A bandwidth extension encoder (100; 300) for encoding an audio signal, the audio signal comprising a low frequency signal comprising a core frequency band and a high frequency signal comprising an upper frequency band, the encoder (100; 300) comprising: a signal analyzer for analyzing the audio signal, the audio signal having a block of audio samples, the block having a specified length in time, wherein the signal analyzer is configured for determining, from a plurality of analysis windows, an analysis window to be used for performing a bandwidth extension in a bandwidth extension decoder; a core encoder for encoding the low frequency signal to obtain an encoded low frequency signal; and a parameter calculator (130; 320) for calculating bandwidth extension parameters (131; 321-2) from the high frequency signal, the bandwidth extension encoder further comprising a window controller for providing window control information indicating a plurality of analysis window functions, the parameter calculator comprising a windower controlled by the window controller, wherein the windower is configured to apply the plurality of analysis window functions and an analysis window function to be selected by a comparator to the high frequency signal, the signal analyzer comprising a patch module, which is configured to generate a plurality of patched signals based on the low frequency signal, the window control information and BWE parameters, wherein the patched signals comprise upper frequency bands generated from the core frequency band; a comparator which is configured to determine a plurality of comparison parameters based on a comparison of the patched signals and a reference signal being the audio signal or a signal (101-4; 101-2) derived from the audio signal, wherein the plurality of comparison parameters corresponds to the plurality of analysis window functions, and wherein the comparator is furthermore configured to provide a window indication corresponding to an analysis window function for which a comparison parameter satisfies a predetermined condition; and an output interface for providing an encoded audio signal, the encoded audio signal comprising the window indication. a signal analyzer for analyzing the audio signal, the audio signal having a block of audio samples, the block having a specified length in time, wherein the signal analyzer is configured for determining, from a plurality of analysis windows, an analysis window to be used for performing a bandwidth extension in a bandwidth extension decoder; a core encoder for encoding the low frequency signal to obtain an encoded low frequency signal; and a parameter calculator (130; 320) for calculating bandwidth extension parameters (131; 321-2) from the high frequency signal, the bandwidth extension encoder further comprising a window controller for providing window control information indicating a plurality of analysis window functions, the parameter calculator comprising a windower controlled by the window controller, wherein the windower is configured to apply the plurality of analysis window functions and an analysis window function to be selected by a comparator to the high frequency signal, the signal analyzer comprising a patch module, which is configured to generate a plurality of patched signals based on the low frequency signal, the window control information and BWE parameters, wherein the patched signals comprise upper frequency bands generated from the core frequency band; a comparator which is configured to determine a plurality of comparison parameters based on a comparison of the patched signals and a reference signal being the audio signal or a signal (101-4; 101-2) derived from the audio signal, wherein the plurality of comparison parameters corresponds to the plurality of analysis window functions, and wherein the comparator is furthermore configured to provide a window indication corresponding to an analysis window function for which a comparison parameter satisfies a predetermined condition; and an output interface for providing an encoded audio signal, the encoded audio signal comprising the window indication.