Hi All,
Stumbled on to this thread and while a bit dated thought I'd share some thoughts as the designer/manufacture of the Tortuga LDR preamps.
I've read the neurochrome.com report with great interest as you can imagine. An impressive piece of work and I mean that sincerely. A bit amazed that the author took all that time and effort but nevertheless top notch work.
I could quibble around the edges about the report but I really don't dispute the overall arc of the results. I mean it's measurement after all. Either you measured it right or not. One clarification worth noting is that the report was done on our older V2 model board which was replaced with our V25 design which has significant changes over the V2. The V2 had some unfortunately noisy op amps in the design which are gone in the V25.
But my main point regarding the report isn't that it's factually incorrect or technically flawed. It's that it's lacking in perspective. Most discussions here and elsewhere starts with an implicit premise that ANY level of measured distortion is discernible to the human ear and that therefore a few points less distortion means something sounds better than a few points more distortion. So we chase specs and measurements and are impressed when the specs are better and the noise measurements are lower.
But does lower distortion really matter? By that I mean can you actually honestly really tell the difference when you're listening to music? Human ears/brains are not distortion measuring devices. Below a certain threshold level we can't hear the distortion. Yes, it's there! You can measure it. But so what? I've dug into this topic and while you can ALWAYS find a few exceptions the vast majority of scientific studies on the ability of human beings to discern distortion conclude that anything ~1% or less can not be detected by the human ear. Can you find someone somewhere who claims otherwise? Of course you can. But the consensus is that it doesn't matter below a certain threshold and that threshold is WAY above most measurements.
So yes, you can argue that LDRs are inferior attenuation devices because of their higher distortion characteristics compared to the other technologies. Yet, when you build an LDR based attenuator and actually listen to it your human experience of that moment tells you you like what you're hearing. And then along comes a smart engineer with sophisticated measuring equipment and tells you you shouldn't like it and that you're being fooled.
If measurement was the definitive metric of how good something sounded we'd test every audio component, rank them by test results, publish the results and then buy the equipment with the lowest distortion we can afford. And we'd put every bottle of wine through a similar process and only buy the one with the best specs. And we'd put every car on a dynomometer and buy the one with the best performance. But we don't do this. Not because measurements aren't useful (especially to engineers in the design process) but because beyond a certain point, the measurements don't matter and are not definitive proxies for the human experience.
Nelson Pass said it best....“The ear is not a microphone, the brain is not a tape recorder, and measurements are limited in describing subjective quality. I like to have low distortion and so on, but these things take a back seat to what I experience when I listen. There are plenty of products which have great specs – I will not be offended if you buy those.”
Peace,
Morten
Uh huh