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In Reply to: Foobar and SRC. posted by twystd on September 7, 2006 at 18:44:10:
This is a complex subject, I did a lot of experimentation on it last year, here is what I found:Upsampling to a DAC with a digital filter (ie an oversampling DAC) usually makes them sound better. The primary reason is that the brickwall filter frequency is directly related to the sample frequency, if the sample frequency goes up, so does the filter frequency. Getting the filter higher up above the audio band almost always helps.
You can change this sound significantly by adjusting the upsampling frequency and how its done. An integer upsampling almost always sounds better, so use 88.2 rather than 96 for CD files. (this is all assuming the upsampling is NOT being done by an ASRC chip, those have their own problems). Even at 88.2 you can get changes in sound by choosing different upsampling algorithms. I'm not going to tell you which is the best, its a very personal thing. I've done the tests where two people in the same room, same system etc. prefered different algorithms.
I've yet to run across a situation where going to higher than 88.2 for CD improves the sound. The only reason I would ever use 192 is if I had a true 96 original, and even then I'm doubtful about the outcome. Yes the modern chips are all supposed to run at 192, but every measurement I've made with chips running at 192 has been worse than with 88.2/96. The jitter goes up, distortion goes up etc. As far as I can tell this is because there are a number of timing parameters in the chips that are fixed, as the sample rate goes up these wind up being larger percentages of the sample time.
For a DAC without a digital filter (ie a NOS DAC) it gets much more subtle. Using software upsampling CAN improve the sound but its going to be very DAC and system dependant. It can also degrade the sound!
The common NOS DAC has no filtering either digital or analog after the DAC chip, relying on the downstream components or the human ear to do the filtering. This may or may not be an issue. Upsampling will move the ultrasonic frequencies up higher which MIGHT make an audible improvement. If the DAC chip being used only has 16 bit resolution (such as the infamous 1543 DACs) The upsampling cannot "smooth out" the waveform so it might actually make the sound worse. If your NOS DAC uses a bit more modern chip that can handle greater than 16 bits and is designed for higher frequencies upsampling could actually improve the sound.
Again I would not use 96 for CD sound but stick to 88.2.
With NOS DACs I've been finding out that one of the things that makes them sound the way they do is that a lot of DAC chips sound better when run at slow speeds. Its those fixed timing parameters again. If you don't have any oversampling then those fixed parameters are a very tiny fraction of the sample period, much less than with the traditional 8X oversampling.
So a 2X upsampling (88.2) can push the ultrasonics up a lot, which can significantly improve the sound for some systems/people, and is not decreasing the sample period THAT much so the fixed timing parameters are not degrading the sound significantly.
Its all a balancing act!
John S.
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- Re: Foobar and SRC. - John Swenson 13:00:03 09/11/06 (0)
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