ETD Unisons was something else

[Robert Scott]

Kent Swafford wrote:

 >To me, these comments from Dean and Robert suggest another reason why
 >ETD-tuning of unisons may be unreliable -- if more than one frequency is
 >present at the partial level at which the ETD is listening, be it from a
 >wild string or from two different mis-tuned strings, the effect on the ETD
 >display is somewhat unpredictable and the display is somewhat unreliable. In
 >other words, although unisons made up of very clean-sounding strings may
 >sound find when the three strings are carefully tuned separately to an ETD,
 >false-beating and mis-tuned unisons clearly can "fool" an ETD.

Right.  If you are going to use an ETD to tune unisons, you really
should move the mutes and tune each string in isolation.  That's a
lot a mute moving, which takes time.  And if the center string should
happen to fall slightly after you set it to the ETD, aural unison
tuning would at least match the other strings to the center string and
give you a clean unison, which is more important than having the
absolute pitch of the note match the ETD.

On the other hand, the comment about false beats and beating
unisons fooling the ETD's phase display does not apply to a
frequency spectrum display, such as the one found in TuneLab.
(Both the SAT lights and the RCT spinner are phase displays.)
A frequency spectrum display does not attempt to resolve the
sound into a single pitch.  Instead it simply shows the raw
spectrum data with all the various frequency peaks included.
When you look at a spectrum display of a mis-tuned unison,
you see two separate peaks in the graph - one for each string.
As the unison is tuned, one of the peaks will move toward
and combine with the other peak.  The resolution of the spectrum
display in the low and mid-range of the piano is not as good
as the phase display, which is why TuneLab offers both a
phase display and a spectrum display.  But in the highest
octave, the resolution of the spectrum display is on a par with
that of the phase display.  So it is not out of the question to
tune unisons without mutes in the high treble using a spectrum display.
I'm not recommending it, but I have heard of it being done.

-Robert Scott
  Real-Time Specialties