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Author Topic: V3 (< V3497) digital outputs out of phase relative to analog outputs  (Read 13932 times)

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Offline Brian Skalinder

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FYI, response from Jamie regarding another thread here at TS.  Thought it deserved its own thread:

Hi all-

Jamie from Grace Design here.  I just received an email from Jim, which drew our attention to the thread.  Sorry there has been so much confusion regarding this.

The digital outputs (AES1, AES2, S/PDIF and TOSLINK) are 180 degrees out of phase.  As you know absolute polarity does not have an affect on the sound when the relative polarity between the channels is consistent.  It does however become an issue if you are summing multiple sources that have inverted polarities, which is the case here.  With the V3 digital outputs 180 degrees out of phase from the analog inputs on the 744, the low frequency response will be compromised if these signals are summed.

The fact that the V3's digital outputs are 180 degrees out of phase was only recently discovered when both the analog and digital outs were recorded simultaneously to a workstation.  Upon discovery we immediately corrected this issue in new production units.  Beginning with serial number V3497, all of the digital outputs are in phase with the input.  Any unit prior to this serial number will have inverted polarity on the digital outputs.

Again, when recording two channel audio this is not a problem, but for multichannel or matrix recordings that use the digital outputs, this should be corrected.  Obviously we are here for any of you who want/need to have the digital output in phase with the input and will provide this service at no charge under warranty.  To arrange for this service, please contact me at jamie@gracedesign.com.

Once again our apologies for the confusion and any trouble this may have caused.

Best regards from snowy Boulder, CO

- jamie
« Last Edit: August 31, 2006, 10:17:39 PM by Brian Skalinder »
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Offline Brian

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Re: V3 (< V3497) digital outputs 180º out of phase
« Reply #1 on: March 20, 2006, 04:54:42 PM »
while i don't understand the point of the intial design of the digital output, you have to give it up to grace for top notch support and customer service.

Offline Brian Skalinder

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Re: V3 (< V3497) digital outputs 180º out of phase
« Reply #2 on: March 20, 2006, 05:00:01 PM »
while i don't understand the point of the intial design of the digital output

I don't think the digi-outs 180º out of phase was intentional.
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Offline cleantone

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Re: V3 (< V3497) digital outputs 180º out of phase
« Reply #3 on: March 20, 2006, 05:01:44 PM »
After hearing this I grabbed my V3, plugged in a dynamic to the left channel. Opened a new DP session. Routed the left analog output to MOTU analog 1, track one. Routed AES/EBU 1 (L) to track two. Recorded a peaky click from my mouth. Repeated the same test on AES 2 as well. Low an behold...

I am trying to gather my thoughts. I must have a couple hundred recordings that have the polarity reversed right now. When mixing sources I sometimes flip polarity because it seemingly needs it. I have to deduce the times I haven't I have improperly aligned audio for my mixes. I don't know what to think at this point. Espessially when I've used the V3 for non ambient multitrack recordings. How many recordings of mine are effed up from it? God only knows.

Quote
only recently discovered

How recently and why were we not alerted yet? I would imagine that this website has a very large chunk of the V3 users on it. Is this something that the tech inclined can fix? Obviously rewiring some cables would be a temp workaround. Flipping in the DAW too.
« Last Edit: March 20, 2006, 05:22:50 PM by cleantone »
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Offline Brian Skalinder

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Re: V3 (< V3497) digital outputs 180º out of phase
« Reply #4 on: March 20, 2006, 05:19:12 PM »
if my v3 is not under warranty anymore I have to pay Grace to have them put the digital out in phase with the input?  why should I have to pay for something that I didn't break in the first place?  am I in the wrong here thinking this should not be something we have to pay for?  otoh, I would gladly pay for it if it meant a renewel of my warranty, ala when the optical mod is performed.

thoughts?

Contact Jamie and ask if they'll cover it even if you're out of warranty, given the nature of the problem - a fundamental production flaw on their part.
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Offline cleantone

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Re: V3 (< V3497) digital outputs 180º out of phase
« Reply #5 on: March 20, 2006, 05:25:00 PM »
Quote
So, is this the issue where people say that the V3 adc is thin sounding?

