OMNI Software Mixer Problem

[Darryl Ramm]

Are we talking TOSLINK or coaxial S/PDIF? Presumably real TOSLINK S/PDIF from the Mac, but then there can't be DC offset on TOSLINK (i.e. the optical cable thingy) as there is no DC connection.

Are you sure the TOSLINK input being used is set to S/PDIF not ADAT?

I would try debugging things by trying a TOSLINK to coaxial S/PDIF converter into the Omni.

[vieris]

Yes TOSLINK/Optical S/PDIF. It's giving symptoms like a DC offset whatever the case may be, low frequency oscillation, bit-stream error, something is odd... I'm trying to figure out if its the mac output or the omni input. I have the omni SRC active to avoid clocking errors.
I'm about to try putting a box inline with the signal. TC3000 or something in bypass to help isolate\troubleshoot.

[Darryl Ramm]

Originally Posted by vieris

Yes TOSLINK/Optical S/PDIF. It's giving symptoms like a DC offset whatever the case may be, low frequency oscillation, bit-stream error, something is odd... I'm trying to figure out if its the mac output or the omni input. I have the omni SRC active to avoid clocking errors.
I'm about to try putting a box inline with the signal. TC3000 or something in bypass to help isolate\troubleshoot.

Cool, still try a converter to coaxial if you can as it excludes the input TOSLINK.

And cables, I hate bloody TOSLINK cables and snap-in connectors... (but that is usually no signal or horrible dropouts).

[tklaavo]

We have also this "digital DC offset" problem with a 2009 mac pro -> optical out -> Omni. We can see it in Omni input meters, and it can be recorded to PT. Straight line, looks like it's outputting a steady number other than zero.

However, if I play anything through the optical out, the problem disappears. I have a dummy audio file on the desktop which I can preview by hitting spacebar, and problem is solved. I do this every time I boot the system.

Tuomas

[dwaynedelario]

Tuomas.... I am still having the exact same issues you describe. Have you ever found a solution???

[Ray JB]

Like Darryl's suggestion, my setup take the TOSLINK optical, converts it to SPDIF thru a small converter and then that goes into the SPDIF input of an MBOX Pro which is in standalone mode. I have the MBOX set to clock to the incoming SPDIF. This then goes to my OMNI SPDIF input, with SRC on and the input on the hardware page set to unity.

This gives me the great bonus of being able to use the MBOX Pro as a SPDIF volume controller, very handy if you run a calibrated system with a "chalked off" monitor level (79dB for me as I work on film stuff in near-field). If I don't have the ability to attenuate the computer output you can get a real surprise when iTunes or Spotify or other standalone audio apps are played at full scale thru the system....ie: crushingly loud.

Before when I used to run in straight Optical to the OMNI, I had the same strange issues as the others describe, motor boating or low level weird stuff playing when nothing should be there....

[Frank Kruse]

Originally Posted by tklaavo

We have also this "digital DC offset" problem with a 2009 mac pro -> optical out -> Omni. We can see it in Omni input meters, and it can be recorded to PT. Straight line, looks like it's outputting a steady number other than zero.

However, if I play anything through the optical out, the problem disappears. I have a dummy audio file on the desktop which I can preview by hitting spacebar, and problem is solved. I do this every time I boot the system.

Tuomas

I've had this for years. DC coming in from optical MacPro out via converter.

This is not an Omni issue. I have the same thing with an 8x8x8. The DC is coming from the Mac Optical out.

I usually get this after starting the computer in the morning. You can go to the OSX audio setting, then to the notification signals setting and manually play any of the error tones once. This will stop the DC immediately. From then onwards it doesn't come back for the rest of the day.

I haven't found a way to stop this. Could be a hardware thing since over here it only seems to happen after a cold start of the Mac. But I've seen this on many many cheese grater macs with different OSX flavours.

Frank.

[dwaynedelario]

Thanks for the suggestions all. I am simply going to do what others seem to be doing, which is playing a dummy audio file with my monitors muted on the desktop right at bootup (it makes a loud pop at first). Seems to be totally fine after that.

@Ray JB: I like the idea of having fader gain for the optical input, but I don't think I am going to run out and pick up and Mbox just for that purpose :)

To be honest, all of this nonsense with the digital output of the Mac is making me think I'l just go back to analog with a well shielded Y cable!

[Peter Baird]

I've had this since getting an OMNI--my hunch is it's related to sample rate conversion. OMNI seems to do this whenever the system has been freshly booted. For me the fix was always very simple: play a song (either iTunes or direct from the Finder), experience the big THUMP on the left channel, and then work as normal.

Just booted the system for today's fun. Exact same thing--weird distortion on the left, play a couple of seconds of the Johnny English soundtrack on iTunes, all better.

Peter

[TVPostSound]

When using Toslink through the Omni mixer, disable it in the hardware input.
Protools will not then clock to it.
I have no issues that way.