Thank you js1 for your reply.
Using the S1 Tone Generator is a great idea which I'll try tomorrow. I did successfully use my Helix tuner today which kept me in tune with the band during four church services.
As stated in my original post, I downloaded a (Fender) tuner which also agreed with my Helix tuner.
So the issue is definitely within Studio One and is a mystery to me, because the tuner has flawlessly worked since 2010 when I first purchased Studio One Pro.
Over the years, I've read about a Preference or Setup file and wondered if somehow that's the issue but I haven't messed with that for years, so I doubt that's the case.
It took a while, but after doing a few experiments, I think this is all about the way you tune your guitar.
Based on the experiments I conducted, it appears that Tuner FX in Studio One 7.2.3 does
not work correctly when Mode is set to "Custom" and "Standard Guitar" is selected. When configured this way, Tuner FX produces garbage.
However, when Mode is set to "Chromatic", Tuner FX works
correctly.
EXPERIMENT
I added the Tuner FX in Studio One as in Insert on an Addictive Keys (XLN Audio) grand piano track and then configured Tuner FX correctly for use as an instrument tuner, in this case the instrument is a VSTi virtual instrument Grand Piano, which has been set to use "Concert A" (440-Hz) as its reference tuning pitch. I did another experiment with an electric guitar from SampleTank (IK Multimedia) with the same result.
Then I added music notation to play a series of whole notes, specifically A3 (220-Hz) and hit play to observe what the Tuner FX native Studio One effect control does.
For reference, previously I had tried different settings and left Tuner FX configured in the last way I tried, which reproduced the same incorrect behavior you experienced, including the Tuner FX "Difference" consistently showing "50 cents" with no variation.
Now it makes sense; and because the way Tuner FX was configured, the results were complete and total nonsense.
It was showing something, but what it was showing was illogical; and this led me to do a few more experiments to determine how Tuner FX works as an instrument tuner.
The attached image shows the correct way to configure Tuner FX to work as a guitar tuner; and it verifies that the Tuner FX in Studio One 7.2.3 (a) is working nicely and (b) is very accurate when configured this way.
However, when you set the Mode to "Custom" and then select "Standard Guitar", the Tuner FX shows nonsense; so from this I infer that it is
not working correctly and has a bug when configured this way.
Tuner FX works
correctly when the
Mode is set to "Chromatic" and
Strobe is "OFF".
Otherwise, it produces what looks to me to be garbage; hence is
not working correctly when Mode is set to "Custom" with "Standard Guitar" selected from the drop-down list.
[
NOTE: I had never used Tuner FX and mistakenly mapped it to another topic in the Lounge where the focus is on setting the reference tuning frequency for instruments, not on tuning instruments, per se. I thought Tuner FX was used the way a reference tuning frequency control is used in SampleTank and Opus to set the reference tuning pitch for a specific instrument; but apparently this is not what Tuner FX does. It looks like Tuner FX literally is a tool for tuning rather than setting the reference tuning tone; so my bad.
]
SUMMARY AND SOLUTION
There is a gnarly bug in Tuner FX in Studio One 7.2.3 when Mode is set to "Custom" and "Standard Guitar" is selected.
However, Tuner FX works correctly when
Mode is set to "Chromatic" and
"Strobe" is "OFF".
So the solution is to set Tuner FX as shown in the attached image.