Ableton's live digital audio workstation allows you to configure nearly any parameter, including the key and time signatures. The key signature determines which notes the software plays; for example, a C Major key signature consists of only natural notes -- that is, no sharps or flats -- while a G Major scale raises the F natural to F sharp. The time signature determines the rhythm of the music: the first value in the time signature tells Ableton how many beats are in each bar, while the second value determines what note length Ableton should consider to be a beat.
Launch Ableton and open a project. Click on a MIDI track within the project.
Click the "Live Devices" icon at the far left of the program window. Click the arrow next to "MIDI Effects" to expand it. Click the arrow next to "Scale" to open the "Scales" section. Ableton includes a variety of built-in key signatures, including minor, major, pentatonic and whole tone.
Click a key signature -- "C Major," for example -- and drag it onto the MIDI track. Click and drag the "Base" knob to choose a key signature.
Start Ableton and open a project.
Click the first number in the "Time Signature" box in the top-left corner of the Ableton window. Type in a new value; for example, if you're planning to compose music in 3/4 time, type in "3."
Click the second number in the "Time Signature" box. Type in a new value. Click anywhere outside the "Time Signature" box to set the new time signature.
If you want to use a flat key signature, set the "Base" knob to its equivalent sharp key signature. For example, set the "Base" to "A#" to get a B Flat signature.
If you change the time signature in a set, you must manually change any previously-created tracks to the new time signature.