In Reply to: Why would I want selectable Digital Filters in a DAC? posted by jedrider on August 31, 2015 at 15:05:57:
The sample rate of 44.1 kHz for CD playback is the main reason why we've had digital filtering, because there is such a small gap between the generally-accepted top of the audible range (20 kHz) and half the CD's sample rate (22.05 kHz), the highest reproducible frequency per Nyquist's Sampling Theorem. CD is ideally reproduced with full passband at 20 kHz with full stopband at 22.05 kHz. Since ringing would be introduced with "perfect" filtering with the passband and stopband so close together, time "smearing" exists at the top of the audible band.
So the sample rate of 44.1 kHz for CD playback leads to a compromise, top-end frequency response versus time response. The DAC's filtering can be optimized for either flat frequency response or time response. Or somewhere in between.
Long filters generally do best with flat measured frequency response to 20 kHz, but have "smeared" (ringing) time response. (These filters closest resemble the ideal filter per Shannon/Nyquist.) Short filters have a slightly rolled off top end at 20 kHz, and better time (transient) response than long filters. Non-oversampling filter-less designs (NOS) do best with transients and time response, but have the most "rolled off" top, due to nulls/modulation in the sampling toward the top of the audible band.
There is also a choice between "linear phase" and "minimum phase" filters. Linear phase has zero average phase error through the frequency range, but minimum phase filters better resolve the attacks and decays in music. (NOS designs do not have this option.)
If the music is heavy in HF information or transients, a short minimum phase filter might be ideal. If the music is more continuous, like Samuel Barber's "Adagio for Strings", a long linear phase filter might be ideal. If the music is small scale like a folk ballad or string quartet, a NOS design might be ideal. Your mileage may vary.
No single filter is ideal for all music. I generally prefer short minimum phase filters personally, if I were to choose just one filter type. But other listeners might prefer other filter types.
And finally, if you're loaned a DAC with these filter options, you can find out which filter types are most suited for your music and listening. You can then acquire a DAC with the filter type you most prefer.
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Follow Ups
- Because...... - Todd Krieger 22:38:25 08/31/15 (12)
- So, PERFECT sound is not even possible! - jedrider 09:15:41 09/01/15 (11)
- RE: So, PERFECT sound is not even possible! - Todd Krieger 11:34:30 09/02/15 (0)
- But whatever sound it is.... - Ivan303 14:35:17 09/01/15 (1)
- Not possible, forever? (nt) - Crazy Dave 07:53:31 09/02/15 (0)
- What is perfect sound? - sbrians 12:33:19 09/01/15 (1)
- Doesn't matter, as long as it's "Forever" - genungo 13:04:35 09/01/15 (0)
- However, CD can be much better than most vinylphiles think - John Marks 09:54:30 09/01/15 (1)
- Agreed...... But......... - Todd Krieger 11:25:24 09/02/15 (0)
- Not at 44.1 kHz. nt - Tony Lauck 09:25:05 09/01/15 (3)
- RE: Not at 44.1 kHz. nt +10 - fmak 05:07:25 09/03/15 (0)
- Disagree. - jusbe 18:27:08 09/01/15 (0)
- RE: Not at 44.1 kHz. nt - ahendler 17:09:52 09/01/15 (0)