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Author Topic: V3 (< V3497) digital outputs out of phase relative to analog outputs  (Read 11982 times)

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Offline mmmatt

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Re: V3 (< V3497) digital outputs 180º out of phase
« Reply #30 on: March 21, 2006, 02:18:08 PM »
When worse comes to worse... ask a pro!  Check out the artical I referanced also.


Quote from: mmmatt
>> Hello David,
>> My name is Matthew McCulloch.  I have been researching the effects
>> of phase, or per your article
>> http://emusician.com/mag/emusic_phase/index.html  polarity
>> reversal.  I hope that you can find time to give me a little advice.
>>      I do some pro work, but primarily I am a hobbiest.  I belong
>> to an online forum where we discuss many aspects of hobbiest concert
>> archival
>> recording.  Recently, it was announced by Grace Designs, that their portable
>> pre/ADC the Lunatec V3 has had the coaxial digital output 180deg out
>> of phase
>> (or
>> more accurately with polarity reversed) since the un its
>> inception.  The V3 is
>> a VERY popular tool for us as it is arguably the best portable pre
>> available.
>>     In our little world most people use the V3 is used by some in
>> conjunction
>> with a multitrack rig, and some as simply a 2channel device for ambient
>> recording to either a DAT or to more advanced HD/solid state recorders.
>>      In the case of a multi source situation we all understand that polarity
>> must be flipped to achieve proper phase on the end recording.  There
>> is currently a rather heated debate as to if there is any difference in
>> a 2 channel source.
>>      Here is the question at hand:  With a 2 channel stereo
>> recording made from a unit that is flipping polarity 180 deg from
>> the original
>> source, is
>> there a difference audibly or otherwise.  Secondly, should these recordings
>> be adjusted to be back in correct polarity with the original source?
>>
>> Any help would be great!  Thank you for the information on your site
>> and articles such as the one referenced above.
>>
>> Sincerely,
>> Matthew McCulloch


Quote from: David Moulton
Quoting David Moulton <dave@moultonlabs.com>:

> Dear Matthew,
>
> Thanks for your email.
>
> In my limited opinion, absolute polarity is audible in some circumstances,
> so it should probably be accounted for, as part of good recording craft.  At
> the same time, its audibility effect seems to me to be quite minor, and it¹s
> no sure bet the ³correct² polarity is going to sound ³better² than incorrect
> polarity in any given case.
>
> So, mostly, once I¹m satisfied that relative polarity is correct in each
> source case, I don¹t worry about it unless I notice something really odd.
>
> I hope this helps.
>
>
> Best regards,
>
>
> Dave Moulton


>          Moulton Laboratories/Digital Media Services
>                978-448-6828, www.moultonlabs.com
>                           I mixed and mastered
>   the Hybrid SACD ³From Exile to Exaltation² which won the
>     2005 Independent Music Award for Best Gospel Song
>                  and has been listed among
>     ³Best of the Year Discs² by Audiophile Audition
>     I¹m the author and producer of the Audio Education Hits
> "Total Recording," "Golden Ears" and "Dave's Audio Lectures"
>      Copyright 2006 by David Moulton.  All rights reserved.
>                      Nunc tutus exitus computaris

Quote from: mmmatt
It helps a lot David.  Thanks for your time.

Matt

So what this means, is it is subjective.  It is most certainly not absolute as was explained to me years ago.  I'm gonna have to look that guy up.  Anyone know a Scott Swire?  Please all accept my appologies, and thanks to Freelunch for calling me on it...   
     I would also like to point out the potentially TRUE golden ears of TS being Brian Sax.  He has always bitched about the ADC of the V3 being thin and it seems as though there could now be reason for this!

Matt
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Offline Brian

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Re: V3 (< V3497) digital outputs 180º out of phase
« Reply #31 on: March 21, 2006, 02:30:41 PM »
awww shucks.....don't give me that much credit ;)   lots of others have shared my feelings before i owned that unit.  Anybody remember Natelsky's posts? ;D But +Thanks for the compliment!

