From a design perspective, distortion
in audio gear is a negative. The impulse is to minimize it and
yet, as an artistic tool, many "sonic color options" are needed.
It wasn't until the introduction of each new technology that the differences
between any two became obvious. In the sixties, it was the transistor.
By the mid-seventies, multitrack tape and consoles were purged of their
transformers in an attempt to recover impact (punch). In the late-seventies,
the SSL console was introduced. While essentially a "neutral" audio
device in that it is transformerless and opamp based, the SSL was initially
perceived to be starck and not particulalry complimentary, albeit an essential
production tool due to is Total Recall feature.
When first purchased by The
Power Station (NYC) circa 1977, Chief Engineer Tony Bongiovi normalled
Pultec Equalizers to the SSL's insert points in order "warm up" the signal.
This parallels the reaction to early digital audio, a mad dash to embrace
the vintage classics and determine the difference between what had been
and what now is. In a word, DISTORTION!
Distortion in audio gear varies from low
values (below 0.01%) for Neutral Gear to high values (above 0.1%) for gear
that has a "sonic signature," be it tubes or transistors, with or without
transformers. Vacuum tube gear has a substantial 2nd order
(octave) component that is complimentary.
The link to Article-2 details the evaluation
of the 12A?7 series of dual-triodes, common to all vacuum tube audio gear.
To evaluate, a reference circuit was created with two modes, Low Gain and
High Gain, representing a typical conservative preamp design and a more
aggressive guitar preamp design, respectively. Results ranged from
a low of 0.3% distortion to a high of 2% distortion in the nominal region
for these two circuit variations.
Recording in Retro