Timidity is a little commandline program to play midi files on Linux:

timidity Was-soll-das-bedeuten.midi

My midi is a choir score with three voices and the output of timidity looks like this:

Playing Was-soll-das-bedeuten.midi
MIDI file: Was-soll-das-bedeuten.midi
Format: 1  Tracks: 6  Divisions: 384
Sequence: control track
Text: creator: 
Text: GNU LilyPond 2.18.2           
Track name: :Soprano
Track name: :Alto
Track name: :Men

With the above standard command all voices are played together. To practice something it is sometimes nice to have only your own voice alone, you can do this by quieting/muting all voices except your own. The voices to be muted are listed after the option -Q separated by comma. The value 0 means all voices, the number of the other voices is given by their order in the output. So in the file I have, Soprano would be 1, Alto 2 and the men’s voices 3. Including the number mutes the voice, including it with a minus sign plays it. So let’s say I want to practice the alto voice, I’ll mute all but voice 2:

timidity -Q 0,-2 Was-soll-das-bedeuten.midi

It’s also simple to transpose stuff, this will play the song two semitones higher:

timidity -K 2 Was-soll-das-bedeuten.midi