However I didn't own the V3 for too long because of the A>D.  It seemed like everything 200Hz and lower really suffered to my ears.  I switched back to V2 > M1 because i thought it sounded a lot fuller and better in the low end.  I was also running TL's at the time so i was surprised at just how much their low end suffered through the V3.  All of my TL>V2>modsbm1 and TL>V2>M1 recordings are much better sounding than my TL>V3 recordings.

After reading this thread.....especially Clinton's posts.....i'm still confused on how Grace could not have noticed this in initial development and production. At least they are willing to fix it.

Offline cleantone

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Re: V3 (< V3497) digital outputs 180º out of phase
« Reply #32 on: March 21, 2006, 02:41:55 PM »
Good work Matt. What he said makes absolute sense.

Quote
I would also like to point out the potentially TRUE golden ears of TS being Brian Sax.

Me too. I am really disapointed in myself for not ever noticing it. I can say that after flipping the polarity of one of my recent recordings. I was able to match the timing in seconds where it would normally take a while. After matching a snare hit I would nudge by a matter of samples over and over until I found the lesser of the evils. I think from now on I'll be matching kick drums and low frequency sounds since they are what can be effected most easily. It is still a bit of a chore. The distance of different sound sources combined with the different cycle rates combined with the effects of comb filtering make it a bugger. Unless a band is onstage making sine waves you can't match frequencies across the spectrum 100%. There is too much information in the complex waveform for that to happen. That is why I was able to make "good" mixes with the polarity flipped on the audience recording. In cases in which I couldn't I certainly have flipped phase. I just had no idea it was because of a flaw in the unit. Always assumed it was sound anomolies. I did so much auditioning and phase flipping this morning I can't even mix today. I'm resting my ears for at least a full day. So I'm having a Curb Your Enthusiasm marathon. Plus there is a Twilight Zone one on TV. My ears are shot right now.

I'm still dumbfounded. I'm also waiting to hear back from Jamie about getting it fixed. From looking at the numbers can we assume that there has only been about 500 units made? If so that is a little surprising. Though I guess it shouldn't be.

Quote
However I didn't own the V3 for too long because of the A>D.  It seemed like everything 200Hz and lower really suffered to my ears.  I switched back to V2 > M1 because i thought it sounded a lot fuller and better in the low end.  I was also running TL's at the time so i was surprised at just how much their low end suffered through the V3.  All of my TL>V2>modsbm1 and TL>V2>M1 recordings are much better sounding than my TL>V3 recordings.

I have always assumed my non perfect monitoring situation had a lot to do with my low end issues when I felt I had them. I wonder how many hours I have tossed away reworking mixes and listing on all sorts of playback systems? Far too many to think about. I am soldering up some shorty polarity reversed Canare's for a quick fix. I'd rather do that than process the files after the fact. Now I wish I had one of those "burn in" units to use. Maybe I should just snip some old cables to save that effort. Eureka!

Quote
After reading this thread.....especially Clinton's posts.....i'm still confused on how Grace could not have noticed this in initial development and production. At least they are willing to fix it.

Seriously. I really don't know how that could have went three years without being discovered. Also, again how it was not announced either. Pretty crazy.  ::)
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Offline it-goes-to-eleven

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Re: V3 (< V3497) digital outputs 180º out of phase
« Reply #33 on: March 21, 2006, 03:16:23 PM »
Thanks for getting another source on the phase question, Matt.

I called Grace today to try and figure out whether my v3 has the problem (it is in a rack and I can't get to the serial number).  I bought mine around Dec 9 and it is apparently one of the first 10 units to ship with the fix.  I'll verify that soon enough just to be sure.

But FWIW.. I did a comp a while back with this v3 and it seemed to be lacking bass. I think there were too many differences in this comp to infer too much from that but I thought I'd mention it. Especially since Alex had a great quote "Must be the V3 that sucked the low end out of the Rmod box."

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Offline Brian

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Re: V3 (< V3497) digital outputs 180º out of phase
« Reply #34 on: March 21, 2006, 03:17:39 PM »
clinton - what you said is the exact reason why i don't track drums unless each preamp for each mike has a polarity switch.  i find myself routinely flipping polarity on the kick drum or one of the overheads in order to maintain that "Full" sound and non-weird sounding midrange affected by a comb filter.  in my short experience out of phase audio yields a suffered low end a weird sounding mid range.

don't beat yourself up though.  

