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Author Topic: Logic with Pro Tools Hardware switches polarity  (Read 20587 times)

Peter Weihe

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Logic with Pro Tools Hardware switches polarity
« on: January 10, 2011, 03:00:47 PM »

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





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Peter Weihe

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #1 on: January 10, 2011, 06:19:47 PM »

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.
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Re: Logic with Pro Tools Hardware switches polarity
« Reply #2 on: January 10, 2011, 07:00:00 PM »

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?
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Fibes

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #3 on: January 10, 2011, 07:20:12 PM »

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.
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Spindrift

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #4 on: January 10, 2011, 07:49:26 PM »

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!
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arconaut

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #5 on: January 10, 2011, 11:14:34 PM »


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.
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Nicky D

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #6 on: January 11, 2011, 09:36:56 AM »

Weird

And not cool at all.
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KB_S1

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #7 on: January 11, 2011, 10:49:53 AM »

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.
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arconaut

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #8 on: January 11, 2011, 02:59:38 PM »

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:

index.php/fa/16143/0/

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.
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arconaut

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #9 on: January 11, 2011, 03:01:18 PM »


So, much more latency here but also polarity reversal!

index.php/fa/16144/0/
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arconaut

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #10 on: January 11, 2011, 07:27:30 PM »


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?
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marcel

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #11 on: January 11, 2011, 09:35:19 PM »

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?
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Re: Logic with Pro Tools Hardware switches polarity
« Reply #12 on: January 11, 2011, 09:38:17 PM »

Noah:

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

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #13 on: January 11, 2011, 11:00:20 PM »


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?
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Peter Weihe

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #14 on: January 11, 2011, 11:29:45 PM »

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



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Peter Weihe

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #15 on: January 11, 2011, 11:35:39 PM »

marcel wrote on Wed, 12 January 2011 03:35

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?


A further test with Cubase and Digi Core would help to find out.
Has anybody access to that combination?
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Peter Weihe

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #16 on: January 11, 2011, 11:46:35 PM »

marcel wrote on Wed, 12 January 2011 03:38

Noah:

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


arconaut wrote on Wed, 12 January 2011 05:00


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?


With my HD/Logic setup latency is roughly about 2 msec higher with Logic than with Pro Tools with the lowest buffer size setting for Logic.

As the polarity switch was observed in three different systems now, your's and my HD
setup und the HD Native setup of my friend each with different buffer size settings
I believe that it has no influence on the problem.

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Peter Weihe

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #17 on: January 11, 2011, 11:57:19 PM »

KB_S1 wrote on Tue, 11 January 2011 16:49

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.


Probably not as long as he's keeping it in the box.
As soon as he would leave the digital world, sent a signal out through the DACs in order to process it with analogue gear and record it back through ADCs it would be polarity reversed.
However that would probably only be the case if he used the Digi Core driver.

We have not found out yet, whether the same would happen with a Logic/Symphony
system. But that is hard to believe.


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Peter Weihe

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #18 on: January 12, 2011, 12:16:40 AM »

Spindrift wrote on Tue, 11 January 2011 01:00

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?



There is a AES paper by Milton and Greiner about a number of experiments about the audibility of acoustic polarity:

You can find it here:

http://www.aes.org/e-lib/browse.cfm?elib=6950

"AES E-Library
Observations on the Audibility of Acoustic Polarity

A number of experiments are described which show that absolute acoustic polarity is clearly audible in certain select cases of reproduced sound from acoustical instruments. The nature of the audible differences and the characteristics of the temporal signals which lend themselves to audibility are described. A large double blind listening experiment using varied musical program material is described as well.

Authors: Greiner, Richard A.; Melton, Douglas E.
Affiliation: University of Wisconsin Electroacoustics Laboratory, Madison, WI
JAES Volume 42 Issue 4 pp. 245-253; April 1994 Import into BibTeX

Click to purchase paper or login as an AES member. If your company or school subscribes to the E-Library then switch to the institutional version. If you are not an AES member and would like to subscribe to the E-Library then Join the AES!

This paper costs $20 for non-members, $5 for AES members and is free for E-Library subscribers.

Learn more about the AES E-Library

E-Library Location: (CD aes5)   /jrnl8997/1994/8531.pdf"
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Peter Weihe

arconaut

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #19 on: January 12, 2011, 08:01:58 PM »

I tried to chase this down a bit more today but was really short on time. But I'll recap what I did do - created an audio file again using Signal Generator. I played it out of Pro Tools 8 and patched the output of the 192IO directly into a tie line to another room.

In the second room, I created a Pro Tools session and recorded the waveform being fed from the other room. Polarity remained intact. This was into a 96IO using PT8.

