[pianotech] ETD stretch vs pure (octaves)

Ron Koval drwoodwind at hotmail.com
Fri Nov 13 11:49:36 MST 2009



Duaine - interesting question that leads to a lot of other areas 
to discuss.  "pure" octaves actually have a bit of latitude.  That
is, depending on the piano, you can move one note of the octave around
and have it still sound pure in the "whole tone" approach to tuning.
Other pianos sit on the razor's edge between sounding ok and just bad.
 
What's the difference?  The matching of the specific partials between
the two notes.  Sometimes everything lines up pretty well and the 
octave has room to be expanded or contracted a bit.  Other scales find
the partials so divergent that the best you can do is to find the 
"least bad" sounding octave!
 
While the ETDs allow for a "push button" approach to choosing octave
width up and down the piano, the aural tuner chooses the octave width
based on the chosen test intervals which highlight specific partial
matches.  Many times, the best choice is not to make any one partial
match pure, but find a good compromise between all of the sounding
partials.  Room acoustics, brightness of the instruments and personal
preference lead to different tuning choices from bottom to top of 
the piano.
 
Ron Koval
chicagoland 		 	   		  
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