One embodiment of the present invention discloses a data access method comprising: (a) receiving a plurality of data units consisting of filtered data units and un-filtered data units; (b) filtering the filtered data units; (c) storing the un-filtered data units; (d) recovering the timings of the un-filtered data units stored in the step (c) according to the received timings of the data units received in the step (a); (e) inserting replacement data units to replace the filtered data units, wherein each of the replacement data units has the same timing as each of the filtered data units; and (f) outputting the un-filtered data units and the replacement data units according to the timings of the un-filtered data units and the timing of the replacement data unit.