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Alternate Tuning Vs. Virtual Capo


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#1 bwnichols

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Posted 06 November 2013 - 04:17 AM

So I’ve been working with a set of three ‘spider’ capos that can capo individual strings.

 

Essentially I set the root chord (usually, but not always) of the key as the open strum with the capos, and play rest of chords normally but up the neck – so all transitions to the capo’d chord are ‘nails’ – fast and clean.  Plus it give my hand a break, so I can play for hours without ‘claw-cramping’.

 

Now envision picking over the top of that open strum … it sounds pretty cool, like rhythm and lead combined.  But I can’t change the chord quickly AND the tuning needs tweaking whenever the capo settings are changed.

 

What I wish I could do is control (i.e. change) that capo’d chord fast and clean via a foot-operated effects board.  Then I read about some MIDI guitars where actual string tuning doesn’t even matter – and bingo, I realized what I want to do can be done via software and signal-processing only. 

 

But there's problem I see from the 'virtual capo' product description and the Line6 video tutorials I've watched, namely that unless a 'bar' capo is modeled, the 'virtual capo' feature changes the tonal distance between strings -- OK fine if alternate tuning is what you want, but suppose you really don't want to relearn all those 55545 tonal spacing riffs, scales and chords that you already know?

 

Does the Workbench allow for development of individually capo'd strings, maintaining the stanard tonal distance between strings?  What I would call a 'true virtual capo'.

 

Thanks in advance...and regardless of the answer, I'll be headed down to my local Guitar Center to check-out these very cool-looking instruments very soon!


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#2 Rewolf48

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Posted 06 November 2013 - 05:45 AM

Virtual capo changes the open tuning of the guitar.  Which is the most common requirement - so it is almost instant for playing in Drop D or Eb (these are actually preset tunings on a JTV).

 

What you are asking for is that notes fretted above a certain point on each string play as normal, but that notes at or below that point sound as if they were fretted at that point.

 

This is an interesting idea (never seen let alone tried a Spider Capo), and one that could potentially be supported on a JTV through a software upgrade if Line 6 choose to try it.  But it isn't how it currently works. It would require that the tuning adjustment per string is dynamically changed (for fretted below the capo point) or switched off (for fretted at or above the capo point).

 

You could submit this as a suggestion on http://line6.ideascale.com/ but don't hold your breath waiting


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#3 bwnichols

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Posted 06 November 2013 - 12:35 PM

Thanks for your response, Wolf... 

 

For those not familiar with spider capos, and to illustrate that what I'm talking about is really very simple and not beyond the physics of normal guitars, here is my modest setup, capo'd for F-chord:

 

 

20131106_105042.jpg 20131106_105007.jpg

 

As the second photo shows, the 3rd fret can still be fingered if needed.  Simply set F, C, G, D, Dm, A, Am, B, E -- whatever you like, then play additional chords and notes in standard positions from the 3rd fret on up.  

 

Unlike many alternate tunings (see 'special case' exception below), chord shapes and scale patterns remain unchanged.

 

Which is not intended as a knock on the utility or appeal of alternate tunings, just simply to illustrate my hypothesis that in the general case, physics of alternate tunings vs capos is distinctly different.  

 

By inspection I think, these special cases are obviously equivalent:

  • An alternate tuning where the tension in all strings is changed by an equal amount (e.g. Eb 'blues tuning')
              
        is equivalent to
     
  • Applying a capo across all strings at the same fret. 

        ...regardless of whether the fret is physically above, or virtually (as with Eb tuning) below the nut.

In the general case however, tuning controls the tension of a string and therefore the tonal distance between strings, while capos control where a string is fretted regardless of tension. As the spider capos demonstrate, strings can be physically capo'd independently while leaving the tuning unchanged.

 

At this point perhaps a YouTube video is in order to demonstrate the usefulness and fun of this idea.  

 

But first I'll need to get my basement studio-pit tidied-up a bit... give me a week or two on that tall order, the maid's been on permanent vacation!


