A form of digital filtering whereby audio data is oversampled and then decimated to the required 44.1kHz. In practice, the sampling rate is 64 or 128 times 44.1kHz. A digital brick-wall filter is then applied to the data, resulting in a perfectly phase linear transformation. [This type of filter is impossible in the analog domain due to the phase-shift caused by very steep roll-off filters.] See FIRIIR. After the data have been filtered below the Nyquist frequency, the next step is decimation where the data are re-sampled to produce an output stream of 44.1kHz, with the attractive result that the excess data thereby provides increased bit-resolution. See anti-aliasing filterreconstruction filterDSD.

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