As of 2021-11, we are still far away from being able to clean up the
implementation of audio tones in our handset UI fw: before we can clean up the
implementation of audio tones, we will first need to detangle the wrong-minded
coupling between these audio tones and the buzzer, and that detangling will
require a development platform with a working buzzer, which means FC Venus.

However, we can apply a band-aid fix to the current misdesigned Condat audio
driver that would allow keybeep tones to be re-enabled on FC Luna with FC-HDS4
without being brutal on the developer-operator's ears: we can change the dBfs
amplitudes baked into F_xxx defined constants, and we can conditionalize this
change on CONFIG_TARGET_LUNA.  With this method we are constrained to picking
just one amplitude for the 3 different tones based on F_425 (busy, CW and
ringing) and likewise the same amplitude between the half-tone of keybeep and
the low tone of DTMF - but we are not seeking fully optimal tuning here, only a
band-aid fix to protect the developer-operator's hearing.

The set of shell scripts contained in this directory was put together to
facilitate easier experimentation with different amplitudes, easier than
entering full AT@TONE commands manually.

Amplitude selections being made for now:

Keybeep-half and DTMF-low: -26 dBfs
DTMF-high: -24 dBfs
F_425 tones: -21 dBfs