A frequency converter comprising a frequency transposition block for samples (11.sub.Q.sub._.sub.1, 11.sub.Q.sub._.sub.2), a filtering block (12.sub.Q.sub._.sub.1, 12.sub.Q.sub._.sub.2), the filtered samples y(n) verifying y(n)=c(0).Math.x(n)+c(1).Math.x(n−1)+c(2).Math.x(n−2)+ . . . +c(p−1).Math.x(n−p+1)+c(p).Math.x(n−p)+c(p−1).Math.x(n−p−1)+ . . . + . . . +c(1).Math.x(n−2.Math.p+1)+c(0).Math.x(n−2.Math.p), wherein x( ) are the transposed samples and c(0), . . . c(p) are the real coefficients of the filter; and being adapted for, during a cycle for determining the value of the filtered sample y(n): calculating the first terms c(0).Math.x(n), c(1).Math.x(n−1), c(2).Math.x(n−2), . . . , c(p).Math.x(n−p) by multiplying the respective coefficients and transposed samples, and storing in memory said first calculated terms; reading the second terms c(p−1).Math.x(n−p−1), . . . , c(1).Math.x(n−2.Math.p+1), c(0).Math.x(n−2.Math.p), calculated and stored in memory during previous cycles for determining the value of filtered samples y(n−m); and determining y(n) by summation of the first and second terms.

Filters are discussed where a first window function and a second window function are applied to a digital input signal, wherein a window length of the first window function is longer than a window length of the second window function. The results of this windowing are integrated.

Filters are discussed where a first window function and a second window function are applied to a digital input signal, wherein a window length of the first window function is longer than a window length of the second window function. The results of this windowing are integrated.

A frequency converter comprising a frequency transposition block for samples (11.sub.Q.sub._.sub.1, 11.sub.Q.sub._.sub.2), a filtering block (12.sub.Q.sub._.sub.1, 12.sub.Q.sub._.sub.2), the filtered samples y(n) verifying y(n)=c(0).Math.x(n)+c(1).Math.x(n1)+c(2).Math.x(n2)+ . . . +c(p1).Math.x(np+1)+c(p).Math.x(np)+c(p1).Math.x(np1)+ . . . + . . . +c(1).Math.x(n2.Math.p+1)+c(0).Math.x(n2.Math.p), wherein x( ) are the transposed samples and c(0), . . . c(p) are the real coefficients of the filter; and being adapted for, during a cycle for determining the value of the filtered sample y(n): calculating the first terms c(0).Math.x(n), c(1).Math.x(n1), c(2).Math.x(n2), . . . , c(p).Math.x(np) by multiplying the respective coefficients and transposed samples, and storing in memory said first calculated terms; reading the second terms c(p1).Math.x(np1), . . . , c(1).Math.x(n2.Math.p+1), c(0).Math.x(n2.Math.p), calculated and stored in memory during previous cycles for determining the value of filtered samples y(nm); and determining y(n) by summation of the first and second terms.