If you want to edit music and sound files, Audacity is your best choice. It is a free, cross-platform program for recording and editing sounds.
It has many features. You can use it to: record live audio; convert tapes and records into digital recordings; cut, copy, splice, or mix sounds together, as well as, applying many filters, such as, changing the speed or pitch, adding echo or removing noise from a recording, etc.
On the other hand, Solfege “is an ear training program written to help you train intervals, chords, scales and rhythms”. It is also free software and part of the GNU Project.
Rosegarden is a free “music composition and editing environment based around a MIDI sequencer that features a rich understanding of music notation and includes basic support for digital audio”. It is only available for GNU/Linux.