Offline Brian Skalinder

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Re: V3 (< V3497) digital outputs 180º out of phase
« Reply #35 on: March 21, 2006, 03:30:28 PM »
in my short experience out of phase audio yields a suffered low end a weird sounding mid range.

But in this scenario, as I understand it, out of phase relative to the other audio involved in recording/playback is fundamentally different than inverted but relative phase.  Not sure I understand the parallel you're drawing...?

I really don't know how that could have went three years without being discovered.

I think it took 3 years to identify precisely because it is not audible (at least not to me).  When Grace first reported that the first 100 V3's did not have a DC offset of 0, some people completely freaked out.  One of the explicitly stated reasons by Mike Grace that they didn't catch it is because the DC offset simply wasn't audible.  (Still, of course, they offered to fix all the boxes affected under warranty.)

Anyway...I've been thinking about phase within the context of 2 channel recording, and my initial thoughts suggest that it doesn't (or shouldn't) matter, that what's important is relative phase across the two channels - and that's why I don't hear a difference when ABX-ing a 2-ch recording with a particular phase v. inverted phase.  Lemme test my thoughts on everyone...

We have a speaker.  A + voltage pushes the cone outwards, a - voltage pulls the cone inwards.  The result, in a perfect world, is a single-cycle sine wave of given amplitude.  In reality, the waveform propagates in all three dimensions and is much more complex, but for the sake of simplicity in discussion, let's look at this sine wave in two dimensions.  For this two dimensional waveform, relative to the horizontal plane on which my speaker rests the + side of the sine wave arcs upwards and the - side of the sine wave arcs downwards.  At some defined point, X, from the speaker, the waveform reaches my ears.  Let's assume that at this point, the + arc reaches my ears first, followed by the - arc.  Make sense?

Now, two modifications to the above scenario:

<01>  Change my listening orientation at point X
For example, hanging upside down with my head in precisely the same location, X, as above.  Now, the waveform reaching my ears is effectively inverted relative to to the previous scenario.  The + arc still reaches my ears first, followed by the - arc, but the orientation of the waveform relative to my ears is 180º inverted.  Does this fundamentally change the way I hear the waveform?  Since our listening position is never precisely the same across any period of listening time (unless you're strapped to a body board, with a neck brace, restricting all movement), our listening orientation impacts the phase throughout our listening experience.

<02>  Change my listening position from point X to point Y
Let's assume point Y is forward of my current listening position by exactly 1/2 of the waveform cycle.  The result is that now the - arc of the waveform reaches my ears first, followed by the + arc.  In the more complex real world, different frequencies will reach our ears with different phase - some frequencies' - arc will reach our ears first, other frequencies' + arc will reach our ears first, and still others somewhere in between.  So does this phase offset fundamentally change the way I hear the waveform?  Maybe in the most absolutely controlled of playback environments, but even for most very high end playback systems I don't see how phase inversion would matter to the listener.

It seems to me that if we extrapolate this very two dimensional model into three dimensional reality, phase inversion will occur as a result of either or both of the above scenarios, and that the phase inversion (and time arrival offset, for that matter) makes no difference, or at least is no more or less important than one's ears' orientation (in all three dimensions) relative to the speaker.

Thoughts?
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Offline Brian

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Re: V3 (< V3497) digital outputs 180º out of phase
« Reply #36 on: March 21, 2006, 03:32:07 PM »
i'm not drawing any parallels.  just making a statement based upon my observations.

Offline Brian Skalinder

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Re: V3 (< V3497) digital outputs 180º out of phase
« Reply #37 on: March 21, 2006, 03:34:40 PM »
i'm not drawing any parallels.

