You can refer to this for a relation between SFDR and INL: http://www-inst.eecs.berkeley.edu/~ee247/fa07/files07/lectures/L14_f07.pdf
On Wed, May 9, 2012 at 11:25 PM, Hal Murray <[email protected]> wrote: > was Subject: Re: [time-nuts] Faster than light of a different type > (Probably my fault.) > > [email protected] said: > > What I found funny was that the Audiophlie and light thread drew such > > attacks when it hit home to me as exactly what the Time-Nuts mission is > > about. The Audio thread touched on some real world time and freq > research > > ... > > I too enjoyed the technical discussions. Thanks for your contributions. > > It's the audiophool bashing that people are complaining about. Sure, it's > fun, but only at the right time and it gets old quickly. The problem is > that > with large groups, there are different opinions of when and how much is > appropriate. The long tail on opinions of reasonable can annoy a lot of > people. > > ----------- > > Back to technical stuff... > > As a practical matter, is clock jitter or phase noise from a typical low > cost > crystal and decent board layout a significant problem in audio gear? How > hard is it to measure? > > Is clock accuracy a practical problem? How good are people with perfect > pitch? It wouldn't surprise me if there are a few that are much much > better > than others, but how good is that relative to 50 PPM which I can get in a > low > cost crystal? > > Video geeks solved their clock distribution problems by using frame > buffers. > Is there a similar trick for audio? Is there a need for it? > > -------- > > I know clocking is a serious problem in fancy DSP systems. For example, > modern radar has gone digital. In that context, clock jitter can be > important. Standard procedure is don't run your clock through a FPGA > because > it will add jitter. > > Part of the problem is that they are doing magic down conversion in the > ADC. > (I can't think of the term.) Suppose you have a 100 MHz signal with a 1 > MHz > bandwidth. You don't have to sample at 200 MHz. You can sample at 2 MHz > and > your signal will alias down. It's turning what is normally a bug into a > feature. The catch is that the errors/noise due to clock jitter happens at > the high frequency, in this case multiplying the noise by 100. (Your > sample/hold at the front end has to work at the high frequency and your > anti-aliasing filter gets more interesting.) > > There has been an interesting change in the specs for ADCs and DACs over > the > past 20(?) years. They used to be specified using terms like DNL and INL > and > No-missing-codes. Modern high-speed ADCs are specified with terms like > ENOB > and SFDR. Data sheets often include several plots of a batch of samples > run > through a DFT so you can see the noise floor and such. > > Here is a reasonable glossary: > http://pdfserv.maxim-ic.com/en/an/AN641.pdf > > I don't remember comments/specs about clock jitter in the data sheets but I > haven't looked at one in a few years. I'll have to keep an eye out the > next > time I'm browsing. > > > > -- > These are my opinions. I hate spam. > > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
