|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
71.112.27.9
In Reply to: They're One and the Same!!!! posted by Todd Krieger on February 24, 2007 at 19:10:58:
HowdyYou need to read and understand a basic digital signal processing book or take a class in the subject.
The interpolation you talk about is the digital filter I'm talking about.
The process of zero stuffing followed by (digital) filtering at 1/2 the input clock freq is exactly the correct way to raise sample rates by an integer.
The process of filtering at 1/2 the output clock rate and throwing out all but every Nth sample is exactly the correct way to lower sample rates by an integer N.
The process of zero stuffing followed by (digital) filtering at 1/2 the lowest of the input and output clock freqs and then throwing out all but every Nth sample is exactly the correct way to synchronously sample rate convert by an integer ratio.
If this isn't clear I'm sorry but I'm dumbfounded in that I don't know where to start to make it any clearer.
Follow Ups:
The problem is, Ted, is people mention the zero-stuffing part, and not the interpolation part. And then equate oversampling to zero-stuffing with no further process.Personally, what should be omitted is the "zero-stuffing". In the whole process, this part is trivial. (I personally would have called it "new placeholders" for the interpolated data.) The "interpolation" is the important part of oversampling. And it shouldn't be treated as separate from oversampling. Because it cannot even be executed without oversampling.
In fact, Ted, it's been used by some CD player and DAC manufacturers to dupe customers into thinking oversampling is "zero-stuffing" and interpolation is an "innovation" by the manufacturer!! Most people don't even realize it's deceptive advertising.
And I'm sure there have been quite a few products brought to market based on misconceptions about oversampling. I think the number of products that mangle the signal to be alarmingly high.
And then audiophiles complain about the sound, and engineers complain about audiophools criticizing what they think are products of superior fidelity.
And in practice, I'm not sure if the zero-stuffing part even takes place!! The oversample values may just as well be overwritten once the new data replaces the old. Had the concept been stated that way, there wouldn't have been so much confusion.
HowdyManufacturers aren't as technically illiterate as you make them out to be. Some (dCS for example) chose to use interpolation strategies that aren't based on filtering (and hence aren't mathematically optimal) they may be better by some other criteria (perhaps the designer's ear) and they are certainly less math. Most designers put their mark in by making different choices of how to implement the filter, e.g. FIR vs. IIR, minimum ripple or minimum phase...
Of course zero stuffing takes place in SSRC, you simply avoid multiplying by the samples you know are zero.
Like I said before, you should really implement these things for your self so you get a feel for them. If you can't implement a FIR filter with the desired impulse response or filter shape then you shouldn't be speculating about how these kind of things work.
I think misconceptions of classic oversampling played a major role in asynchronous conversion getting off the ground.ASRC, in my humble opinion, is a process that should have never found its way into consumer digital audio playback products. It was originally intended to convert data for transfer from one media format to another, not necessarily in real time.
But technically-corrupt products do make it to market when sound concepts are mis-characterized. And very few concepts have been a bigger victim of this than classic oversampling/digital filtering. The "old fashioned" 8x oversampling IMO is still the best method of digital filtering that we have. Where the innovation lies is in the FIR filter function, which is still the one part of CD playback design that I think has room for vast improvement.
HowdyYou continue to speculate about cause and effect of things you have no personal knowledge about.
.
HowdyYou should have heard jj in person about some of the people here :)
.
I found it hilarious last year when he got so incensed he started accusing me of things that Todd had said :-)I will admit I baited him a little, but I didn't expect him to swallow the bait, hook, line and sinker and then choke on it :-(
This post is made possible by the generous support of people like you and our sponsors: