A Note on Low-Pass Filters for Retrieving Sampled Speech Signals
Henry S. McDonald · The Journal of the Acoustical Society of America · 1959
In the case of retrieving a sampled speech signal using a nonideal low-pass filter, some loss of quality is observed due to passing energy grouped as side bands about the sampling frequency. This paper describes a series of experiments designed to relate the filter characteristic to the speech quality. By subjective matching of signals using filters with variable out-of-band transmission, it was found that the transmission in the vicinity of the sampling rate was the most important correlate to signal distortion. The transmission in the frequency region adjacent to the base band was found to be relatively unimportant. An explanation in terms of the spectral characteristic of speech signals is offered. Presampling low-pass filtering was also investigated and found to be much less important than accurate post sampling filtering.