Midi files S.O.S.

[Rodolfo Medina <rodolfo.medina@gmail.com>]

Hi, listers.

I'm looking for a program that allows to modify
midi files, i.e. adjust tone and speed and cancel
traces: they're called midi sequencers, aren't they?
Well, I've been trying:

brahms
timidity
rosegarden
amarok
audacity
muse

, but none of them will help:
timidity seems to work, but it's not a sequencer:
it plays midi files fine but cannot modify them (is that true?);
the others don't even play midi files.

Anyone out there who can provide a hint?
What program to use, and how to make it work?

Thanks in advance,
Rodolfo