Do amps really have different signatures? - Page 9  

Originally Posted by Anaxilus 

Much like the biased vocabulary used in the 'authoritative' oft linked garbage often linked as biblical reference here?  No, not nearly.

Originally Posted by stv014 

Assuming that the blind test is valid...

Originally Posted by stv014 

 

Assuming that the blind test is valid (it may or may not be), I wonder if the following:

 

"This momentary aberrant behavior seems to occur whenever there's a particularly loud high frequency signal during an instant of high-complexity, where the DAC has a lot of work to do to sort everything out.  It's as if the ODAC just gives up, momentarily, and renders those instantaneous high frequencies like two blocks of styrofoam being rubbed together - to produce a very short in duration, but very loud distortion of information that the LX and the PB2 have no difficulty rendering cleanly."

 

is related to inter-sample clipping, as tested here on two sound cards, one with a CS4398 DAC, and another with PCM1792A (ironically, it is the more expensive latter one that fails) ? With my test sample, which is a mix of a 11.025 kHz sine wave at an amplitude of 0.8284 and 45 degrees phase, and a 15.025 kHz sine wave at 0.4142 amplitude and 0 phase, the problem is plainly audible on a DAC that fails. However, it is a rather unrealistic "worst case" signal and a similar effect is much less likely to occur at an audible level in typical music. When I mentioned this issue to the designer of the ODAC, he argued that it would never be audible with real music; from this response, and the fact that clipping problems are not easy to avoid with the ES902x DAC chips (as evidenced by the NuForce uDAC2), I suspect that the ODAC would fail my test, too.

 

Then again, maybe there was some more trivial problem, like the USB power not meeting the specs, and the DAC clipping already below 0 dBFS. Or the input stage of the iBasso amplifier clipping the output of the ODAC, which was the loudest of the three DACs tested. In any case, the subjective description of the problem sounds like some sort of clipping issue to me.

Originally Posted by bigshot 

That's a mighty big assumption for a test where the subject promised with a crossed heart to keep his eyes tightly shut so he wouldn't see what equipment was on the table in front of him, and had to dramatically feel his way back and forth to the chair between samples. I guess a simple preamp switcher with all the equipment totally hidden away was too difficult.

Originally Posted by xnor 

Wait, what the? You add two sine waves with the amplitudes 0.8284 and 0.4142 which has a peak of 1.2426 and you wonder about clipping?

Originally Posted by stv014 

 

It has a peak amplitude of 1.2426 after reconstruction, but less than 0.99997 in the case of the digital signal, because the first tone with sample rate / 4 frequency is phase shifted by 45 degrees. This can be seen on the first picture, where all the dots (the digital samples) are within the 0 dBFS white lines, but the reconstructed waveform has peaks greater than 1.2.

I do not say that this effect was necessarily (or even likely) responsible for the audible differences, but I wanted to include all possible explanations. The other two (issues related to USB power or the input stage of the amplifier) are obviously more probable, especially since from the description it sounds like the clipping was relatively severe. Although I did see the clipping effect shown above mentioned somewhere as a potential source of positive ABX results when comparing audio with sample rate conversion.

Originally Posted by stv014 

Well, I gave the test the benefit of doubt, especially since this time actual artifacts that sound like clipping were described, rather than the usual set of vague "placebo" differences.

Originally Posted by bigshot 


I'd like to read a real scientific test that describes sound as "dark brown and liquid with a bit of transparency around the inner resolution"!
By the way, I think Xnor has a question for you.

Originally Posted by Happy Camper 

I've noticed here that the stanch objectivist trusts nothing and no one. The Pope himself wouldn't be taken at his word because everyone has an agenda.

Originally Posted by bigshot 

What kind of headphones does the Pope use?