| 摘要 |
A digital FIR filter 60 comprises parallel portions 64 and 66 respectively operating at a high rate and a low rate. The filter consumes less power and has a lower delay than a conventional FIR filter, and may be used as one or more of the filters (32,34A,34B, 44, figure 3) in an ambient noise cancellation system (figures 1 and 2), many of these filters being adaptive filters. A delay element 74 may be inserted to match the total delay in the low rate path comprising the decimator 68, low rate portion 66, delay 74, and interpolator 70 to the total delay through the set of delays 62A in the high-rate path. In an alternative arrangement the digital filter portion 64 may be replaced by similar analogue filter portion (64a, figure 5). |