Heh, well...no wonder I didn't grasp one, you weren't making one!  I get it now.  Thanks for the clarification, Brian.
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Re: V3 (< V3497) digital outputs 180º out of phase
« Reply #38 on: March 21, 2006, 03:54:44 PM »
BTW - i'm looking into your post. I'm trying to find info on why correcting DC offset is important and not really related to the sound of your audio.  something about sending a master to a pressing house with DC offset will yield "errors" but i can't think of them off the top of my head.

The pros at prosoundweb.com have talked about this extensively but searching that forum is like 6x the battle of finding info here.

<01>  Change my listening orientation at point X
For example, hanging upside down with my head in precisely the same location, X, as above.  Now, the waveform reaching my ears is effectively inverted relative to to the previous scenario.  The + arc still reaches my ears first, followed by the - arc, but the orientation of the waveform relative to my ears is 180º inverted.  Does this fundamentally change the way I hear the waveform?  Since our listening position is never precisely the same across any period of listening time (unless you're strapped to a body board, with a neck brace, restricting all movement), our listening orientation impacts the phase throughout our listening experience.

<02>  Change my listening position from point X to point Y
Let's assume point Y is forward of my current listening position by exactly 1/2 of the waveform cycle.  The result is that now the - arc of the waveform reaches my ears first, followed by the + arc.  In the more complex real world, different frequencies will reach our ears with different phase - some frequencies' - arc will reach our ears first, other frequencies' + arc will reach our ears first, and still others somewhere in between.  So does this phase offset fundamentally change the way I hear the waveform?  Maybe in the most absolutely controlled of playback environments, but even for most very high end playback systems I don't see how phase inversion would matter to the listener.

It seems to me that if we extrapolate this very two dimensional model into three dimensional reality, phase inversion will occur as a result of either or both of the above scenarios, and that the phase inversion (and time arrival offset, for that matter) makes no difference, or at least is no more or less important than one's ears' orientation (in all three dimensions) relative to the speaker.

Thoughts?

wow....where to start....

first off...i'm confused by this supposed "2D model".  there;s nothing two dimensional about how we perceive audio.  I'm also confused on why you think that changing your head position will correct/flip phase.  we hear 3 dimensionally and we percieve direction based upon time of arrival and amplitude.  hanging upside down won't be any different than sitting up in a chair at the same location.  you ears should(at least in theory in my mind) should pick up the sound the same.

in your second scenario, you are percieving half or quarter waves depending on which frequncy you are using in your test.  you are getting pretty scientific thus you need to figure out how long the wave is you are using.  wavelength = speed of sound divided by the frequency in Hz.  you can't just think that because you are exactly half way then the negative arc will reach your ears first.  you have to properly measure that.

or are you assuming that in your second scenario?

Offline mbgrace

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Re: V3 (< V3497) digital outputs 180º out of phase
« Reply #39 on: March 21, 2006, 03:59:01 PM »
Hi All,
First, let me apologize for our mistake in wiring the a/d converter in the V3.  It is a simple thing to check in the design phase of a product and we missed it.
If you are a V3 owner and would like to have your unit corrected please send it to us and we will quickly make the repair, test, calibrate, burn-in and return your unit to you.  There is no need to contact us ahead of time as we have posted a Return Authorization form on our web site at: http://www.gracedesign.com/support/v3_polarity_rma.pdf   Simply fill in this form and put it in the box with your V3 and ship it to us. 
While all V3s are currently under the original 5 year factory warranty we will repair this problem under warranty for the lifetime of the unit.

Now,  I think I should comment on the effects of this problem with respect to stereo and multitrack recording.  The fact that we missed this problem in all of our R&D listening tests and that we shipped almost 500 units without this problem being detected is a testament to how subtle absolute phase reversal is.  In fact, it was initially brought to our attention by a customer who happened across the problem while viewing waveforms on the computer screen.  While I personally have difficulty hearing the difference of polarity reversal, I do know people who claim that it is audible.  When pressed, however, they have not been able to give a description of the difference or weather it is “worse” or “better” sounding. 
That said, I fully agree with David Moulton's opinion that polarity of every signal involved in a recording should be “accounted for”.  As tapers and engineers we need to rely on our tools to behave in a predictable way and this includes polarity.
This becomes much more important in the context of multi channel recording as the audible effects of absolute polarity reversal when mixing with correctly phased signals is not subtle.  In the case of a soundboard matrix recording, if the room mics are inverted relative the the soundboard signal, there will be some cancellation when the two are mixed together.  The reason that some of you have reported difficulty with track alignment is undoubtedly because of this.  I sincerely apologize for any recordings that were rendered badly because of this issue.

