Observed gravity anomalies are the sum of all the underground effects. To find basement topography we usually divide the Bouguer anomalies into residual and regional parts via separation procedure. Low frequency (i.e. long wavelength) content belonging to deep effects including the variations in the Moho and Lithosphere-Asthenosphere Boundaries.
Different kind of filtering give different results. More importantly, is to find an ideal cut-off frequency. Our calculation shows that there is up to 2 km difference in the depth while the data fits are fairly the same. The difference between three cutoff wavelengths in 15 models, which all produce the same data fit, shows about 25% variation in the final depth of the basement.
An alternative to separation via filtering the data is to use independent measurements of lateral depth variations of underlying boundaries to calculate their Bouguer signature, which then can be subtracted from the observed data prior to calculations.