Quote:
Originally Posted by gregorio /img/forum/go_quote.gif
...there is no point in cans that can go up to 35kHz, humans can't hear that high and CDs contain absolutely no freqs above 22kHz.
|
As has already been said, the more extended (...into infra- and ultrasound) the frequency response, the more even the frequency response in the audible range. High- and low-pass filters such as the natural drop-offs shown by sound transducers don't have infinite steepness and ultra-sharp slopes, so every bandwidth restriction comes with a quite large adjacent area suffering from nonlinearity.
And let's not forget that every filter introduces transient distortion -- the steeper and the sharper the slope, the more so; and the closer to the usable audio band, the stronger the impact.
As to the CD cutting off ultra-high frequencies: That's exactly a case of a steep and sharp-edged low-pass filter as described above.
Quote:
Originally Posted by nick_charles /img/forum/go_quote.gif
All true, but even 20K is not really often necessary for music. If you apply low pass filters to music files you find that you can be really quite draconian without making an audible difference, few MP3 files have much above 16K yet can be near impossible to tell from uncompressed music. I did some experiments myself and with some music samples a 13K lowpass applied to wav files was undetectable (in blind tests)...[/i]
|
That's not exactly an adequate test: The sample used has already passed an extremely sharp low-pass filter. What you do is switching another (most likely smoother) low-pass filter in series. Now take into account that there are some CD Players with switchable filter characteristics, some of them largely corresponding to your filter -- with the goal of reducing the HF ringing (Gibbs phenomenon) introduced by the anti-aliasing filter -- and apparently some success in this regard.
I have tried a similar filter, the Meier «Analoguer» circuit, in my headphone system. The sound change it produced with CDs wasn't glaring, but an absolutely enjoyable smoother sonic variant with a tad less sparkle and harshness -- all in all neither better nor worse. With SACDs, OTOH, it blatantly annihilated their sonic advantage over redbook CD in the form of higher high-frequency resolution, detail and airiness. For me this test result is a clear hint that a sharp high-pass filter at ~21 kHz is bad for preserving detail and transient accuracy within the audio band.
Quote:
Analog FM stereo for instance has nothing above 15K. |
Not true! I have always wondered why FM stereo didn't exhibit the often cited (and to my ears existing) «digititis» of the CD format, particularly the first CD player generations. And I realized what the fundamental difference was: Apparently the radio sound is much less clean, it has lots of distortion, even at the best reception conditions. And distortion is exactly what prevents the FM radio's bandwidth limitation from sounding sterile -- in contrast to the CD format. In the latter case
all overtones are highly affected by the filter ringing -- they lack accuracy and sharpness, are heavily smeared around the time axis --, whereas with FM radio «time smearing» is less of an issue, firstly because the filter is less sharp, secondly because beside smeared overtones there's still a considerable amount of unsmeared overtones in the form of harmonic-distortion products (up to 20 kHz and beyond!) -- making for a more organic sound. The same applies to some tube output stages with some CD players and DACs.
.