Fig. 4. Influence of the filtering applied to the synthetic waveforms on the apparent splitting parameters. Waveforms are simulated in a 2-layer model developed for station HRV (see Table 2). Apparent splitting parameters measured from waveforms with an upper spectral limits of 0.45Hz (bold), 0.35Hz (solid) and 0.15Hz (dotted) are shown, with a lower limit of 0.05Hz common for all. For all cases tested the estimate of the apparent fast direction tends to vary greatly when the delay is the smallest. The lowest bandpass (0.15Hz) gives most unstable results throughout. (Postscript version)