TL97 - How I use it

[Frank Weston]

How I use TL97 (Part 1.  How to develop a stretch curve for the unwound
strings)

The strength of  TL97 is that it presents a wealth of information which
allows a knowledgeable tuner to make good choices in developing a tuning
for any piano.  TL97 will not automatically measure a piano and generate a
tuning for the user.  Some view this as a handicap.  I do not.

Before you use TL97 for the first time, check the pitch measured by TL97
against a known accurate source.   If the crystal in PC soundcard is not
quite standard, you may have to use a simple calibration program which is
provided with TL97 software.  You should only have to do this once for each
computer on which you use TL97.  Don't rely on your tuning fork as an
accurate source unless you have calibrated it carefully.   Also, get a good
external mike for your  laptop.  Most internal mikes will give poor results
in the low bass, and possibly in the high treble.

Developing a good tuning from scratch starts with taking inharmonicity
measurements.  If the piano is not close to pitch, tune one string on the
unisons to be measured to pitch.  Mute the remaining strings on the unison
and measure inharmonicity on only the one tuned string.  While TL97 can
measure and display inharmonicity on bass strings, I have found that the
partials to which each bass string is tuned vary so wildly that it is
quicker to tune wound strings by ear unless a big pitch raise is called
for.  In that case, assume a smooth curve for the bass for the pitch raise,
and then on fine tuning go by ear.  To make things simple for generating
tuning for unwound strings, enter the numeric editor, and select the second
partial  as the partial for tuning on the lowest unwound note and for all
notes up to C3 (C3 already uses the second partial by default).

Measure the lowest unwound note, C3, C4, C5, C6, and C7. With this
inharmonicity information enter the graphic editor.  In the graphic editor,
the user can select all sorts of options for tuning: single octaves 2/1,
4/2, 6/3, 8/4, 10/5, 12/6; double octaves 4/1, 8/2, 12/3; triple octaves,
and all sorts of other intervals.  To keep things simple, choose to tune
single octaves 2/1.  THERE ARE MANY MORE WAYS TO DEVELOP A STRETCH TUNING. 
 THIS IS JUST ONE SIMPLE EXAMPLE.  Also select to display inharmonicity at
the breaks.  What this function does is display the discontinuity in the
inharmonicity curve caused by a change in the measured partial.  By
default, TL measures the second partial below C4, the fourth partial below
C3 (we extended the second partial down to the lowest unwound for
simplicity), and higher partials at subsequent lower notes. 

The graphic editor can be confusing, but once you work with it a little,
you will find it to be quite functional.  The general idea is to select an
anchor note or notes, then using an editing tool, modify the stretch on a
range of notes extending from the anchor note(s).  I could write a whole
instruction manual on how to use the graphic editor, but I will not.  Use
it, experiment, spend some time to learn how it works.  If you have
specific questions ask.   (Don't ask me, write Bob Scott). 

To easily develop a stretch curve for the unwound strings, make C4 the
anchor note, then use the linear modify tool to move the section of the
tuning curve between C4 and C5 so that the single octave 2/1 partial which
is displayed in red.  Now make C5 the anchor note and move the section of
curve between C5 and C6 so that the partial matches.  Continue upward in
like fashion all the way to C8.  If the curve goes off the display, use the
zoom back function to make the whole curve visible.  Now select the
quadratic modify tool.  Use the left mouse button to make C4 and C5 the
anchor notes, then fair the curve between these notes.  Select C5 and C6,
and fair that section of curve.  Continue all the way to C8.  You should
now have a smooth tuning curve with reasonable stretch from C4 to C8.

Now, make C4 the anchor note.  Use the break modify tool to move the curve
below C4 up (or down) so that B3 butts against the inharmonicity at the
break indicated in red above C4.  Select the linear modify tool and move
the curve from B3 to C3 and from C3 to lowest unwound so that the curve
matches measured inharmonicity and/or the green guidelines which represent
a beatless match for notes tuned to the second partial from lowest unwound
to  C3 to C4 to notes above C4 tuned to the fundamental.   If inharmonicity
measurements are taken all the way to A0, the break modify tool can be used
at each break in the partials selected for measurement, and the curve
modified as described above.  Since we didn't measure notes below  the
lowest unwound, stop here.

Now select the shift entire curve tool and move the whole curve up or down
as required to make the offset of A4 equal zero. 

The whole process of measuring and graphically editing a tuning for the
unwound strings should take about five minutes.  Once you are done, this
tuning can be stored and used at any time in the future.

The next step is to tune the piano using the tuning you have developed. 
I'll discuss that in another post if there is enough interest.

Frank Weston