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  #1  
Old 03-12-2013, 10:34 AM
dwaynedelario dwaynedelario is offline
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Default Trim Optical Inputs on OMNI?

I just set up my Mac Pro to send system audio via Optical/SPDIF and I am getting clipping on the inputs of the OMNI when I play mastered tracks from Quicktime. Is there a way to trim these? Seems that lowering the volume in the hardware mixer window is just that: volume only. I have "Sample Rate Conversion" checked... am I missing something?

Surely I can reduce the volume in Quicktime/iTunes etc, but that seems a bit ghetto
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Old 03-12-2013, 10:49 AM
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Default Re: Trim Optical Inputs on OMNI?

If a digital signal is clipping at the input of the omni, wouldn't that mean it's actually clipping before the signal reaches the omni?

Ghetto or not, I think the correct place to adjust volume is at the source in this situation.
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Old 03-12-2013, 10:56 AM
dwaynedelario dwaynedelario is offline
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Default Re: Trim Optical Inputs on OMNI?

Thanks John, that's what I figured but thought it was worth asking. So basically every album mastered in the last 15 years needs to be trimmed in order to listen properly.
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Old 03-12-2013, 12:10 PM
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Default Re: Trim Optical Inputs on OMNI?

Something seems wrong if that's the case. Are you 100% sure that what you are hearing is actually clipped audio? (i.e. if you record it, you can see clips in the waveforms at the transients?).

If so is there an EQ activated in iTunes that might be boosting the levels?

Also, just looking at audio MIDI setup app, there are settings there for volume, and also for bit depth of the mac's built in output. If the volume is turned up there, that might explain why you need to reduce it in any apps that are using that output.
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If a MIDI event triggers a sample of a tree falling and there's no one there to hear it, does it make a sound?
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Old 03-12-2013, 12:14 PM
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Cliffy_Boy Cliffy_Boy is offline
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Default Re: Trim Optical Inputs on OMNI?

if I'm not mistaken, the red clip light on the Omni activates at 0dB so it may not necessarily be clipping, just hitting the ceiling - which most mastered songs do.
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Old 03-12-2013, 10:13 PM
dwaynedelario dwaynedelario is offline
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Default Re: Trim Optical Inputs on OMNI?

That's what I was hoping for Cliffy, but there is definitely distortion going on.

John, I haven't used iTunes yet, just Quicktime to send audio... so no EQ or anything like that. I always turn those settings off first thing anyway. There was no volume boosting in the AMS panel either. Theoretically, there should not be volume control on the Mac side for optical outputs, correct?
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Old 03-13-2013, 03:25 AM
Neil Pickles Neil Pickles is offline
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Default Re: Trim Optical Inputs on OMNI?

Quote:
Originally Posted by dwaynedelario View Post
Thanks John, that's what I figured but thought it was worth asking. So basically every album mastered in the last 15 years needs to be trimmed in order to listen properly.
Most (not all) modern "loud" masters are in fact clipped.A casualty of the loudness wars sadly. If you push something that hard to get it that loud it's virtually impossible to avoid true peak clipping.

Huge commercial artists.....all clipped.

Trimming will not remove the clipping that is there at source.

I've started browsing second had stores for old pre "new new remastered" CDs as generally the remasters are ruined going for modern volume.
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Old 03-13-2013, 09:16 AM
dwaynedelario dwaynedelario is offline
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Default Re: Trim Optical Inputs on OMNI?

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Originally Posted by Neil Pickles View Post
Trimming will not remove the clipping that is there at source.
Thanks Neil. While I appreciate the sentiment, I am aware that pulling down a volume knob won't eliminate any sample clipping in a source, but this is slightly beside the point (I was only poking fun at loudness wars above). Without having to make any volume adjustments on the Mac, I should be able to monitor a master quality recording through the optical port of the OMNI and not hear any distortion, clipping or no clipping at the input side. That is to say, should it not just be a digital transfer, at least in theory?

Perhaps this is a bit depth issue. I thought I remember reading that S/PDIF uses a 20bit protocol, and the settings in AMS seem to default to 24bit. Could there be some kind of faulty bit slip going on at the receiving stage?

For now I am going back to analog monitoring from the Mac as I realized that selecting Optical S/PDIF in the hardware menu sacrifices all the ADAT inputs. Which is really unfortunate. Guess I have to keep that last 192 around after all.
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Old 03-13-2013, 09:42 AM
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Default Re: Trim Optical Inputs on OMNI?

SPDIF is capable of 24bit, that should not be an issue.

However, my mac has a setting for outputting 32bit float point, 24 bit fixed point, 16 bit etc.

I'm not sure why a digitally mastered recording that does not audibly clip in other situations would clip in this situation, unless you were outputting it from the mac at a higher bit depth than you were receiving it at without using dither.

Or, the distortion you are hearing is caused by a clocking issue. If the mac and the Omni are both set to be master clocks, you will definitely hear a difference. One of the problems with built in sound is that a lot of computers can't be set to slave to an external source. If this is the case, you'd need to have the Omni slave to the incoming SPDIF signal from the mac. If you end up having to make the mac the master clock, you obviously would only ever want to use your mac as a clock master when you absolutely had to. Otherwise, hopefully you can take another optical cable, and connect the SPDIF out from the Omni to the SPDIF in on the mac, and see if you can set the mac to slave to the Omni in Audio MIDI setup.
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If a MIDI event triggers a sample of a tree falling and there's no one there to hear it, does it make a sound?
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  #10  
Old 03-13-2013, 10:41 AM
nst7 nst7 is offline
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Default Re: Trim Optical Inputs on OMNI?

Dwayne,

There's another option to try, that will free up your Adat inputs. On Amazon, you can get a Spidf Optical to Coaxial converter for $12. I don't know how to link to it on my Iphone, but you want the one that's Optical in, Coaxial out.

That way you can set the digital setting of the Omni back to Coaxial, freeing up your optical in to be Adat again. And still getting the benefit of having your Mac's audio come through the Omni's D/A conversion.

And I'm pretty sure you can set the Mac Pro digital out to be clocked externally.


Keep in mind that for recording purposes, the Omni is still a max of 8 channels in. So you could have 4 channels of analog and 4 channels of Adat, with the audio coming in the Spidf not taking away any of that, because it's using the mixer function.
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