Again, my apologies for the confusion here.  We are doing all that we can, as quickly as we can, to rectify this problem.
As always, our mission is to provide the best possible tools and support for capturing and creating the art of music.
Sincerely,
Michael Grace
Michael Grace
Grace Design/Lunatec LLC

Offline Brian

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Re: V3 (< V3497) digital outputs 180º out of phase
« Reply #40 on: March 21, 2006, 04:07:07 PM »
Thanks for the response Mike.  Does this mean that Grace design does not put a tone from an oscillator through each unit and look at it through a scope of some sort or a frequency analyzer on a computer prior to authorization for shipping?  It seems to me that the problem could have been seen then ???

i know your time is limited but if you could go into more detail on how you test your products that would help.

edit:  or maybe this test does not show the problem?  Just curious.
« Last Edit: March 21, 2006, 04:08:41 PM by Brian Sax »

Offline mmmatt

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Re: V3 (< V3497) digital outputs 180º out of phase
« Reply #41 on: March 21, 2006, 04:13:27 PM »
Hi All,
First, let me apologize for our mistake in wiring the a/d converter in the V3.  It is a simple thing to check in the design phase of a product and we missed it.
If you are a V3 owner and would like to have your unit corrected please send it to us and we will quickly make the repair, test, calibrate, burn-in and return your unit to you.  There is no need to contact us ahead of time as we have posted a Return Authorization form on our web site at: http://www.gracedesign.com/support/v3_polarity_rma.pdf   Simply fill in this form and put it in the box with your V3 and ship it to us. 
While all V3s are currently under the original 5 year factory warranty we will repair this problem under warranty for the lifetime of the unit.

Now,  I think I should comment on the effects of this problem with respect to stereo and multitrack recording.  The fact that we missed this problem in all of our R&D listening tests and that we shipped almost 500 units without this problem being detected is a testament to how subtle absolute phase reversal is.  In fact, it was initially brought to our attention by a customer who happened across the problem while viewing waveforms on the computer screen.  While I personally have difficulty hearing the difference of polarity reversal, I do know people who claim that it is audible.  When pressed, however, they have not been able to give a description of the difference or weather it is “worse” or “better” sounding. 
That said, I fully agree with David Moulton's opinion that polarity of every signal involved in a recording should be “accounted for”.  As tapers and engineers we need to rely on our tools to behave in a predictable way and this includes polarity.
This becomes much more important in the context of multi channel recording as the audible effects of absolute polarity reversal when mixing with correctly phased signals is not subtle.  In the case of a soundboard matrix recording, if the room mics are inverted relative the the soundboard signal, there will be some cancellation when the two are mixed together.  The reason that some of you have reported difficulty with track alignment is undoubtedly because of this.  I sincerely apologize for any recordings that were rendered badly because of this issue.

Again, my apologies for the confusion here.  We are doing all that we can, as quickly as we can, to rectify this problem.
As always, our mission is to provide the best possible tools and support for capturing and creating the art of music.
Sincerely,
Michael Grace

That's what you call customer service folks... Thanks for your attention on this Mike!!!!!



first off...i'm confused by this supposed "2D model".  there;s nothing two dimensional about how we perceive audio.  I'm also confused on why you think that changing your head position will correct/flip phase.  we hear 3 dimensionally and we percieve direction based upon time of arrival and amplitude.  hanging upside down won't be any different than sitting up in a chair at the same location.  you ears should(at least in theory in my mind) should pick up the sound the same.


alright Mr. Golden Ears... ha!  True phase is actually relative to delay.  Actual phase reversal is diferent accross the audio spectrum because each wave length is difference in size.  At a point 1/2 way through the wave length, the phase is inverted 180 deg.  What we have with the v3 is actually not phase but it is polarity reversal.  so the distance from one source to the other does have impact on absolute phase (I think that is linear phase).  So unless you are perfectly positioned between your two speakers.  You are infact hearing something that is out of phase by a tiny bit.  Even by compensating with louder volume on the side furthest away, you are still not correcting phase because the amplitude does not determine the size of the wav.
   So, you are only correct if your ears are perfectly equidistant from each of the two sources.

