I'm no tech, but here's how I see it:
1990s-2003
1)Capacitor/inductor/coil based (Shunyata, Audience). Simple components placed over the lines, in the hope of breaking-up noise. I don't think these worked too well. The Teflon-equipped Audience (2008) was an improvement, but at a high cost...
Not for analog sources or tubes:
In audio history, thumbs-down for cable lifters, green paint for CDs, clock radios (to reduce RF), 'speaker bullets', DSP bass-correction (peak flattening), bass traps and 'soundstage-expansion' devices -like Stein Music. This Stein, with multiple units, made...
These type were rare in 2010, now they're surging.
Current production, player or processor, made in U.S. or U.S. presence.
Multiple price points if apply:
Up to 3k: Border Patrol, Monarchy, Denafrips, Audio-gd, MHDT, Holo, Soeskris, Metrum, Schiit
5-15K: Audio Note, MSB, Metrum, Computer...
They shout, they 'honk', they have pronounced coloration. Not true anymore -they're the fastest growing audiophile speaker today. If we include the waveguide-style horn. A growing list of reviewers have them in their systems.
Waveguides: Devore Organgutan, GedLee, Amphion, Tannoy, ATC, Emerald...
Ones that went WAY beyond anything, at the time. Includes the year of release.
1992 -Madrigal-Levinson No.30 DAC $15,000
1994 -Wilson X-1 speaker $65,000
1997 -Boulder power amp $59,000
1999 -Rockport turntable $73,000
2003 -Boulder phono stage $29,000
2005 -Tara 'Zero' interconnect $15,000
...include, from U.S.-Canada -EMM 2X, Berkeley Alpha Reference, PS Audio "DS" and Bricasti M1.
From Europe -Gryphon Kalliope, Total DAC and CH Precision C1.
They're either stripping the DAC-chip down or using discrete resistors. Much better than ever before - digital (finally) came of age...
I am not an engineer - but I still have a right to raise these issues (concerning "testers" like Stereophile, etc.)
-Don't show SID distortion figures or high-order non-linear distortion at lower levels.
-Quote at a single frequency.
-(Makers) rate distortion in volts - not power. Don't...