Well I have discovered that I was using a method to QUIT the program that was not allowed.
Thanks to Corona688 for putting me straight and using the correct method to quit now.
This was apparantly a major bug in bash and was in there until at least bash version 4.3.42.

When tested on bash 4.4.5 the bash bug had been removed and created a bug in the code, it is now cured.

There are two separate closedown modes available now:-

'QUIT<CR>' that quits, saving all four of the AudioScope files saved inside '$HOME'.
'EXIT<CR>' that literally exits without saving those files.

It has come to my attention that some terminals are NOT 80 x 24 or 25 from a default install.
In fact one comes in at 77 x 23, one wonders why? After all it is NOT a classic AMIGA which does have that sized CLI.

Well I have had to use this terminal escape code to correct to the size for AudioScope.sh "\x1B[8;24;80t" to force a size increase.
The original size is saved as stty size and the values used to reset the terminal size back to default state on 'QUIT' or 'EXIT'.
Of course this method might be subject to some terminals not responding to the escape codes so manual resizing will be needed.

The four images are a sung note, the spectrum up to 4KHz of said note, the 'QUIT' window and 'EXIT' window.
(Note: the absolute paths are created through "$HOME"/path../file .)

RMS code for fixed waveforms is done but not incorporated in this version.

Stats so far:-

# Total Lines=5128.
# Blank Lines=46.
# Code Lines=2356.
# Comments=2726, (including the builtin Manual).
# Filesize=221113 bytes.

Enjoy...

Again thanks to Corona688 for his input.