adamdea;675595 Wrote: > > a.you simply refuse to accept the distinction between noise and > distortion > > [Digital sampling rests on the principle (discovered by Fourier?) that > any squiggly line can be made by taken a load of sine waves and > superimposing them. if your signal is suitably band limited (ie only > sine waves up to a certain frequency are allowed), then you can deduce > the formula fior the squiggly line by deriving from the sample data > the frequency phase and amplitude of all the sine waves. The squiggly > line must therefore have a "trend" in the sense that it follows a > mathematical progression] > > Now the sample values have limited accuracy, but if the error is > radnom (noise) you can still deduce the underlying squiggly line more > accurately than you can if the error is systematic (distortion) > > f. there is a connection between how fast the signal changes ansd the > number of samples per second. the number of samples tells you the > highest frequency you are allowed (nyquist anyone) ; and the highest > frequency determines the steepest slope you can have on the time domain > representation of the signal, ie how quick it can change. > g. musical signals are not random. When you make a musical note then > the same basci tones are played (albeit with decay)for some time. In > effect you have a tone and its harmonics superimposed which continue > for quite a long time RELATIVE TO THE SAMPLE RATE. Although new events > do occur (eg a new cymbal strike as opposed to the decay of one strike > over time) they don't occur all that often from the perspective of > 44kHz. > > I promised myself i wasn't going to waste lots of time trying to > explain something I only just about grasp > > But I have.
Gee, Sorry I caused you to waste your time yet again. I'm not being stubborn (all stubborn people say that). I'm truly looking for information. I am an Electrical Engineer. I have been designing ADC and DAC circuits for years. I know about dithering. I use a spectrum analyzer almost daily. I also use oscilloscopes in FFT mode to view the spectrum of signals. I often have to pull signals out of the noise floor to measure them. I even manually calculated FFTs on time domain signals in school (just to prove it can be done I guess). So please don't assume that I am j ust some malcontenet that has decided that CD quality isn't good enough (although this is true ;-). My point is simply that the lierature that I can find does not ever explain the benefits of dithering on anything but sine waves. Music is not random, but it is pretty damned close. Think for a minute about what the time domain signal is representing at any given instant. There will be some low frequency fundamental, that may indeed almost look sinusoidal. But on top of that, are any number of higher frequency signals. Some related to the fundamental, some from other instruments that are totally unrelated. Hell, there may be a hundred instruments, all with their fundamentals along with all their harmonics. Literally thousands of signals all added together with changing phase and changing amplitude. And all of them get added together to create that time domain signal. It is very random. Now I know that it doesn't change infinitely fast. Like you(and Shannon) point out, it can't change any faster than 22kHz in a 44kHz sampled waveform. But that's only two points for each sample. The next sample isn't likely to be at the same level as the previous sample. I would be willing to bet that almost never happens. So I disagree with your assertion that the tone and its harmonics stay the same for a long time relative to the sample rate. Look at a music waveform on an oscope. It just doesn't stay the same at all. Not even for a very few samples. And you will never find two consectutive periods of a wave that look anything alike. Dithering on a sine wave, does de-correlate the quantization error (distortion) from the sinal, and through noise shaping moves it out of the audible range. It doesn't prevent the distortion. It just moves the harmonic components out of band. Is this the same as having a distortion free signal, or just a trick to make the distortion sound less objectionable? We all 'know' that dithering can effectively increase the resolution of a ADC or DAC. But how much? Have you ever come across a number for this? Why not? Because it depends.... It depends on how many samples you can make of the signal before it changes. The more samples I can make on the waveform, the better it works. One sample does nothing. Thousands of samples will pull a signal out of the noise floor like magic. But I don't see how I can expect many samples on a music waveform. If dithering worked so well, why do I even need 16 bits? Wouldn't 8 bits work with enough dithering? Why not just one bit? Well like you pointed out, I could just use one bit. I just have to make the sampling rate really, really high. Show me the analysis that shows how much improvement dithering gets me on a typical music waveform sampled at 44kHz. I've been looking for 20 years.... Terry -- TerryS ------------------------------------------------------------------------ TerryS's Profile: http://forums.slimdevices.com/member.php?userid=40835 View this thread: http://forums.slimdevices.com/showthread.php?t=89733 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/audiophiles
