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Originally Posted by Fred  Actually Bob that is only true for my older vacuum tube opamps which have distortion in the 0.006% range. My JFET-993 opamps (which I've been using for about 5 years now) have 75- 80 dB open loop gain and THD+N figures in the 0.0002% range. |
Dear Fred: It's good to see you on this forum! 0.006% is fantastic for a vacuum tube anything! If "fantastic" is the right way to rate a unit just on the numbers...
Anyway, the point I was trying to make to Philip still stands, that nothing is "perfect" and that his idea that my "system integration" approach is wrong, and "to compensate for imperfect loudspeakers" is simply a complete misunderstanding of the art and the science of putting together a mastering-quality reproduction system.
One of the criteria for a high quality reproduction system is the ability to hear distortion in the sources and recognize it, and to hear and not miss inner details in the sources. There's nothing written in the technical books about that per se, the idea is that the monitor section should have low measured distortion on its own so as not to mask distortion in the source, and that is a precept. However, investigations by some designers that I know are showing that a certain amount of low level measured distortion may be desirable as it reveals depth in the sources.
When does distortion cease to be a negative and become a positive (in either direction)? That debate will go on long after I'm dead.
Distortion can be harmonic, temporal (acoustic, e.g. diffraction), inharmonic, mask in different frequency areas. It's a very complex concept and nothing, not even the most "objective" measurements, comes close to describing the holistic approach and integrated approach required to assembling a world-class monitor system.
And it's a continual struggle. The addition of some bass traps to my room improved the linearity (and definition) in the bass and other regions, but audibly removed some high frequency liveliness, dynamics and clarity. Shroeder curve measurements then confirmed that the reverberation in the upper midrange and highs had been reduced below the Shroeder recommendations that reverb time should be even in each octave band above about 125 Hz. Some diffusors were constructed and installed. Listening then confirmed the improvement from the diffusors and a further Shroeder test agreed with the positive listening. Objective and subjective, art and science live side by side, day in and day out.
Another example: Changing the power amplifier from a well-known Class A amplifier to a pair of Lipinski Class D Mono blocks improved the low frequency definition and extension in the room. The high end and upper midrange were equivalent. All of this judged by listening. But playing my shuttle launch recording, the subwoofers now bottom out (overload) at two moments in the playback where they did not before. The theory is that the Lipinskis frequency response may extend down further at the bottom end into the subsonic than the previous amplifier. This "improvement" introduced a problem that had been taken care of before by the slightly less extended bottom end response of the previous amp. Who is to say which is more or less "perfect"?
BK