STFT constructor
      
      STFT(
    
- int chunkSize, [
- Float64List? _win
Constructs an STFT object of the given size, with an optional windowing function.
Implementation
STFT(int chunkSize, [this._win])
    : _fft = FFT(chunkSize),
      _chunk = Float64x2List(chunkSize) {
  if (_win != null && _win!.length != chunkSize) {
    throw ArgumentError(
      'Window must have the same length as the chunk size.',
      '_win',
    );
  }
}