Cracking the unisons

[Greg Graham]

I'm hoping someone will take a stab at a detailed
definition of "Cracking The Unisons".  

I've checked the archives, and lots of people mention
Virgil Smith's technique, some claim to use it, only a
few have partially described it, and I suspect I'm
still not getting it.
  
As I understand it:  If a three-string unison is found
to be slightly flat or sharp compared to a test
interval or two, you adjust the first string without
muting the other two, then adjust the remaining
strings to clean up the unison.  

Reasons for doing this:  It's faster than messing with
mutes, it produces better unisons, it avoids the
"Virgil Smith Phenomenon" of a unison going flat when
all three strings are vibrating compared to a single
string of the unison by itself.  (Please, let's not
debate the phenomenon.  I'm just asking about
cracking.)

Is this all there is to the technique?  I presume the
hard part is being able to hear the beat clear up on
the 2nd string while the 3rd is still beating away,
akin to dealing with false beats.

Some of the unanswered questions (in my mind):  

1.  How big an adjustment to the unison are we making
when using the cracking technique?  One BPS? Half a
beat? One beat in 15 seconds?    

2.  Do we move the 1st string to create a beat rate
matching the out-of-tuneness of the unacceptable test
interval, or is there some other method at work?  If
the 5th is beating about 1/2 BPS too fast, do we
create a 1/2 BPS unison, then move the other two
strings to eliminate the beat?  

3.  The single vs. three string pitch change "Virgil
Smith Phenomenon": How big a change are we talking
about?  I've read 0.1 to 0.3 cents.  

How close is "close enough"?  I know I'm not yet good
enough to hear some of these small errors in unison
tuning.  I don't know if I could tune two strings to
0.25 cents accuracy while the third was 1.0 cent out. 
Heck, who am I kidding?  Sometimes I don't hear the 1
cent error, especially in upper octaves.  0.25 cents
mid keyboard is about one beat in 16 seconds, right? 
Is that the kind of accuracy we are talking about
here?

I need to see and hear this demonstrated someday, but
I'm hoping someone on the list who is a "crack addict"
can help me with a better written description.  The
archives need clarification, as do my unisons.

Thanks, 

Greg Graham
Brodheadsville, PA
One tuning exam (and several months) away from
RPT-dom.




		
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