Hi!
For a DAW to record: Try audacity (it's rather simple). I said rather. It means it is worthy to work with. For the big time work: go for ardour. There is a debian package for it, and I believe there should be a ubuntu package for it.
For sample-playback: If you don't have sampling libraries yet or if you want to go for others: there is linuxsampler, which can read gigasample version2 sounds. There is hydrogen for drum-sounds, which has its own libraries and lets you create new drum-libraries. there is alsofluidsynth (and qsynth for the graphical interface). Fluidsynth (qsynth respectively) read soundfonts. There are some very ok drum-libraries in SF2 format.
That's just completing to makr Knecht's message, not an either-or alternative.
Kindest regards
Julien
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Music was my first love and it will be my last (John Miles)
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