With the DEQ2496 test I just posted, I was wondering what happened to
the Transporter in digital loopback mode with that unit connected (but
bypassing the DSP processing). Here's what the digital path looks like
for those unfamiliar:

computer server --> ethernet --> Transporter --> TosLink --> Behringer
DEQ2496 --> TosLink --> Transporter DAC --> analogue (I measured RCA)

Yup, that's 2 runs of TosLink - inexpensive plastic core 6' units (<$20
each) in my test case.

Here's what a 24-bit Dunn J-Test looks like with the Transporter direct
(I used the higher resolution 24/48 signal):
14497

The usual beautiful Transporter jitter plot. The 6 tiny spikes/sidebands
are estimated as <300ps total (I think Stereophile measured 230-270ps) -
nice corroboration!

Now what happens with the DEQ2496 in line?
14498

Obviously quite a bit more jitter has been injected by the Behringer! My
estimate looking at the top 8 sidebands suggests that the jitter level
now is 2ns!

Since I can just turn the digital loop on and off, I can do
instantaneous A-B'ing of the sound. Even in this condition, I cannot say
the clearly increased jitter is at all noticeable. What can I say, Even
knowing this I'm just fine with keeping the DEQ2496 in line and use the
room EQ function since *that* is audible! At least now I can say I've
done an A-B test examining the effect of jitter for myself.

The obsessive side of me now wonders if I should get some good glass
cables, or AES/EBU cables and see if the jitter improves...  Anyone with
opinions on this?


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