There is a correlation between the Frequency bands (FFT size) parameter and the frame length. The frame length will be cropped or padded to the Frequency bands value while applying the FFT. For example, with a 8kHz sampling frequency and a time frame of 0.02s, each time frame contains 160 samples (8k * 0.02). If your FFT size is set 128, time frames will be cropped to 128 samples. If your FFT size is set to 256, time frames will be padded with zeros.