[Harp-L] using compression

[Garry Hodgson <harp@xxxxxxxxxxx>]

i often hear (read) harp players here mention using compression
as part of their live sound, either using a dedicated pedal, an
effects box (digitech), or as a side effect of some other device.
so i thought i'd investigate.

when i use the compressor in audacity to postprocess music, the
available settings are threshold, ration, and attack time.  i more
or less understand how these work (attack time is a little fuzzy).

my digitech rp250 has Sustain, Tone/Attack, and Compressor Level.
the Tone/Attack controls Tone if using digitech compressor, or Attack
if emulating Boss CS-2.

so my questions are:

why do i want to use this?  what effect does it have on the sound,
specifically harp sound.  i understand compression in general.

how would you set those parameters for what type of effects?  would
you set things differently in different circumstances?

what effect, in harp context, does Attack have?  Sustain?

any other advice on using this would be appreciated.

thanks

--
Optimism and pessimism don't exist for me.
I'm a blues man.  I am a prisoner of hope.
I'm going to die full of hope.
- Cornel West