Max power is 32768 not 2048. You can verify it at https://webaudio.github.io/web-audio-api/#widl-AnalyserNode-fftSize - 'This must be a power of two in the range 32 to 32768, otherwise an IndexSizeError exception must be thrown.'

The size of the FFT used for frequency-domain analysis. This must be a power of two in the range 32 to 32768, otherwise an IndexSizeError exception must be thrown. The default value is 2048. Note that large FFT sizes can be costly to compute.