Vibration-induced distortion via ADAT optical ?

[jermagna]

Troubleshooting a problem I had last night and wondering if anyone here has experienced something similar -

Setup -

Allen&Heath MixWizard
UA Apollo 8 (FW)
Apogee Rosetta 800
MBP

Direct outs on the mixer run to the line inputs of the converters.

Apogee is connected to the UA via ADAT optical I/O.

This setup worked great for the first band. I was recording a live show, so not a lot of room for troubleshooting while the music is happening, but everything sounded great. The second band starts to play, and I start hearing distortion, and I can't track down where it's coming from.

This band is MUCH louder than the first and the bass guitar especially is really booming. My stuff was set up in the back corner opposite where the bass cab was, so I was really getting the worst of it. For a while I convinced myself it was just my headphones or something.

Long story short, on playback, channels 9-16 (coming from the apogees) all have audible distortion. Also, on 9-16 only, there are a few instances of those bad-sync "clicks" - but again, only when the band was playing. The distortion isn't there in between songs and it's at its worst when the band was loudest.

Has anyone ever experienced anything like this? It really seems like the vibrations in the room were messing with the Apogees, or the UA's ability to receive the optical signals from the Apogees.

Wondering if holding the optical connectors in more tightly somehow could help? Shock-mounted rack? Don't record loud bands? I hope it's not the Rosetta itself being susceptible to vibration...

[kslight]

Without sound samples it's hard to say, it sounds like a clocking problem though. I have recorded many live concerts using a Alesis HD24XR, with the ADAT outs simultaneously going into an M Audio Lightbridge and Dell laptop, using a TI chipset FW express card, 24 tracks at 24/48. I have had one or two incidents where it would suddenly stop recording to the HD24XRs hard drive itself probably due to vibration...so I installed rubber grommets used for isolating the hard drive vibration from the chassis in a silent computer setup, and also set it up to record to my computer at the same time for redundancy. I make sure the computer is doing nothing else, max buffer setting, and the Alesis is the master clock via ADAT. Everything is installed in a cheesy gator rack...not shock mount.


As long as your toslink plugs are snapped in I don't see how vibrations could affect them. I would check your clock settings, maybe do a few dry runs at home to see if you can recreate the problem over time.

[jermagna]

"as long as your toslink plugs are snapped in" - thanks for mentioning that!!

I have only set up a couple of rigs involving this kind of connection - and I do remember that I once used cables that were very thin and light, and the connectors clicked in a satisfying way. This time, I'm using cables of a different style and they don't really snap in to the jacks in the same way. I will try to hunt down some of the lighter style cables. They only need to be like 6" long ... just being shorter and lighter would help with the strain relief ... again, if that's what is really causing the problem!

I did a test recording at home and everything was solid clocking-wise - and the first band's set had no problems at all - that's why I'm hung up on this vibration thing ...

[kslight]

I don't remember where my last toslink cables came from but they are solid. If they are snapped in I don't see how vibrations could effect it, but if they are loose then a momentary disconnection (caused by vibration or movement?) could cause clocking errors that would sound like you describe.

[Snarl 12/8]

Have you tried slapping things during recording to see if you can cause the problem via "vibration?"

[jermagna]

Have you tried slapping things during recording to see if you can cause the problem via "vibration?"

Next chance I get, I am going to attempt to recreate the problem by cranking a bass cab in the room with a tone generator sweeping low frequencies ...

[Snarl 12/8]

That seems like a lot more work *and* not as foolproof as my method, but to each their own.

[mrc]

If you haven't had your connectors covered when not connected, both male and female, try blowing them with dry, oil-less compressed air. Inspect the ball and cups for damages to the surface. Good light and optical assist.