I do think there's some truth in the idea that it's a perceptual, not a technical issue; for example take a look at the recent work Earl Geddes has done on the relative unimportance of THD% in perception of speaker quality.
It's still one of those issues where we are measuring the wrong things to describe how we may perceive 'quality'. THD% tends to be a discrete-time measurement, a method which our hearing does not reflect; human hearing is a system that takes subsequent developments into account, cued by the initial transient (Google 'Haas integration time'). That's an effect of the profound software (wetware) filtering the ear/brain system uses, and which we just don't understand the full complexity of. For example, the ear mechanism itself is a lousy transducer, running out past 30%THD at modest levels, even physically emitting its own tones; but humans can still resolve 140dB of dynamic range, the difference between distortion spectra for the same nominal %thd, and even 1-3 microsecond delays between channels, equiv. to angular direction-finding with resolution better than 5degrees. Useful stuff for the primitive savannah hunter we once were... But being a higher function in the brain, it is also profoundly, demonstrably influenced by our other sensory inputs and (fugitive) memory - lots of cross-talk
Cheers
M.
THD, which I accept benefits from a thorough drill-down, can be difficult to detect
in isolation but becomes perfectly audible when you compare something with high levels, say 16% in the case of the cartridge, with something running at around 0.1% - even if the latter is comprised solely of the nastier harmonics.
Speakers are a great example actually. Many have high distortion yet sound fine in isolation, yet these distortions become very obvious when you compare to a much cleaner driver such as a good electrostatic.
However, getting back to vinyl we have:
- Motor/electrical noise
- Speed instability
- Acoustic feedback
- Double digit cartridge THD - (from the best!)
- Response variability - both intrinsic errors in the cartridge and often the RIAA stage but also scanning loss which progressively rolls down HF across the LP side.
- Distortions introduced by errors with arm geometry.
- VTA errors introducing errors on L/R images.
- High noise floor.
- TT and arm resonances - the cartridge is effectively operating while bolted to a complex resonator.
- Wear variability - more plays = more more noise and reduced HF
- Chanel separation which hovers around 30db at best, and collapses entirely as you approach tip mass resonance.
Am I selling this pinnacle of audio faithfulness to anyone yet?
All vinyl front ends suffer from the above with of course a different mix for each case. However many of them transcend the ultimate quality of the front end as they are fixed limitations of the mechanical process.
Given that list its a wonder vinyl sounds as good as it often does - and it does, I use it and enjoy it. But please people, don't pretend that it competes with clean, modern digital if faithfulness is your aim.
