An apparatus (130, 130A, 110) for encoding an audio signal comprising a plurality of frames, the apparatus comprising: a modulated lapped transform tool for transforming a time domain, TD, representation of the audio signal, or a processed version thereof, into a frequency domain, FD, representation, the modulated lapped transform tool being configured to perform a modulated lapped transform analysis using an analysis windowing function (40, 50, 70, 240) having a crossing portion (44, 64, 244) crossing a linear function (40', 240') in correspondence of at least four points (#1, #2, #3, #4); and a bitstream writer configured to prepare a bitstream based on the FD representation of the audio signal or a processed version thereof, wherein the analysis windowing function is defined so as to be asymmetric, wherein the analysis windowing function (40, 240) is defined so as to be, in the crossing portion (44, 94, 244): greater than the linear function (40', 240') in a first interval (41,241) between a first crossing point (#1) and a second crossing point (#2); lower than the linear function (40', 240') in a second interval (42, 242) between the second crossing point (#2) and a third crossing point (#3); greater than the linear function (40', 240') in a third interval (43, 243) between the third crossing point (#3) and a fourth crossing point (#4), wherein the analysis windowing function is defined so that the absolute maximum value (41', 241') is in one of the first and third interval, characterized in that the linear function (40, 240) is a constant function with constant value 1. a modulated lapped transform tool for transforming a time domain, TD, representation of the audio signal, or a processed version thereof, into a frequency domain, FD, representation, the modulated lapped transform tool being configured to perform a modulated lapped transform analysis using an analysis windowing function (40, 50, 70, 240) having a crossing portion (44, 64, 244) crossing a linear function (40', 240') in correspondence of at least four points (#1, #2, #3, #4); and a bitstream writer configured to prepare a bitstream based on the FD representation of the audio signal or a processed version thereof, wherein the analysis windowing function is defined so as to be asymmetric, wherein the analysis windowing function (40, 240) is defined so as to be, in the crossing portion (44, 94, 244): greater than the linear function (40', 240') in a first interval (41,241) between a first crossing point (#1) and a second crossing point (#2); lower than the linear function (40', 240') in a second interval (42, 242) between the second crossing point (#2) and a third crossing point (#3); greater than the linear function (40', 240') in a third interval (43, 243) between the third crossing point (#3) and a fourth crossing point (#4), greater than the linear function (40', 240') in a first interval (41,241) between a first crossing point (#1) and a second crossing point (#2); lower than the linear function (40', 240') in a second interval (42, 242) between the second crossing point (#2) and a third crossing point (#3); greater than the linear function (40', 240') in a third interval (43, 243) between the third crossing point (#3) and a fourth crossing point (#4), wherein the analysis windowing function is defined so that the absolute maximum value (41', 241') is in one of the first and third interval, characterized in that the linear function (40, 240) is a constant function with constant value 1.