jarome wrote: > The Nyquist theorem says that sampling at twice the highest frequency in > the source will reproduce it perfectly. So 44.1 kHz will get to 22 kHz > in principle. But it is critical that there be NO signal above half the > sample rate, or it is aliased below the 22 kHz into the audio band as > bad distortion. >
In fact DACs for high fidelity use have been built without anti-aliasing filters. Some of them are sold commercialy and are highly admired by some audiophiles. In general they don't sound all that bad because program material with significant content above 20 KHz is relatively rare. Secondly many modern DACs have what are called Linear Phase filters and they work as advertised. Their phase shift characteristic closely matches that of a regular short delay, so in a certain sense they have no excess delay beyond that which is inherent in playing a recording some time after it was made. > > So, players must have a sharp low-pass filter in the stream. > False for the reasons given. > > The problem with this is that if the amplitude response has a sharp > cutoff, the phase response oscillates wildly. > This is false even when linear phase filters are not used. The phrase "oscillates wildly" while poetic, is not accurate. The oscillation is damped. and therefore brief. Furthermore it can be completely eliminated if the filter has what is known as a minimum phase characteristic which is possible to achieve fairly economically given the continually falling cost of digital logic ceircuitry. The damped rinigning takes place at the Nyquist frequency which in a common CD player is outside the normal audible range. > > The number of bits, to my ear does make a difference, especially on loud > congested music, for example a symphony playing many parts loudly and at > the same time (ives Symphony No. 3). 16 bits gets congested. It is hard > to have the instruments maintain their unique place in the soundstage. > In principle, by doing some slights of hand (interpolating -randomly- > between bit levels) CDs claim to be able to get 19 bits, which might be > sufficient. And I have heard some very good sounding CDs. But not that > many. Remember that with 16 bits, there are only 65,000 levels (half > negative), so there is a inherent 1/325 % distortion due to imperfect > representation of the sample height. > I care more about 24 bits than 96 kHz, since I am old and am lucky to > hear above 15 kHz. The above comments that I am trying to correct here are false for the reasons given. I can debunk the second paragraph as well, but I think the proven falsehoods in the first paragraph that I corrected make my point - which is that these kinds of comments are false and constitute a kind of religious faith that is not uncommon among poorly-informed audiophiles. Knowlegable audiophiles simply know better. ------------------------------------------------------------------------ arnyk's Profile: http://forums.slimdevices.com/member.php?userid=64365 View this thread: http://forums.slimdevices.com/showthread.php?t=106935 _______________________________________________ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/mailman/listinfo/audiophiles
