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Re: You might be interested in this ...

Posted by Werner (A) on March 2, 2007 at 00:07:15

In Reply to: Re: You might be interested in this ... posted by Christine Tham on March 1, 2007 at 13:26:53:

"but I wouldn't rate ... as "near perfect". Perhaps I'm more picky than you."

The context of our subthread is the list of comparative tests at the src.infinitewave.ca site. 'near perfect' in that context means the absence of the blatant non-linear and aliasing artefacts that many of the tools display.

"Even Audition doesn't generate "near perfect" results - ... the resultant file was quite different from the original (more than 1dB amplitude differences for frequencies higher than fs/4)"

That's contrary to my experience then. I can't see any gross artefacts from Audition's SRC. As for uncontrolled listening ... yes, of course we feel that something is wrong after SRC ;-)

"even using Audition "999" pre and post filter."

I never use the pre/post filter. A cursory inspection of the SRC's impulse response shows that enabling the additional filter does strange things to the response tails. You'll also see this in the raised wideband noise floor in the measurements at the src. site.

Leaving the filter off and living with a bit of aliasing (I'm only interested in SR reduction) is IMHO a better option. Mind, the ear is pitch-insensitive above ~12kHz, so aliasing in the band 15-22kHz only increases the perceived brightness, and is not perceived as non-harmonic distortion. dCS use this strategy, among others. Also see iZotope in its Mid position.

"Even if you could embed a real time "near perfect" software implementation of SRC into a DAC"

Why would you want to do that? If one wants to increase SR from, say 44.1k, to something higher, in real time, then by all means go for integer oversampling. A 1001-tap 40-64 bit FIR with massively better specs than what you see in typical consumer/pro DACs and filters is perfectly feasible in a modern FPGA. And for the DAC itself it really doesn't matter if it is clocked off a multiple of 88.2kHz or 96kHz.

"*** Have a look at the Weiss and the Z-Systems. ****
I wouldn't consider either of these to be "near perfect" either"

Neither do I. But you asked for examples of hardware implementations.

"As I've said before, not necessarily bad design or coding. Tradeoffs between speed and accuracy are a far more likely reason"

Oh yes. Many of the results on that website originate in either ignorance or contempt for the object at hand (music!). This is (mostly) all software intended for batch processing. Speed as such is not very relevant. What's the point of a 10x reduced processing time when the result of it will be - forever - at a /10 quality?

Many of the implementations showcased here are outright unacceptable for a signal processing point of view, and I really cannot think of a valid excuse for that.

bring back dynamic range

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