Returned to the "source" room and imported my waveform file into iTunes, which plays through the 192IO via DigiCore Audio. Then recorded this file to a second track in the other room. Again, polarity remained intact.

Then... I ran out of time. Next was to launch Logic on the receiving end and see if there was any difference there and after that to have Logic as the source via CoreAudio and Pro Tools recording once more. Eventually, the culprit will make itself known.

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Peter Weihe

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #20 on: January 13, 2011, 04:00:40 AM »

arconaut wrote on Thu, 13 January 2011 02:01

I tried to chase this down a bit more today but was really short on time. But I'll recap what I did do - created an audio file again using Signal Generator. I played it out of Pro Tools 8 and patched the output of the 192IO directly into a tie line to another room.

In the second room, I created a Pro Tools session and recorded the waveform being fed from the other room. Polarity remained intact. This was into a 96IO using PT8.

Returned to the "source" room and imported my waveform file into iTunes, which plays through the 192IO via DigiCore Audio. Then recorded this file to a second track in the other room. Again, polarity remained intact.

Then... I ran out of time. Next was to launch Logic on the receiving end and see if there was any difference there and after that to have Logic as the source via CoreAudio and Pro Tools recording once more. Eventually, the culprit will make itself known.




Wow Noah, thank you for your effort!

That's a brilliant test method and you are right, the culprit will have to leave his hiding.

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Peter Weihe

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #21 on: January 13, 2011, 04:00:20 AM »

Sorry, Double post.
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Peter Weihe

arconaut

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #22 on: January 13, 2011, 11:39:24 AM »

Further snooping, here are a bunch of images. I generated a waveform and patched from the 192 IO output 1 into a tie line. Then I did the following things:

1. Recorded the waveform into ProTools on the 2nd system first using Pro Tools for source playback, then using iTunes via DigiCoreAudio for playback.

2. Recorded the waveform into Logic on the 2nd system, again using ProTools and iTunes for playback.

3. Recorded the waveform into ProTools again, this time using Logic and iTunes for the source.

Here is a shot of the original waveform:

index.php/fa/16148/0/
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arconaut

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #23 on: January 13, 2011, 11:41:25 AM »

Here is a shot of ProTools, showing polarity remaining intact whether playback comes from ProTools (from source system) or from iTunes/CoreAudio:

index.php/fa/16150/0/
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arconaut

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #24 on: January 13, 2011, 11:42:57 AM »

Next we have Logic as our recording platform, and you can see that using both PT and iTunes as the source, the polarity is now flipped.

index.php/fa/16151/0/
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arconaut

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #25 on: January 13, 2011, 11:45:53 AM »

One more - this is recording into PT while using Logic and iTunes for source playback. Again, polarity is ok.

index.php/fa/16153/0/

So the issue seems to be on input. But still, we don't really know if the issue is with Logic or with CoreAudio. For this, we'd need to eliminate CoreAudio.

But that's all the time I can dedicate to this for now!

Noah
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Peter Weihe

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #26 on: January 13, 2011, 01:02:51 PM »

arconaut wrote on Thu, 13 January 2011 17:45

One more - this is recording into PT while using Logic and iTunes for source playback. Again, polarity is ok.

index.php/fa/16153/0/

So the issue seems to be on input. But still, we don't really know if the issue is with Logic or with CoreAudio. For this, we'd need to eliminate CoreAudio.

But that's all the time I can dedicate to this for now!

Noah


Hi Noah, thanks again for your thorough test.
I can confirm the result.

I imported the sine wave from my test into I-tunes on a second Mac.

1. I recorded the output from the second Mac into Pro Tools on my Studio Mac and the polarity stayed intact.

2. I recorded the output from the second Mac into Logic ( with Digi Core) and the
polarity was switched.

You are right. The polarity Switch happens on the way in.

I asked some friend to perform the same test with a Logic/Symphony system.

3. Christoph played a sine wave from Logic trough the Symphony system with Apogee 16x DA converters and recorded it back into Logic with Apogee 16x AD.

The polarity stayed intact.

4. Then he imported the sine wave into I-Tunes and played it back through the onboard Apple analogue output.
He recorded it back into Logic through the Apogee 16x AD and.......

The polarity was switched!!!!

That means that with Christoph's Logic/Symphony setup the polarity is switched on the way in.

But it also means that the polarity is again switched on the way out!!!!!!

It seems to switch polarity twice.

That means that everything he records will be polarity reversed when being played back on a Pro Tools system.

That might be one of the reasons why a mix played back with Logic/ Symphony can sound different when played back with I-Tunes through the same converters.

I have asked another friend to perform the test with another sound-card and Logic.





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Peter Weihe

arconaut

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #27 on: January 13, 2011, 02:11:24 PM »


Well now my head hurts.