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#4 phil_m

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Posted 06 November 2013 - 01:08 PM

I understand what you're wanting, but I don't think it would ever be possible unless Line 6 changed the way they handle pitch shifting in the Variax in general. I don't believe the Variax is tracking absolute pitch when it does pitch shifting. All it's doing changing the pitch relative to note being picked up. For what you want to be possible, it would have to track absolute pitch in some way so it could differentiate between the note generated from an open string and a fretted one. I imagine Line doesn't do this simply because doing it would add latency.


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#5 bwnichols

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Posted 06 November 2013 - 02:42 PM

Thanks Phil, for your response...

 

Understand what your saying about differential vs. absolute pitch, but I really don't think absolute pitch tracking is necessary, and here's why:

 

Consider the tuning (i.e. tension) of any string, capo'd vs uncapo'd

  • Every note on the fretboard sounds exactly the same, above the capo'd fret.  The capo has no effect on, i.e. is 100% independent of, the tuning (tension1).
  • For any pitch equal to or below the stored value (capo'd pitch), play the stored value.  Just need a differential comparison of the fretted pitch to the stored value.

Seems to me all the signal-processing capability is there -- the hard part is going to be convincing anyone in a position of influence (or capability) that the software development (or demo hack) effort will be worthwhile.  

 

Planning to put some YouTube vids together, but it will be a few weeks...

 

In practical application, the capos do in fact change the string tension somewhat, sufficiently enough that I generally tune-up whenever changing the spider setup to a different chord.  Envision that Line6 real-time signal processing capability someday will eliminate this nuisance task, providing 'third-hand' real-time chord-changes via footbox, thus freeing the musician's left hand for freestylin'

 

 


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#6 phil_m

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Posted 06 November 2013 - 02:55 PM

For any pitch equal to or below the stored value (capo'd pitch), play the stored value.  Just need a differential comparison of the fretted pitch to the stored value.

 

 

Well, and I think that's the issue... There's no such comparison being made. The Variax isn't "listening" to the pitch of the note coming from the string in any way. It's just taking the pitch and shifting it by a certain amount. Now, there is some sort of technology for pitch detection in the current algorithm because it detects pitch when you set up a virtual capo. But I don't think it being used at all when the Variax is "live". The Variax is unlike other MIDI guitars in that regard. If your strings are out of tune while playing the Variax while using an alternate tuning, you'll be out of tune. There's no pitch correction going on.

 

I'm not saying it's impossible altogether. I'm just saying it would involve changing the way the pitch shifting works currently.


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#7 bwnichols

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Posted 08 November 2013 - 03:26 PM

Thanks Phil again for your response, I hear what you're saying and have given it some serious thought.

 

In the spirit of simplifying programming & signal-processing complexity, wouldn't it be acceptable to play (i.e. when fingered) ALL fretted notes -- below the capo, above and equal to?  So unlike a physically capo'd guitar, the entire fretboard of the virtually-capo'd guitar would be open for fingering?  That's the way JTV virtual capo essentially works now with respect to the fretboard, so the less change to the status quo generally the cheaper and simpler the implementation of a given change, yes?

 

So if we can agree this is acceptable, then the only condition for playing the stored (capo'd) value would be when the string is vibrating at its lowest (i.e. 'nut') frequency.  Now I'm not an analog signal guy, but enough of an engineer to know that a vibrating string can act as both a signal source and a filter capable of canceling itself out completely. 

 

Run two signals through an analog 'high & low-pass filter' where the threshold values for both high and low pass are set by the string's nut frequency:

  1. Input the string's vibrating frequency through the high pass, and
  2. the string's stored value through low-pass side of the filter.

Output either:

  1. The string's vibrating frequency above, or
  2. the string's stored value, equal to or below the threshold value.

Again, not a signal guy, but this seems like rudimentary electronics compared to what must be going on inside a JTV to provide its amazing capability...


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