Originally Posted by
Currawong 
From my experimentation with various pieces of gear, the "bright" comments may be the result of noise or distortion of some sort in the treble. Plugging various pieces of gear into a power filter with a measured attenuation of noise removed this.
While one would assume that manufacturers would test their kit under optimal conditions I think electrical noise may frequently be over-rated as a problem, I inhabit a 1948 built house with the original ungrounded wiring, it is a disaster zone electrically and our light-bulbs blow with alarming frequency, sometimes when the air con switches off it is impossible to get the kitchen light to switch on, ( we really should get the house rewired) many of our power strips are bodged with cheater plugs, despite all of this we do not have a notable noise problem on any of our many audio systems. Perhaps we are lucky.
I would also ask for better evidence of the effect of power filters on fundamental audio parameters, measured noise reduction is one thing but I would want to see measured differences in FR and so on, plus of course some DBTs showing that the electrical noise reduction was audible in music as opposed to listening to digital silence where it would be easy to notice...
When I owned an Audiovalve RKV, I plugged it into my noise-filtering board and my subjective impression was of a more "black background", as if some haze over the music had been removed. This is the kind of thing I would like to measure and understand. Compared to my Phoenix, the power supply in the RKV is considerably simpler in design. The Phoenix isn't affected by the noise filtering (presumably the PSU does that). If anything, it sounds worse filtered, so into a regular, unfiltered socket it gets plugged. My friend sold his Benchmark, so I regret I cannot experiment with that too.
It would be interesting to see how the measurements of each amp or DAC I tried this with are affected.
Agreed !
Related to that, an interesting comment from a DAC maker I read was that he said he could tell how a DAC would sound by its ability to reproduce a square wave.
Above 5k (I think) a square wave and a sine wave of the same frequency are perceptually indistinguishable, it is impossible for a DAC to render a perfect square wave due to the whole infinite harmonics thing, square waves do not occur in nature and seldom in music, they are useful things like testing rise time i.e getting an idea of transient response, but it is a bit of a parlor trick, it is the sort of trick vinylies use to prove that LP is better than CD after all 
I was thinking specifically of the Beta 22 measurements on amb.org which show it doing a great job of reproducing a square wave. There are also measurements of the amp when it is powering varying impedances. I think we need more people here who actually build audio gear to talk more about their designs and how they relate to measurements and performance. Excepting those manufacturers who don't provide any (such as NOS DAC makers) I do see some willingness. However, Dan Lavry did try, but copped a load of unhelpful abuse for it. Many of the measurements we see are only of equipment reproducing a sine wave at 1kHz, which doesn't really explain how they perform when playing back music. AMB seems to have come closest to providing measurements that do give us some idea.
A lot of gear can't reliably do this (depending very much, I imagine, on the input impedance of what it was connected to)
so that may be another factor that doesn't show up in regular RMAA tests. I think a lot of you are looking at manufacturer's specs or RMAA tests and assuming you've seen all there is to see.
