Strange difference between Adat A and B (2nd gen)

[astroman]

Took me a while to re-activate my Win7 license, but finally it‘s a fresh install with as few additions as possible to have a lean Scope system.
While connecting gear to the Adat ports I noticed a strange performance of the Pulsar 2: port A no problem, but when adding something to port B, occasional crackling set it.
Not a complete failure of transmission, just a bunch of glitches roughly in 15 second intervals.
When I connected the offending Adat client to port A of the next Pulsar 2, everything was fine again.
(I used the exact same gear, just plugging the TOSLink cables into the next card)

IIrc Adat B on 1st generation cards is critical, but never expected 2nd generation cards to perform kind of similar.
Scope is clocked by a Mutec MC7 via Syncplate BNC, as is the Digidesign Adat Bridge and MPC4k, only an Audient ID22 is set to slave from Adat.

No complaints, though, atm everything runs fine, but background info would be much appreciated.

ps: another thing that puzzled me was null-tests to measure latency (on Adat ports) never fully nulled, but left an almost identical replica of the source, just about -65dB lower in level.
(I used a file as source, played from DAW via Asio into Scope, then sent to the external unit and back, no conversion involved)


cheers, Tom

[valis]

ADAT B crackles on both cards?

The null issue is because they probably take separate paths through scope and have a time offset of 1-2 samples. This is expected, and so think of using the ADAT ports in groups of 8 where nothing that requires phase coherence overlaps between digital or analog I/Os without compensation (phasefix from Adern can do this).

[astroman]

The setup was the most simple one: Adat ports to DynamicMixer, PhaseFix in the source path, mixer to monitor.
On the target side there was just the DAW sending back unprocessed.
I only watched the main output, but your hint triggers the idea of insterting a couple of Channels to have meters on input, too.

The thing that confuses me is that null tests (back in that infamous era ) always ended in perfect zeroes once PhaseFix hit the spot.
At least with digital signals, on analog gear there was of course a tiny difference close to noise floor.
My suspect was that old ProTools may package only 16 bit of data into the stream, but actually the difference from the MacMini M1 (set to 24bit) is greater.

Null signals in 24bit (lifted 60 dB in the DAW) showed no audible difference to the source.
The roundtrip of sensitive analog sources also revealed no flaws, so signal integrity seems ok and with 1 card for each 8-group of channels no more glitches for hours yesterday, cool.

1 bad result: those high quality BNC cables I bought for PT don‘t fit the old connectors (sitting kind of shaky).

[valis]

Then the offset is greater than 1-2 samples.

Use a micro mixer with phase lock enabled when testing, reduces variables.

[nebelfuerst]

Back from my ADAT days, I remember similar impressions. There was a difference between connecting only one or both Adat-pairs to the A16. My theory was that one path provides bad synchronisation, which also affects the other part. This mostly happened on the input-path to scope.
It suddenly dissappeared when buying HQ cables. Now I use Zlink which also never crackled.
The period of crackles was constant over short time, but not over long times. It was 1/5minutes to 1/20sec.

[Bud Weiser]

I´m also using Z-Link w/ A16Us.
Good to know it´s better than ADAT.
I wonder why the OP´s issue happens when using a Mutec-MC7 masterclock though.
It´s a precise device.
Can it be the ADAT cables only?

How to recognize better quality of ADAT cables when buying?



Bud

[dante]

How to recognize better quality of ADAT cables when buying?

Bud

The price

Diamond Optical

Diamond Optical Cable.jpg (31.6 KiB) Viewed 8392 times

[nebelfuerst]

HQ cables have more precise plugs, sometimes recogniseable by not beeing build from one kind of plastic for the whole part.
The optical end should also be a cleaner cut, but that is hard to see.
Unfortuately, there no tool to read the error-rates from a receiver on the scope/xite.
There are measurement devices for optical power, but buying such a device for checking Adat cables is just a deal for rich people.

@dante:
for "diamond optical" you should't go without the suitable iphone app:
https://en.wikipedia.org/wiki/I_Am_Rich

[Bud Weiser]

The price

peanuts !



Bud

[Bud Weiser]

HQ cables have more precise plugs, sometimes recogniseable by not beeing build from one kind of plastic for the whole part.
The optical end should also be a cleaner cut, but that is hard to see.
Unfortuately, there no tool to read the error-rates from a receiver on the scope/xite.
There are measurement devices for optical power, but buying such a device for checking Adat cables is just a deal for rich people.

o.k., then it seems to be trial ´n error.



Bud

[astroman]

I wonder why the OP´s issue happens when using a Mutec-MC7 masterclock though.
It´s a precise device.

Simply because OP is too stupid to setup a 5 items routing window properly
The Adat lines between Scope and PT now both work as expected and null as in the old days.

On the MacMini it‘s different, it‘s the only device not clocked by the Mutec and can be Adat slave only (ID22).
This seems to work perfectly, though.
I located the minimal loudness position by PhaseFix and recorded 3 loops of the not fully extinguished signal, normalized the track to -6dB, made an inverted copy of the 1st loop and placed it on another track precisely above the 2nd loop.
The mix of the 2 tracks resulted in perfect zeroes.
(recording in PT via Adat 1 while the Mini/ID22 was playing the loop on Adat 2, so both Pulsars engaged and click free)

Btw I did a similar test with PT receiving clock by a high end BNC cable and the result was kind of flanging, lfo modulated.
(when closing the BNC ring it definitely doesn‘t feel tightened)
The current cable seems to work flawless, but has unknown age and I had to shorten it due to Digidesign‘s 256xSuperclock, that‘s why I’d rather replace it by a proper one. At least it‘s from a pro studio installation.

Thanks @nebelfuerst for mentioning the (blue) A16 performance. I would have expected right the opposite if 1 unit uses both ports.
(my own A16 is disassemled, waiting for repair...)

Atm I can get along with the ID22, but would prefer an USB double Adat or Adat/spdif box.
In that case I could use one of those lines from the Mutec to keep it synced permanently.
(the ID22 sometimes gets nuts when it‘s sync source is switched off)

[valis]

PT clock fluctuation is due to poor signal (which you surmised and changed cables for, I believe) and what is likely a PLL chip (phase locked loop) to try to stabilize bad clock. Think “slew rate limiter” from modular…

[astroman]

Yes, PT‘s „Superclock“ (256 x sample Frequency) is a kind of nightmare ... and the only way to externally clock a Mix24 system. I‘ll probably exchange the > 20 years old connectors instead of getting other cables.
(but at least everything seems to work right now and I can use Scope again)