I remember the first time I became aware of what we call Listener Fatigue. It was many years ago when there was only turntables, vinyl and most people listened to nothing but tube electronics; solid state was just coming onto the hi fi scene and we are part of that pioneering effort.
I know I've told this story before in this Paul's Post series but it's been a while and perhaps bears repeating.
The year was 1974 and Stan and I were hard at work learning the craft of audio design and refining our first product, the PS Audio Phono Preamp. Originally we used the magnificent Audio Research SP3A-4 preamplifier from Audio Research as our reference phono stage. So much better was this preamp than our best attempt that we were pretty certain we'd never manage to get close using solid state at all. Then along came another preamplifier, theQuintessence, that very closely rivaled the SP3 and not only was it solid state but it used very much the same semiconductors we did. There was hope after all.
We spent a good 6 months trying to understand, mostly by trial and error, what was different between our design and theirs - they measured nearly identical - yet certainly never sounded close. Their sound was a warm, tube sound that we could listen to for hours - while ours had a transistory edge to it that did not welcome long periods of listening. In fact, while our design was significantly better than any other solid state design out there that we had access to, it just didn't welcome you to want to listen to more over a longer period of time.
There really wasn't any terminology back then to describe what we were experiencing but we knew one design, the Quintessence, could be listened to and enjoyed for hours while the second design, ours, made you grow tired and fatigued if you listened too long. Your ears became defensive over a period of a half hour of listening and, in particular, you were not encouraged to turn the level of the system up when you played something really great; the opposite was not true with the SP3A or the Quintessence.
When we finally discovered what the difference was, which turned out to be the way we were biasing the stage (we went more class A), the hardness and glare went away and our so called "fatigue" vanished. Now, for the first time, you were encouraged to turn the level up, to look deeper into the music, to let your ears relax.
The cure required the use of a single resistor in each channel; only a few cents of expense. To find this problem and figure out what to do about it took close to a year of hard work.
This was an extremely valuable lesson - not in how to bias a preamplifier - but that small changes can have a huge impact on making a product listenable or unlistenable over a long period of time.
The true mark of a great piece is the desire to listen more, to be pulled into the music rather than tire of it over time.
Tomorrow we'll look at some more examples that are a bit more up to date.