A character string denoting the filter type. Supported types include: EXTREMAL PHASE (daublet): haar, d2, d4, d6, d8, d10, d12, d14, d16, d18, d20
LEAST ASYMMETRIC (symmlet): s2, s4, s6, s8, s10, s12, s14, s16, s18, s20
BEST LOCALIZED: l2, l4, l6, l14, l18, l20
COIFLET: c6, c12, c18, c24, c30
Default: s8.