Inaccurate partial changes in tunings can create problems.
When using any computerized tuning system software, partial change errors are common. Sometimes they can be large enough to easily cause audible ‘hiccups’ in the tuning.
Some systems have as many as 4, 5, or even 6 partial changes built into them The most audible problems are heard in the lower half of the piano.
If the errors are less than 0.3 cents or so, they are insignificant. But partial change errors of .5 cents or more can easily be heard and create ‘hiccups’ in the tuning.
Inaccurate partial changes combined with the scaling challenges in the lower half are what cause many tuners to turn off their machines and tune aural only.
Almost any tuning system’s software will work on a long scale piano, but on the shorter scales, the combined effect of scaling issues and the partial change errors, can cause the software to not work very well at all in the bass and mid range Particularly on small grands, consoles, and spinets.
Only after the partial changes have been corrected, can an accurate stretch be determined. Simply increasing or decreasing the ‘stretch’ is not a fix.
Transitioning from plain wire to wound strings, and going from long bridge to bass bridge, is a challenge for both designer and tuner.
Scaling issues are often made worse by partial change errors.
Many highly regarded technicians turn off their ETDs for bass tuning. Their software just doesn’t work very well in the bass.
Some tuning software tries to remedy the scaling issues by allowing the technician to enter the locations of the bridge break and the plain wire to wound string break into their software before the tuning is ‘calculated’. This may improve their results a little, but it’s still a ‘guess’ as to exactly what is going on at the pianos’ scaling breaks and the software’s partial changes.
Some years ago, when talking with Al Sanderson about the potential problem at the tenor partial change, Al asked me with a smile, “Did I get any of them right?”. I answered, “Yes!”. Al knew, there was no way he or anyone else could get it right on every piano. He always said our job was to tweak the tuning aurally to compensate for all those things that the computer couldn’t catch.
Only after the partial changes have been addressed can a real solution be found as to how to best deal with the scaling issues.