TerryS;676011 Wrote: > For the most part, I think we agree on what dithering does, but here is > where I fundamentally disagree. Read carefully what was said in the > link you posted ... > " > This result arises because the added noise breaks up the tendency for > every sinewave cycle to be distorted into exactly the same (incorrect) > shape as all its neighbours. A regular and repetitive distortion is > replaced by a noise background. > " > Dithering doesn't prevent or fix the distortion of an individual > sample. It just causes the distortion to vary randomly so that it is > less noticeable. The distortion is randomized. To me that is a huge > difference. > > Let's get back to basics for a moment and forget all of this dithering > and FFT stuff. > Sound is the compression and rareification of air molecules. The > instruments cause vibrations that compress the air. This is amplitude > modulation. The loudness of the instruments is amplitude modulated on > the air. It is not frequency modulated at all. The frequency just > comes about as the rate at which the amplitude varies. > It is the job of our recording and playback system to capture the > amplitude variations of the compression waves, store them, and later > play them back as exactly as is possible. There are many ways to do > this. We could let the compression waves impinge on a diaphragm that > vibrates with an amplitude that is proportional to the wave amplitude, > and let that diaphragm modulate a needle that cuts a vibrating groove > into a wax cylinder. Later we could reverse the process and let the > wiggles in the wax amplitude modulate a diaphragm that amplitude > modulates the air to form identical compression waves to those we > started with. If the compression waves we recreate are identical to > the ones we recorded, then we have a Hi-Fidelity audio system. > I don't mean to imply that you have to stay with amplitude modulation > all the way through the system. You could convert the amplitude > modulation to frequency modulation or digital samples, or whatever you > like, so long as what you end up with is amplitude modulation that is > identical to the modulation the instruments impinged on the air. The > important thing is to preserve the exact amplitude vs time relationship > that we started with. > Dithering does not preserve this amplitude modulation. It does cause > the distortion due to limited sampling resolution to be much less > noticeable, so it does have a benefit and is an important technique. > But making the distortion less noticeable is not the same as preventing > the distortion (IMHO). But at this point we leave the world of what we > know and enter the world of what we believe. As you have correctly > pointed out, dithering converts the distortion components into noise, > and all systems have noise. So now we have entered the realm of > opinions. Some people say that 24 bits is required to faithfully > reproduce the music and keep distortion and noise below objectionable > levels. Some say 16 bits is enough. Some say a compressed MP3 file > sounds fine to them and there is no need for higher fidelity. > But my point is simply that dithering is a technique that changes the > distortion to make it less audible or objectionable. It does not > prevent the distortion. The amplitude sample is still wrong by the > same amount. I just like to point this out when people claim that > dithering prevents distortion. > Terry Once again you have said nothing other than that you refuse to accept the distinction between noise and distortion. You have no other point. The point has been made over and over again that dither turns distortion into noise. It actually increases the (total distortion + noise).
The only question remaining is therefore what is the acceptable noise level bearing in mind that oversampling and noise shaping can reduce the noise level in the audible spectrum further. -- adamdea ------------------------------------------------------------------------ adamdea's Profile: http://forums.slimdevices.com/member.php?userid=37603 View this thread: http://forums.slimdevices.com/showthread.php?t=89733 _______________________________________________ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/mailman/listinfo/audiophiles
