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[Bob Olhsson]

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...

[Jay Kadis]

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.

[Bob Olhsson]

Analog has always been a lot more obvious train wreck.

[Extreme Mixing]

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

[Peter Weihe]

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

[KB_S1]

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.

[Peter Weihe]

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/

[Peter Weihe]

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.

[zmix]

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!).

[Peter Weihe]

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.

[Peter Weihe]

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

[Bill Mueller]

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