(57) To synthesize transient sounds a time-varying recursive filter (20) is used in which
the multipliers (57) following successive delay elements (59) ofthe filter have sets
of normalized covariance matrix coefficients (b) which are stored (54) and which have
been obtained from the normalized autocorrelation coefficients (a) for each of a plurality
of time frames (11) of a sampled transient sound signal which is to be synthesized
from the stored coefficients. The normalization constant (A) during a frame is also
applied as a scale factor (A) to the recursive filter. A pseudo-random noise generator
(51) supplies the input signal to the recursive filter (20) at the sample rate, which
is the rate of a clock pulse generator (52) triggering the noise generator (51). A
plurality of successive time frames determined by cascaded delays (59) in the recursive
filter and a set of coefficients for each time frame provides the entire synthesized
transient signal. The respective sets of coefficients (A, b, to bm) are supplied from a store (54) synchronised from the clock pulse generator (52)
through a modulo F counter (53) where (F) is the number of samples in a time frame.
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