Very well could be. I think I am correct to saw that your speakers are moving opposite of how they should be on playback. That would certainly have an effect on the sound IMO. I'm am not too happy right now.
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Offline Kindguy

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Re: V3 (< V3497) digital outputs 180º out of phase
« Reply #6 on: March 20, 2006, 05:45:40 PM »
Just so I have this right?  Recording 2 mics > recorder like JB3 or Dat the V3 is just fine.

When doing multichannel or matrix recordings is when you'll get inverted polarity on the digital outputs?
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Offline sygdwm

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Re: V3 (< V3497) digital outputs 180º out of phase
« Reply #7 on: March 20, 2006, 05:49:17 PM »
Just so I have this right?  Recording 2 mics > recorder like JB3 or Dat the V3 is just fine.

When doing multichannel or matrix recordings is when you'll get inverted polarity on the digital outputs?


thats how i read it.
mics: (4)akg c460b(a60,mk46,ck1x,ck1,ck2,ck3,ck61,ck63)
pres: oade m148/edirol wmod ua5
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And GODDAMN did I use ALOT of smilies in that post ;D 8) :smoking: :spin:
(P.S.: On a threaded discussion board like this one, there's no need to repeat someone's post when you reply to them; everyone can see all the messages in the thread.)

Offline Brian Skalinder

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Re: V3 (< V3497) digital outputs 180º out of phase
« Reply #8 on: March 20, 2006, 05:56:55 PM »
Just so I have this right?  Recording 2 mics > recorder like JB3 or Dat the V3 is just fine.

When doing multichannel or matrix recordings is when you'll get inverted polarity on the digital outputs?

Depends on whether you think inverting the compression and rarefraction causes an audible difference.  I've inverted my phase on a 2-ch recording before (no mixing) and haven't been able to tell the difference.  But I wouldn't be surprised to hear that others hear a difference.
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Offline cleantone

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Re: V3 (< V3497) digital outputs 180º out of phase
« Reply #9 on: March 20, 2006, 05:58:38 PM »
Quote
Just so I have this right?  Recording 2 mics > recorder like JB3 or Dat the V3 is just fine.
 When doing multichannel or matrix recordings is when you'll get inverted polarity on the digital outputs?

Technically no. When your hearing only the 2 reversed channels it is not as noticable as it would be when mixing multiple sources. The positive and negative voltage information is still backward. Look at the picture I posted. The top is how it should look and the bottom is how it does look.

edit: I knew the minus t's would be coming my way... guess I'll think twice before offering trouble shooting help in the future.
« Last Edit: March 20, 2006, 06:01:27 PM by cleantone »
ISO: your recordings of The Slip, Surprise Me Mr. Davis and The Barr Brothers. pm me please.

Offline Brian Skalinder

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Re: V3 (< V3497) digital outputs 180º out of phase
« Reply #10 on: March 20, 2006, 06:02:22 PM »
edit: I knew the minus t's would be coming my way... guess I'll think twice before offering trouble shooting help in the future.

Please don't let a jackass or two impact your posting - I, for one, appreciate your generally very informative posts.  Keep 'em coming.
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Offline OFOTD

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Re: V3 (< V3497) digital outputs 180º out of phase
« Reply #11 on: March 20, 2006, 06:10:03 PM »
edit: I knew the minus t's would be coming my way... guess I'll think twice before offering trouble shooting help in the future.

+T your way.  I am interested in hearing more. 

If I was mixing two different sources in a matrix what woulld be the effects of this inversion?  Highs not hitting high or lows not thumping low?    Would this muddy up a matrix?


