp) <- NEW

-djh

So the 8th clip is the digital difference between 7426 and 7415? The "crackle" you hear is the difference?
What exactly does this mean? Could you elaborate on this?
If there was to be no difference - would we be listening to a silent sound in the 8th clip?

(Wow, 5 questions in a row!! Sorry for that )

Schneidas,

a) Right, exactly. The 8th clip is what you get when you subtract the stomp performance of Test 7 from Test 6. The "crackle" is the difference.

b) I edited my post above to make a flailing guess. Maybe something's changed that's caused some samples to take too long to process, and it's causing some sample ticks to be missed over S/PDIF. Who knows? I'm guessing wildly here.

c) Correct! If there was no difference, it would be dead silence. For the record, the FX bypass (test subpart #1) sums to null, the stomp solo (subpart #2) sums to crackle, the amp solo (subpart #3) is too different to sum, and the combined test (subpart #3) is also too different to sum. (Although, parts 3 & 4 do -sound- very similar)

-djh

Very interesting! Thanks for clarifying that.
Looks like there's still work needed to be done then...

Quoted from "dhodgson"

Schneidas,

a) Right, exactly. The 8th clip is what you get when you subtract the stomp performance of Test 7 from Test 6. The "crackle" is the difference.

c) Correct! If there was no difference, it would be dead silence. For the record, the FX bypass (test subpart #1) sums to null, the stomp solo (subpart #2) sums to crackle, the amp solo (subpart #3) is too different to sum, and the combined test (subpart #3) is also too different to sum. (Although, parts 3 & 4 do -sound- very similar)

-djh

Ok, now that I thought about it, I got another question.
So you digitally substracted the audio of FW 7426 from FW 7415.

If FW 7426 has less noise (so a positive outcome of the substraction): the resulting sound we hear in clip 8 will be this "crackle".

If FW 7415 has more noise (so a negative outcome of the substraction): the resulting sound we hear in clip 8 will still be a "crackle", right?

So, how do we know if the outcome is *positive* or *negative* - meaning 7415 is *more* or *less* aliasing from the 8th clip?

Schneidas,

As far as the solo stomp aliasing is concerned, the two are virtually identical. It's the crackling that's new - you could subtract the 2nd from the 1st, or the 1st from the second and hear the same noise ('tho the polarity of the crackle would be flipped.)

For clarity's sake, the amps in both versions crackle a bit - but the solo stomp only crackles in the recent rev.

-djh

Quoted from "dhodgson"

'tho the polarity of the crackle would be flipped.)

Ah, this!
Ok. I got it now! Thanks