In all systems of tuning, every pitch may be derived from its relationship to a chosen fixed pitch, which is usually A440, the note A above middle C (261.626 Hz). Note that for a classical piano and musical theory, the middle C is usually labelled as C4 (as in scientific pitch notation); However, in the MIDI standard definition (like the one used in Apple's GarageBand), this middle C (261.626 Hz) is labelled C3. In practice, a MIDI software can label middle C (261.626 Hz) as C3-C5, which can cause confusions, especially for beginners.