I have come across is the jitter audibility numbers which used to be thrown around, where more recent studies by Julian Dunn
Sadly Dunn is no longer with us so none of his studies are terribly recent, however in one of his last published papers he acknowledged the Benjamin and Gannon study which placed the thresholds substantially higher and Dunn (and Hawksford too) never did any empirical listening tests.
have revised the threshold down to 15-20ps.
let's face it most double blind tests are set up by audio skeptics
Do you have a citation to back this up or is this just your opinion
who have a vested interest in not making fools of themselves by discrediting the what they have been claiming for years.
Can you give one concrete example of this ?
Double blind testing methodologies are difficult to set up, time consuming
(agreed), and prone to produce null results.
Actually look hard enough and you can find several DBT that produce non null results, even members here have succeeded at differentiating between codecs, filters and even between DACs. Where there is a significant objective difference between stimuli detecting the difference is eminently possible. In fact the rapid switch DBT has been found to be pretty sensitive as Tom Nousaine showed in the "Flying Blind" article.
Even the legendary Meyer and Moran study found non null results on noise levels between high-res and red book (at sufficient gain). Humans have been found capable of detecting a difference of between 0.1 and 0.3 db on single frequency tests or frequency differences of less than 1% .
The issue with tests is whether the difference between stimuli is above or below the JND which is different for the type of stimulus, detecting jitter for instance is easier with a single high frequency sound but much harder in music where masking effects appear. When you look at the jitter sidebands from real measured digital devices it is highly unusual to see distortion products that poke above -100db
I've measured the effect of 10, 30 and 100ns correlated jitter vs no added jitter and the effect is amazingly small , no more than 0.2db at any frequency point point for 100ns ! http://hddaudio.net/viewtopic.php?id=15 - so far from the same test data only one person has been able to reliably detect the 10ns jitter sample this is broadly in line with what B & G found.
In short the effect of jitter is vanishingly small on all but criminally incompetent gear (http://www.stereophile.com/content/mcintosh-ms750-music-server-measurements)
so it is in no way puzzling that DBts show poor human ability to detect jitter !
See also http://hddaudio.net/viewtopic.php?pid=117795#p117795 for what even a relatively cheap DAC can do to remove incipient jitter
Clearly it is not reasonable to expect everyone discussing hifi components to go to this level of trouble, especially when the likely result will not provide any useful data for the discussion.