Matt
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Offline Brian Skalinder

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Re: V3 (< V3497) digital outputs 180º out of phase
« Reply #42 on: March 21, 2006, 04:15:17 PM »
I'm trying to find info on why correcting DC offset is important and not really related to the sound of your audio.  something about sending a master to a pressing house with DC offset will yield "errors" but i can't think of them off the top of my head.

I vaguely recall reading a piece off-TS that discussed sonic impact of DC offset during the mastering process.  Don't think I'll go try to find it again, though. 

first off...i'm confused by this supposed "2D model".  there;s nothing two dimensional about how we perceive audio.

Yes, I understand we perceive audio three dimensionally.  The two dimensional model was for simplicity of discussion and it seems easy enough to extrapolate that model out into the more complex three dimensional world.

I'm also confused on why you think that changing your head position will correct/flip phase.  we hear 3 dimensionally and we percieve direction based upon time of arrival and amplitude.  hanging upside down won't be any different than sitting up in a chair at the same location.  you ears should(at least in theory in my mind) should pick up the sound the same.

That's kinda what I was getting at in a roundabout sort of way.  Again, using the two dimensional model for discussion simplicity, it shouldn't matter sonically to the listener whether the "upward" arc is generated by a + voltage driving the speaker outwards or a - voltage driving the speaker inwards.  Extrapolate into the more complex three dimensional world, and whether any given waveform's arc is produced by a + voltage driving the speaker outwards, or a - voltage pulling the speaker inwards simply doesn't matter.  Why would it matter if any given waveform's arc is up or down, left or right, or anywhere in between - I don't see how it could matter.  Hanging upside down was simply a way of illustrating inversion in the two dimensional model without changing the polarity of the source (in this case recording + playback system).

in your second scenario, you are percieving half or quarter waves depending on which frequncy you are using in your test.  you are getting pretty scientific thus you need to figure out how long the wave is you are using.  wavelength = speed of sound divided by the frequency in Hz.  you can't just think that because you are exactly half way then the negative arc will reach your ears first.  you have to properly measure that.

or are you assuming that in your second scenario?

I wasn't assuming any measurement.  The specific measurement doesn't matter, it's the abstraction in this case that matters.  Pick whatever measurement you want, such that the single two dimensional waveform in my example reaches your ears - arc first, followed by + arc, i.e. opposite order of the original scenario.

Of course, in the complex real world - as I suggested - given a broad range of waveform cycle lengths, no single location will cause all frequencies to arrive + arc first followed by - arc.  Some will arrive - arc first, then +.  And still others will arrive at some other interval mid-arc.  Which is exactly my point - phase inversion - whether the speaker pushes out or pulls in to generate the waveforms arc - as long as its relative across channels - not only shouldn't matter theoretically to the listener, but shouldn't matter practically because there's FAR more going on in the real, complex listening world that impacts the listening experience.

But I'm no techie, I'm just trying to think through this stuff for myself based on my own very limited knowledge set.  For all I know, the phase inversion makes a world of difference - but it's not audible to my ears.
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Offline Brian

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Re: V3 (< V3497) digital outputs 180º out of phase
« Reply #43 on: March 21, 2006, 04:16:38 PM »
i'm sorry....i should have said polarity reversal.  sorry for the confusion!  biggest word swap in audio history? when a company who makes pre's says that they have phase inverter switchs....i get a little worried about their product ;)

Offline Brian

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Re: V3 (< V3497) digital outputs 180º out of phase
« Reply #44 on: March 21, 2006, 04:18:10 PM »
re: skalinder's last post......

as an engineer once told me. 

waveforms mean nothing.  perception is everything

 

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