[CAUT] ghost tuning

[Fred Sturm]

On May 5, 2009, at 9:54 PM, David Love wrote:

> If you’re testing a 6:3 octave (for example) then you would hold  
> down C1 and C2 so that the dampers are lifted off the strings but  
> the hammers don’t actually strike the strings.  Hold down mute, it’s  
> called, and then strike (not hold down), strike and let go of the G3.

	I like to do a variant of this: play the octave softly, then strike  
the ghost tone in a staccato blow a tiny moment later. Getting the  
strings of the octave moving a bit to start with can make it easier to  
hear the partial beat. I like to accentuate a number of partial  
matches: with C1/C2 sounding, play C3 (4:2), G3 (6:3), C4 (8:4), E4  
(10:5), G4 (12:6), A# 4 (14:7) (each of these separately).  Listen to  
the difference in beat rates, it will tell you a lot about the  
inharmonicity curves of the two notes of the octave (how they line up  
or don't line up), and give a good idea of where to place that octave.  
Slightly wide 6:3 is a good default beginning place. If going up the  
ladder to 8:4 or higher isn't that far away, then a wider octave might  
be appropriate. Doing the whole ladder is also good ear training, and  
tells you a lot about what the "whole sound" of the octave will be.  
When those beat rates vary a lot, the "whole sound" will be pretty  
chaotic, and you have found out why.
	There is another way the term ghosting is used, and that is to  
accentuate test intervals. In that case, you would - to check 6:3 of  
C1/C2 - hold C1D#1 and strike G3, then hold D#1C2 and strike G3, and  
compare beat rates. Sometimes it is hard to hear the partials of the  
test intervals clearly, and ghosting can bring them to the fore.
	A caveat: ghosting can also accentuate higher partials. The test for  
6:3 can excite 12:6 as well. The test for 4:2 can excite 8:4 and 12:6.  
(The test note being struck has more partials than just its first  
partial, so it can excite the equivalents of those partials as well).  
So you need to be listening to beats at a specific pitch to get good  
information. It is also possible to use the ETD to look at the same  
information, setting the ETD for the partial you want to hone in on.  
This can be cumbersome, though, for a lot of the partials, depending  
on the model of ETD and what partial it is set to listen to in its  
tuning mode.
Regards,
Fred Sturm
University of New Mexico
fssturm at unm.edu


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