Offline anhisr

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Re: V3 (< V3497) digital outputs 180º out of phase
« Reply #12 on: March 20, 2006, 06:12:41 PM »
+t for the information.  How can you too informed :o
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Offline scb

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Re: V3 (< V3497) digital outputs 180º out of phase
« Reply #13 on: March 20, 2006, 07:17:40 PM »
hmmm

my stereo192 had 1 channel out of phase.  i had mytek correct it so it was in phase with the other channel. but my point of reference was the v3.  i had them correct the out of phase channel so both channels matched the v3's phase

so now i have a v3 and a stereo192 that are both 180 degrees out of phase.  fun

Offline cleantone

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Re: V3 (< V3497) digital outputs 180º out of phase
« Reply #14 on: March 20, 2006, 07:26:44 PM »
Quote
If I was mixing two different sources in a matrix what would be the effects of this inversion?  Highs not hitting high or lows not thumping low?    Would this muddy up a matrix?

That is a really big question. You have to understand a couple of things. First that the real issue at hand here is that the polarity reversal is a big deal. It is true that on playback it is not very noticeable when you flip from + to - on a single source. I'm not sure why that is really. I'd love to find out. I'm not at all a good teacher and also only have a limited grasp of the concepts myself. Maybe there is somewhere online to read up on phase and polarity regarding audio. Here are some basics though. Look at this picture:



Notice the length of the "cycle". It has both "compression" and "rarefaction" in one cycle. Compression is the positive information/pressure, and rarefaction is the negative. This example is a sine wave, a perfect tone. In concert recording your getting what is called a complex waveform. It is combined information from all sorts of frequencies mixed together. That is why it doesn't look smooth like this example. But the positive information and negative information still move upward and downward from the zero volt line. When your taking the digital out of the effected units the positive voltage is being recorded as negative and the negative is being recorded as positive. I'm no "real expert" but I think this is a big deal. I think that this is the information that is "essentially" telling your speaker to move either inward or outward. Compression = outward, rarefaction = inward. So obviously reversing these would seem to be pretty critical. I am not certain about this last part regarding speakers. Can anyone chime in?

The REALLY BIG part of our question is "what would be the effects of this inversion". Especially now that I know my room mics have been reversed in SO MANY instances I don't know how to answer that very well. I have never really been sure if room mics should have their phase flipped or not to begin with. I have heard engineers say that they should. I'd like to be able to have some time to experiment someday with a PA and a room. I think that generating a low frequency onstage (not through the console alone, maybe a synth miced from an amp and run direct) would be the way to go. All I know for sure is that sometimes I've needed to flip polarity and other times not.

To try to answer a bit, the effect would vary. The reason that low frequencies are normally effected morso than higher ones is something to do with the fact that the waveforms are large for low frequencies. The problem is that when you have 2 sources out of phase frequencies are cut and boosted depending. If something is copied, perfectly inverted 180 degrees and recombined without latency the sound will actually disappear. It is the exact positive and the exact negative canceling each other out. Like 2 + negative 2 equals 0, but with sound. It is physics. On top of this when you combine an equal positive with another positive it increases (doubles) the volume. Like 2 + 2 equals 4. With the complex waveforms being combined, even without the polarity issues this happens in degrees. This is why mixing audio is not "simple" (of course it's not rocket science either). Frequencies don't always "play nice" with each other. You will be getting some frequencies cutting while others boost. The large low frequency waveforms tend to be more noticeable because they line up easier to either boost or cut depending on the phase relation. I can't put in in words well. Like I said I'm not a good teacher. If there was a chalkboard I might have a better chance of getting my point across. So if any of this makes sense you can see how having the polarity improper would make the problems that much more apt to occur. Play around with reversing polarity and sliding sources by milliseconds to hear the effects for your self. Lots of plug ins allow you to reverse polarity with a click of the mouse. DP has one called "invert phase". I know some Waves plugs have a little + box that you can change to - . That is flipping the polarity. So if you have a session handy in which your making a matrix try flipping those to hear the effect.

That fact that different frequencies cycle at different rates makes combining sources more difficult.

I'm not sure how coherent this came out. Maybe some of that info will help you understand the effects. Maybe someone can correct or add to what I said. I definitely have trouble putting thoughts to words sometimes. Especially when it is something like this. I have a good understanding but not a complete comprehension good enough to REALLY get my point across.
ISO: your recordings of The Slip, Surprise Me Mr. Davis and The Barr Brothers. pm me please.

 

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