Quote
"Timing is an incredibly important cue for the brain, and we know that the ear/brain can resolve down to 4 micro seconds"
[ http://www.head-fi.org/t/702787/chord-hugo/3015#post_10551640 ]
Rob in the phys.org paper linked to in your post it states "The score with the top timing acuity (3 milliseconds)" - so I am wondering about the 4 micro seconds and what is the basis for such a claim. There is a lot of discussion on the Naim forum about the Hugo and the issue of the 4 micro seconds timing came up so would appreciate clarification on this.
We are talking about different types of timing. My understanding is that phys.org paper is referring to the ear/brain being able to resolve pitch with a burst of sound. In this case of 3 milliseconds it was one cycle of a sine wave, and the particular guy could accurately determine the pitch. So it's 3 milliseconds as you need one complete sine wave cycle. Now the timing I am talking about is the inter-aural delay. This is a cascaded set of neurons with data from the left and right ears with lots of different delays - its actually a tapped delay line (the same as taps on a FIR filter!). When a particular neuron gets transient data from both ears at the same time, it fires. So what we have is a method of measuring the timing differences between the ears and measurements of human subjects indicate that the resolving power of this is of the order of 4uS (goes down to 4uS is the term I have seen).
Experiments on cats in the 1950s proved this - they opened up a cat's skull, and managed to probe these individual neurons, and saw different neurons firing with different delays. For human subjects, you can't do this, so you find the delay by adjusting the delay from left to right, and with a delay change you can hear a shift in localisation with a particular test signal. From this one can infer what the inter-aural delay actually is.
Now the inter-aural delay is only used for left right localisation of sounds, and it is an
illustration of the importance of timing. When I use long tap length WTA filters (where I am trying to reconstruct the timing of the bandwidth limited signal perfectly) you do indeed get improvements in left right location of images, but you get a lot of other improvements as well, which are not related to the inter-aural delay. Timing is used in other brain processes too, and we have no understanding about that. Also, even if timing of transients was accurate to 4uS, that does not mean that you can't hear better sound quality with better timing accuracy of 4uS. After all, if I produced a DAC with 4uS of jitter (jitter is timing uncertainty) people would say you would hear that...
What I am trying to get across (and have been doing this since late 1990's with the DAC 64) is that sample rates are important not because of better HF, but because of better timing of transients, and that the interpolation filter is key to reconstructing the timing of the original bandwidth limited signal. With a decent enough interpolation filter then timing is restored, then you no longer need high sample rate recordings - good old CD is good enough.
