Critical! - Elastic Audio Rhythmic algorithm bug

[GeneOuse]

After a long time using EA and having random clicks/pops/artifacts with my drum tracks I decided to dig into it and figure out what's wrong - only to discover a critical bug with rhythmic algorithm at current EA state.

That's PT HD 7.4cs4.

It goes like this - enable EA on a loop/multitrack drum tracks to rhythmic algorithm with real-time processing. Quantize as needed and change the tempo by +/- 10 or 15 BPM to really emphasize what the bug does. Now go and delete all analysis markers and listen to what plays and compare it to the actual waveform. You will hear the ORIGINAL, unprocessed audio with some inversed artifacts at the end of audio but the waveform will look unchanged. In warp view all markers will look right, quantized and everything.
Now, to see the actual waveform changes that truly represent the current audio you need to switch to rendered processing. This doesn't happen with other algorithms and I know that rhythmic is designed to preserve phasing between multitrack drums so it's quite different.

Obviously, something is VERY WRONG right now as it turns out that deleting any analysis marker (while in rhythmic algorithm) will change audio in UNPREDICTABLE way. I should be correct to assume that if an analysis marker is not "activated" in warp view it should not make any changes to audio and should not interfere with manually created warp markers. Even if analysis info is deleted after warp markers have been activated and manipulated there shouldn't be any audible changes to audio.

Digidesign, please, let us know if it was meant to work this way or if it is indeed a bug.
As for me it is a very serious and disturbing issue as I constantly run into inexplicable artifacts. I can't be 100% sure that adjusting Elastic Properties window settings on separate tracks and then quantizing/manipulating grouped tracks won't give me some nasty artifacts at the end.

P.S. - haven't tried the same on a Mac yet but will try sometime.

[PaulV]

Yes, what you describe is the correct behavior, and not a bug - having correct analysis markers at every transient in the audio is essential for correct processing of the audio by the Rhythmic, Polyphonic, and X-Form algorithms. Changing them affects the output of those plugins, since they work to preserve transient attacks in the signal, and are guided by the analysis markers to do so. Each algorithm processes the audio in a different way, so each responds to missing transients in a different way. Having the correct analysis markers is important enough to the elastic processing that we provide the analysis view in order to give the user a chance to correct them.

The waveform drawn for stretched audio when using realtime processing is just a rough approximation for visual purposes (in fact, it's always the Vari-Speed waveform that's drawn) - use render mode if you'd like to see the waveform of the audio that's coming out of the Elastic Audio plugin (or bounce it to another track, as with other types of plugins).

Just curious, why are you deleting all the analysis markers? You shouldn't need to edit the analysis unless you notice that the default analysis mis-identified some of the transients.

Is the distinction between analysis markers and warp markers confusing perhaps?

[GeneOuse]

Thanks for clarifying on this issue. Just so there's no confusion I do understand the differrence between warp and analysis markers.
My concern is this - manually created warp markers do not work at all in rhythmic algorythm. You must have an analisys marker which you activate in warp view to use it. In all other algorythms manual warp marker will let you make changes to audio whereas in rhythmic a manual marker is just a line in the warp view that does absolutely nothing.

You can see how that can make it confusing to use EA on drums.

This also explains how a missing analisys marker can create artifacts in audio where you'd excpect a manual warp marker to fix things as it does in other EA modes.

[GeneOuse]

One more thing - I don't usually delete analysis info but in this case I did so to figure out artifacts issues I was having.

[PaulV]

Yes, what you're describing is mostly correct. To phrase it a different way, with the Rhythmic algorithm, warp markers have no direct effect on the decay timing of individual drum hits, only the timing of the attacks, and then only if the attacks are properly identified with analysis markers. So unlike the other algorithms, if you warp areas between analysis markers (which is usually the "tails" of the drums if the analysis is accurate), the output won't change. The Rhythmic algorithm takes a fair amount of liberty with the decay beyond the transient, and you can control that via the Decay parameter of the Rhythmic plugin window.

But it's not quite true say that warp markers do nothing with Rhythmic - what they do is determine the timing of the nearby transients (like drum hits) that have analysis. And in that regard, it's well-suited for drums since it guarantees the audio at every marked transient will line up exactly where you see it on the screen.

[NickH]

Hi Paul,

Just out of curiosity, do you guys know about the loud clicks you get between a warped region of audio and the fade applied to it afterwards? It’s very noticeable on the Rhythmic algorithm on tom tracks, of you cut them out & use a fade to damp down the resonance.

This happens whether you have the auto fade in/out in the prefs set or not.

I can supply audio and screenshot evidence if that helps…

Cheers

N

[NickH]

Looks Like this is a known issue on OSX..

http://www.digidesign.com/index.cfm?...1&itemid=28334

Can you confirm that you know about it on XP also?

N

[Guim]

I've discovered that behaviour a while ago in a sound design class. I did create an event marker in analysis mode to help me to stretch that region and found that it change the way how EA in rhythmic mode works. Thanks again to let us know that is intended and not an unwanted rendering.