One possibility - not to cast doubt upon Christoph's results - is that his wiring is backwards? If he had pins 2 & 3 mixed up both on input and output, then wouldn't it appear that polarity was correct when feeding the system into itself, yet it was actually flipping the polarity twice? If that were the case, then it could be Logic is fine and Digi Core Audio's input causing the issue.

Otherwise, we now have a few more variables.
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arconaut

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #28 on: January 13, 2011, 02:52:27 PM »

I think the issue is Digi CoreAudio flipping the polarity on input. I just ran a test using Garage Band and had the same thing happen. There are some discussions in various places on the web about the output flipping polarity a few years back, and more recently others have found the same issue on input.


Edited to add:

http://duc.avid.com/showthread.php?t=262613
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Peter Weihe

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #29 on: January 13, 2011, 04:37:10 PM »

arconaut wrote on Thu, 13 January 2011 20:11


Well now my head hurts.

One possibility - not to cast doubt upon Christoph's results - is that his wiring is backwards? If he had pins 2 & 3 mixed up both on input and output, then wouldn't it appear that polarity was correct when feeding the system into itself, yet it was actually flipping the polarity twice? If that were the case, then it could be Logic is fine and Digi Core Audio's input causing the issue.

Otherwise, we now have a few more variables.


Yes, we have to check it again in another studio.
I have already asked another friend to repeat the test with his Logic/Symphony Setup.


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Bob Olhsson

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #30 on: January 14, 2011, 11:56:12 AM »

Bob Ludwig's law:

NEVER turn your back on digital!

I've learned to never trust software developers or manufacturers to get their math right. Test everything...

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #31 on: January 14, 2011, 12:20:43 PM »

Bob Olhsson wrote on Fri, 14 January 2011 08:56

Bob Ludwig's law:

NEVER turn your back on digital!

I've learned to never trust software developers or manufacturers to get their math right. Test everything...
Same is true for analog.  Trust but verify.

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #32 on: January 14, 2011, 12:27:02 PM »

Analog has always been a lot more obvious train wreck.

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #33 on: January 14, 2011, 02:19:29 PM »

Could it be just a graphics problem.  Is the audio actually out of phase?  When you import the audio from the logic capture into Pro Tools, does it look the same, with the first wave form going down?

Steve

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #34 on: January 14, 2011, 05:45:50 PM »

Extreme Mixing wrote on Fri, 14 January 2011 20:19

Could it be just a graphics problem.  Is the audio actually out of phase?  When you import the audio from the logic capture into Pro Tools, does it look the same, with the first wave form going down?

Steve



Yes, it looks the same.
When I import the file of the polarity switched sine wave from Logic into Pro Tools
it is also polarity reversed.

Peter


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Peter Weihe

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #35 on: January 14, 2011, 06:46:37 PM »

Peter,

I had hoped to run some tests today myself but I ran into a major PT problem of my own and the day ran away from me.

Will try and get a look next week.
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Re: Logic with Pro Tools Hardware switches polarity
« Reply #36 on: January 15, 2011, 10:31:14 AM »

KB_S1 wrote on Sat, 15 January 2011 00:46

Peter,

I had hoped to run some tests today myself but I ran into a major PT problem of my own and the day ran away from me.

Will try and get a look next week.



I am sorry to hear that and I hope that you can fix it soon.

Some friends from Berlin will perform some tests with Logic/Motu, Logic/RME and Logic/Pro Tools,M-Box on Monday.

Here is another thread about absolute polarity from 2006.
Some great contributions concerning the practical aspects of switching polarity from our experienced forum members and a discussion about the difference between "polarity" and "phase".

http://recforums.prosoundweb.com/index.php/mv/msg/11037/0/0/ 5361/

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Peter Weihe

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #37 on: January 15, 2011, 10:41:30 AM »

Good news!

My friend Achim just called me.

He has performed the test with his Logic/Symphony setup and the polarity stayed intact.

1. He sent the sine wave out of the Apogee 16x DA and recorded it back through
the Apogee 16x AD and the waveforms looked the same.

2. Then he burned a CD with that sine wave, played it back from an external CD-player
and recorded it with Logic/Symphony through the Apogee 16x AD.

Same result. The polarity stayed intact.

So it doesn't seem to be a problem Logic has with it's own hardware.
It is dependent on the core driver, in our case the Digi Core.

Let's wait what the guys in Berlin will find out with the Motu and RME hardware.
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Re: Logic with Pro Tools Hardware switches polarity
« Reply #38 on: January 18, 2011, 01:13:34 PM »

I applaud Noah for the thorough testing of this issue.  It's vitally important to see the initial polarity rather than rely on cancellation testing on a sinewave signal, as latency might result in 1/2 wavelength delay and lead to the erroneous conclusion that the polarity is inverted.  I would recommend further testing using music as a source for certainty.

