Using simple sinusoids as inputs, the Burg spectra are studied with a view to deciding the appropriate lengths of the prediction error filter (LPEF). It is observed that the higher the frequency (vis a vis the total data length representing the fundamental period), the lower the LPEF needed. In the case of mixed samples, frequencies exceeding the fifth harmonic are resolved with LPEF of about 50% (half-data length) and higher LPEF are likely to give spurious peaks. For lower frequencies, higher LPEF may be needed, sometimes even approaching 90% of the data length. Thus a mixed sample needs the study of Burg spectra from low as well as high LPEF simultaneously.