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[Peter Weihe]

Warning!

Yesterday I wanted to check the latency of my Lavry Gold converters with Logic 8 software running on the Digi Core engine of my PT HD 3 on an Intel Mac.

I played a sine wave through the Lavry Blue DA and recorded it back through the Lavry Gold.

The polarity of the recorded sine wave was switched.

Ok, some older Lavry Gold converters have pin 3 hot and you can switch polarity in the menu. Also the Lavry Blue has a polarity switch. Fist I thought that I had one of the settings wrong.
I repeated the recording  several times with different settings and the polarity was switched according to the settings. All switches worked properly.

Then I made the same test with Pro Tools 192 I/O converters and again the polarity was switched.

I repeated the test with the Pro Tools 8.1 software and the polarity of the recorded sine wave was correct with all combinations of converters in my normal settings.

So, Logic switches the polarity while Pro Tools doesn't with the same Setup.

I wrote a mail to warn some of my friends and asked them to perform the test. One of them just called me and confirmed that he found the same problem with his new HD Native System on a brand new 12 Core Mac with 192 I/O converters and the Pro Tools 9 engine.

So this obviously seems to be independent from the hardware configuration.

????????????????? Well........

We don't know whether it happens on the way in or out.

Peter

[KB_S1]

Peter,

I will do a test on Friday when I am back in the studio.

PT 8.1 - HD2 - MacPro 10.5

Logic of some sort, can't remember as i never use it.

[Spindrift]

Forgive my ignorance:  What are the real-world ramifications of this if it turns out to be the absolute case?

I know there is equipment out there in use that is wired Pin 3 HOT (Tascam DA-30 DAT deck for example) that some engineers don't know about...What is the end result?

If a record is mixed to a DA-30 with Pin 3 still wired HOT, when a kick drum pounds, will the end-listener's woofer have negative excursion vs. positive? Or is it usually caught at mastering? Is it ever really a problem?

[Fibes]

Spindrift wrote on Mon, 10 January 2011 19:00

Is it ever really a problem?

Yes it is, all absolute polarity arguments aside when I order something it should do what I want not what it feels like.


This makes no damn sense to me but simultaneously isn't a surprise.



I just got into it with someone that makes a boutique channel switching amp that flips on channel B. This makes multi amp recording tricky.

[Spindrift]

Fibes wrote on Mon, 10 January 2011 16:20

Yes it is, all absolute polarity arguments aside when I order something it should do what I want not what it feels like.

Well, yes, if you're buying something, it should be phase accurate.  But aside from that....

I just did some reading on Absolute Phase and it appears to be a can-of-worms. Sorry, I don't mean to de-rail this thread with that stuff.  Nevermind!

[arconaut]

We got into absolute polarity here:
http://recforums.prosoundweb.com/index.php/mv/msg/31977/0/0/ 2239/

Other places too, I'm sure.

That is a very interesting observation, I'll have to see if I can reproduce it on one of our systems.

[Nicky D]

Weird

And not cool at all.

[KB_S1]

I am working on an album just now that has been mostly live takes of drums, bass and guitar. Overdubs of more guitar, lead vocals and other things.
It is now going to the producers home studio for the twinkly details but he is running logic. It may then come back to me on the PT HD rig.
It will be interesting to see if it causes any problems.

[arconaut]

Hi All,

Okay, I have PT 8 and Logic 9. Converter is a Digi 192.

Created a PT session at 192kHZ with two mono tracks.

On track 1: Generated a 500Hz sine for 30 seconds using SigGen. The interface output was patched into input 2 and recorded. This yielded this result:



You can see some latency, but the polarity of the wave is intact.

Next, I opened Logic and created two tracks in a 192kHz session. Dragged my audio file from ProTools (created using SigGen) into Logic, did not move any patches or change anything. I did make sure that I was using discrete ins and outs in both Logic and PT.

Looks like I can only insert one image per post, so next post shows greater latency but also flipped polarity.

[arconaut]

So, much more latency here but also polarity reversal!

[arconaut]

I wonder what happens if you use the built-in I/O on the Mac. Or is there another way to determine whether CoreAudio or Logic is accountable?

[marcel]

Has anybody reliably eliminated the possibility that the interface (not physical, but software) between PTHD and CoreAudio is to blame for this stuff?  Will, say, GarageBand or Cubase produce a similar result?

[marcel]

Noah:

Not to derail, but what's with the +/-22ms of latency in the Logic session?

[arconaut]

I'm not sure, maybe it's a buffer size setting needing adjustment in Digi Core Audio?  Looks like it might be maxed out at 2048? Maybe the latency could be improved, but would it affect polarity?

[Peter Weihe]

Hi Noah,

thanks for performing the test and posting the screenshots.

arconaut wrote on Wed, 12 January 2011 01:27

I wonder what happens if you use the built-in I/O on the Mac. Or is there another way to determine whether CoreAudio or Logic is accountable?

I informed the German support team from Avid and they will check whether the Digi Core engine is accountable.

Is the Core driver for HD Native the same as for HD?
I ask because the polarity switch also happens with Pr Tools HD Native and Logic.

Peter