H9 Looper Audio Crossfades

[brock]

From another thread: wedelich:

Thanks guys, good suggestions!  

Regarding the punch record to make stutter loops.  You should be able to do this with punch dubbing.  Just record an initial silent section, play the silent loop, then quickly step on and off the left footswitch to dub (make sure it's in PUNCH mode).  This should give you some good stutters. 

This question revolves around recording "seamless" sustaining loops.  I've been fading in sustained notes / chords with an EHX Freeze.  I've tried this with the initial Record loop, and also the Dub-over-silence method above.

There does appear to be an "attack' in level at the loop start.  More so than a zero-crossing 'pop' would present (although I hear those kinds of artifacts on repeated Play switch presses, too).  I haven't had the chance to check if MIDI Start control has the same behavior.

What seems strange is that the first press of the Play switch appears to crossfade the recorded loop in.  Subsequent presses do not.  It may have to do with restarting the loop from some random playback position.  I have tried adjusting the Ply-Start and Ply-Length to find a sweet spot without a seam (no luck so far).

The "seams" can be cool effects in their own right, but I'm wondering if there could be a way around the noticeable transitions (when desired).  I can disguise them somewhat with initial Play, post-reverb, and Playmode – Once (then repeat the process).  Any insights?

[wedelich]

Hi brock, 

Well, the head/tail crossfade that we use for seamless dubbing over the splice (and smoother transitions overall) is always running, so that's what you're hearing in the initial Press of the play button, except the fade down part of the loop tail is of course muted for initial play, so you just get a quick fade up.  I think the crossfade is something like 5 ms for non-tempo mode, and 20 ms for tempo mode (to account for external MIDICLK jitter/noise). 

The whole point of this method was to allow continuous reverb type sounds to dub over the loop boundary without any audible seam.  The previous TF Looper always did a quick fade down then back up (not even a crossfade), so it wasn't capable of this at all.  I didn't come up with anything other than this fade for initial transitions to Play though….. I suppose the best thing you could do for Record to Play transitions is actually transition from Record to Dub instead.  Then turn off Dubbing after fading your input signal down.  

The clicks on multiple play-retriggers sounds like a bug to me, nothing is supposed to click or pop with the Looper….. we wanted it to be as smooth as possible.    

There may be some more sophisticated DSP tricks that we could employ in the future for these initial Play transitions, like running a zero crossing detector and always starting close to zero crossing, but I'm just spit-balling really, because I'm probably not going to do anything like that in near future. 

[brock]

Thanks for the depth of detail in your response.  All of that comes in handy with drilling down into the deeper aspects.  I tend to push my gear to the limits to squeeze out unusual but useful techniques.

Quote:

I suppose the best thing you could do for Record to Play transitions is actually transition from Record to Dub instead.  Then turn off Dubbing after fading your input signal down.

Appreciated; that works well.  Double-click Record in H9 Control; triple-tap LFSW on the pedal … No doubt this will become more easily accessible & intuitive as I put the finishing touches my MIDI pedal Looper template.  You guys did a great job with this algorithm.  The amount of effort put into it shows (special thanks for the rock-solid sync).

Quote:

The clicks on multiple play-retriggers sounds like a bug to me, nothing is supposed to click or pop with the Looper….. we wanted it to be as smooth as possible.

Well, if no one else is reporting this behavior, it could very well be system-specific (admittedly, a complex routing here).  I first noticed it with the continuous audio seamless looping.  It's harder to determine when Loop Start begins with a guitar note's typical envelope (pick attack).  I'll experiment some more with keyboard sources, different loop types, and repeated Play retriggers to see if there's a real recipe.

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