[Elecraft] SO2R thoughts

[Jim Brown]

On 3/30/2014 10:38 PM, Stephen Bloom wrote:
> especially something like "fatigue" is pretty subjective

As a retired pro audio engineer and member of both the AES and the 
Acoustical Society, I've had to understand issues like this. The study 
of human perception and reaction to sound is called psychoacoustics, and 
the Acoustical Society has many members studying this stuff at very high 
levels.

It is VERY well known that listening fatigue related to the listening 
system correlates with two factors -- distortion and loudness.  Poor 
spectral balance is a form of distortion, but the most obnoxious 
distortions are non-linear distortion -- what we try to describe as 
harmonic distortion and intermodulation distortion -- and distortions 
associated with A/D and D/A conversions.

As Al Lorona has noted, the distortion produced in ANY system is 
strongly related to signal levels, and how gains are set. Do it wrong 
and you can make things sound nasty in a hurry; do it well and 
everything is mellow. if you think your radio is fatiguing, you probably 
don't know about all that great stuff that Al posted.  As to the digital 
distortions -- much of what we hear occurs if we are listening too close 
to the the top or bottom of the converters. Again, getting the gains set 
right avoids that.

I measured my first K3 (in the first year of production) and found 
excessive distortion in the Line Outputs that resulted from wrong-headed 
design of the output stage (it was done by a digital guy, who added 
resistors between the output stage and the transformer because he 
incorrectly thought audio stages were"600 ohms" -- they have not been 
for at least 50 years).  I communicated that to Wayne, and it was 
quickly corrected.

73, Jim K9YC