A processor for processing an audio signal (200), comprises: an analyzer (202) for deriving a window control signal (204) from the audio signal (200) indicating a change from a first asymmetric window (1400) to a second window (1402), or indicating a change from a third window (1450) to a fourth asymmetric window (1452), wherein the second window (1402) is shorter than the first window (1400), or wherein the third window (1450) is shorter than the fourth window (1452); a window constructor (206) for constructing the second window (1402) using a first overlap portion (800) of the first asymmetric window (1400), wherein the window constructor (206) is configured to determine a first overlap portion (1000) of the second window (1402) using a truncated first overlap portion of the first asymmetric window, or wherein the window constructor is configured to calculate a second overlap portion (1330) of the third window (1450) using a truncated second overlap portion (814) of the fourth asymmetric window (1452); and a windower (208) for applying the first and second windows or the third and fourth windows to obtain windowed audio signal portions (210).