When to Use Weighted Overlap-Add

Synthesis windows are not used in simple FFT convolution processors using the OLA method, since the input frames are supposed to be expanded by the convolution, and the synthesis window would ``pinch off'' the ``filter ringing'', yielding the wrong results.

Synthesis windows can be used in conjunction with spectral modifications made by means of the ``filter bank summation'' (FBS) method, which is the subject of the next lecture.

Synthesis windows are appropriate for erstwhile ``instantaneous'' spectral modifications, such as

• spectral quantization (compression),
• frequency scaling (time-scale modification), or
• ``memoryless'' spectral nonlinearities.

In other words, whenever samples outside of the original signal time frame are considered processing artifacts, use of a synthesis window will eliminate them.