In my system the MOTU PCIe-424 and HD192 interfaced show no polarity issues in Logic, though I have not attempted to test this with Protools 9 (don't have it!).

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #39 on: January 18, 2011, 01:31:39 PM »

zmix wrote on Tue, 18 January 2011 19:13

I applaud Noah for the thorough testing of this issue.


Yes, Noah was a great help.
I would like to thank him again for his time.

Quote:

 It's vitally important to see the initial polarity rather than rely on cancellation testing on a sinewave signal, as latency might result in 1/2 wavelength delay and lead to the erroneous conclusion that the polarity is inverted.



That's an important point.
In all of our tests so far we have only observed the initial polarity of the waveform.

Latency was of coarse clearly visible.

Quote:

 
In my system the MOTU PCIe-424 and HD192 interfaced show no polarity issues in Logic, though I have not attempted to test this with Protools 9 (don't have it!).


Thank you,  Chuck for testing it with your system.

That's another hint in the direction that it might either be a problem between Digi Core and Logic or Digi Core only.

We are still waiting for the results from the guys in Berlin.
It will be interesting to see wether the polarity switch also happens with Cubase and
the Digi Core engine.
Also they will try it with Logic and an M-Box.

I have sent both companies, Apple and Logic a report and a link to this thread.
They are working on it and one of the Logic programmers wrote that they plan to get in contact with the guys from Avid about it.



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Peter Weihe

Peter Weihe

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #40 on: February 01, 2011, 08:18:26 AM »

The culprit has shown his face:
It's the Digi Core Audio Engine.

Yesterday one of the Logic engineers sent me a list with the results of his tests with third party software.

Lets first see what we had found out so far:

> We found that the polarity was switched on the AD side only.

> That was the case when the Logic software was running with the Digi Core Engine.

> Pro Tools software with Digi HD hardware did not switch polarity.

> Further tests showed that Logic with Symphony Hardware also did not switch polarity.

So the question was whether the polarity would also be switched when Logic was used with another core driver

or/and whether the polarity would also be switched when another software was used with the Digi Core Driver.

This is the setup, the Logic engineer used for his test.
He played a mono sine wave from a Mac Book Pro with the Symphony Mobile card and a Rosetta 200 interface analog out into the following DAW setups.

The results:

Pro Tools HD Native 8.5 with 192 I/O DAE
Polarity : correct   
                             
Logic Pro 9.1.3 with Symphony 64 / Symphony I/O CoreAudio,
Polarity : correct  

Soundtrack Pro with Symphony 64 / Symphony I/O CoreAudio,
Polarity : correct

Cubase 5.0.1 with Symphony 64 / Symphony I/O ASIO H
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Peter Weihe

Bill Mueller

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Re: Logic with Pro Tools Hardware switches polarity
« Reply #41 on: February 01, 2011, 09:14:30 AM »

Peter Weihe wrote on Tue, 01 February 2011 08:18



Bob Olhsson wrote on Fri, 14 January 2011 17:56

Bob Ludwig's law:

NEVER turn your back on digital!

I've learned to never trust software developers or manufacturers to get their math right. Test everything...


A friend of mine uses Logic with the Pro Tools HD Native hardware for mixing through his SSL console back into the Digi converters. He is also using analog inserts ( Digi 192 Out and In) on some groups before the group goes out to the console.  And now he is constantly counting the converter paths to be sure on which tracks he has to flip polarity and on which an even number of converter paths leads to the correct polarity on the final mix.
 


Peter,

To keep things in perspective here, I would like to point out that on a Neve 8068 console, with transformers and single ended (inverting) amps on every stage from preamp through EQ and various stages of summing, the absolute polarity of the signal changes multiple times.

This does not appear to be much of an issue until you take an insert out on the patch bay pre EQ and find the track inverted on one of a phase related group of mics. We all knew the potential issues and checked polarity with a phase relative track OR used the same pathway on every phase relate track.

Today, on my DM2000 I'm sure there are processing differences between taking an insert out and using it as a direct in to the recorder via Output Patching and the buss assignments on the console. Again, only an issue on phase related tracks, EXCEPT the times I need this feature is when I'm overdubbing a drum kit and need all the tracks to take the same pathway for phase consistency. So when overdubbing in this circumstance, ALL the tracks need to come out inserts, OR I need to use the Input Patching to re-rout the inputs to appropriate channel strips so I can use summing and direct sends on all of them.

I'm just saying, phase consistency will change within many systems due to a variety of conditions and I treat any phase related signal going through any DIFFERENT signal path to be suspect.

Good job!

Best regards,

Bill
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