Hi! About a year ago I noted that the linear filter (signal.lfilter) had a bug when filtering 3D matrices: http://www.scipy.net/pipermail/scipy-user/2002-March/000201.html Working in Unix I made a fix in the sigtoolsmodule.c RawFilter code: while (num_loops--) { filt(ptrb, ptra, ptrX, ptrY, ptrVf, filt_size, len, stride_X, stride_Y); incr = increment(loop_index, ndims, max_index); /* Returns number of N-D indices incremented. */ k = ndims - incr; if (num_loops > 0) { /* Adjust index array and move pointers to right place for next iteration */ if ( k==0 && ndims==2 ) { ptrX -= loop_strides_X[1]*(max_index[1]-1); /* Stride information */ ptrY -= loop_strides_Y[1]*(max_index[1]-1); /* 20020304 */ } ptrX += loop_strides_X[k]; /* Stride information */ ptrY += loop_strides_Y[k]; which I think fixes the problem for the 3D case I now increasingly work in windows, so I wonder if you would consider fixing the problem I haven't been able to compile the fix and make it work in windows yet. Claes Hagström -- Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/