Originally Posted by groovyd
in theory 48khz allows for a 24khz bandwidth of which they say humans only have about 20khz range of hearing. so the extra 4k would be for good measure but the reality is all of this makes a number of assumptions that are not true in a real system.
recognizing nyquist theory is one thing but if you think for a second about how that sampled waveform will look you see that 2 samples per cycle is really not enough even at a minimum. take a 1hz sine wave and sample it 2 times per cycle. it is entirely possible that both of your samples fall at EXACTLY the two zero crossings that occur in every cycle once on the way up and again on the way down and your reconstructed output becomes a flat line. by this it becomes pretty clear to see that 2 samples per cycle really is not enough at all to reconstruct your sine wave. nyquist theory assumes a number of ideal conditions, none of which hold in a real sampling system. it merely represents an absolute bottom line minimum spec requirement if you want to represent ANY of the information at a certain frequency but not necessarily all of it in all circumstances. infact given 2 samples per wave taken at any point in the cycle i can draw for you an infinite number of possible near sine waves of different amplitudes that pass through those points. lets assume the amplitude of the signal matters. by raising the sample rate beyond the nyquist rate you quickly begin to remove the singularities and the multitude of waveforms that fit the samples for a given frequency and you allow breathing room for the realities of the limitations of a real sampling system, such as non-ideal pre-ADC bandpass and post-DAC reconstruction filtering.
if we assume 20khz is a reasonable limitation of human hearing without regard for the fact that our amp, speakers, etc further attenuate the response at these edge of spec frequencies
then 48khz is really still an absolute minimum. in my opinion 96khz gives plenty of breathing room to counter all of the additive realities of a true system from end to end.
I tend to disagree, but let's say you're right, bad luck we get only one or even no usable sample, then your example would make some crap for 1 and only 1 period of a 22.05khz sine. a sine that will be cut out by the low pass filter anyway.
and for everything lower, your example becomes false as every other frequencies will get more than 2 points of reference with 44.1khz. that 1khz sine will get 44 samples, it's gonna be hard to misinterpret that one when 2 could be enough.
I am still in favor for 48khz to be sure that no one will mess up the low pass filter. but it's more as a security against pieces of gear done badly than a real need. doubling everything for "just in case" peace of mind at frequencies most of us don't hear, on audio systems that roll them off or cut them out, I fail to see the point.
Originally Posted by Digitalchkn
Originally Posted by bigshot
There is not plenty of energy beyond 20kHz with acoustic instruments.
I have spectrum analyzed lots of commercial "hi-rez" classical and jazz and saw that modern systems can pick up spectral content to no less than 30KHz. Even older recordings made during the infancy of magnetic medium have a positive SNR beyond 20KHz.
Basically if you take your redbook audio recording of your acoustic instrument and your 22.05KHz frequency point is wiggling in your spectrum analyzer then there bound to be energy beyond 22.05KHz. It's a different debate whether you or I are able to hear a test tone up there or not.
As an engineer, I ask myself how much deterministic energy is up there and if it's sufficiently large then I would want to capture it. Oddly enough, I have yet to see some analysis tool that plots integrated energy(power) over frequency as it applies to audio applications. That would allow one to determine 90 or 95% bandwidth requirements.
I understand the idea, but I'm completely against it for the exact reason you want it. I see that as an added chance to damage my hearing, and even though the sound pressure and duration are what count most, high freqs have more energy for the same amplitude right? I remember reading something about violin players and hearing loss where instruments making high frequencies were seen as more dangerous overall. and some hearing protection dealer saying that what was most important was to stop high freqs when they made some for me.
I really do not want my ears to receive too much of something I don't hear, but could still had damages on the long run.
well in my case it's not a real problem as pretty much none of my headphones/IEMs are able to deal with 20khz anyway, and most IEMs I've owned were almost dead silent above 14 or 15khz ^_^.