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Author Topic: For those with passive monitor attenuators..  (Read 17406 times)

Viitalahde

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Re: For those with passive monitor attenuators..
« Reply #15 on: July 16, 2009, 03:12:39 pm »

Something just crossed my mind.. The comparison attenuator is clumsy, no way around it.

My converter upgrade is not completely done yet. While processing, I monitor the captured audio through the Lynx Two D/A. While editing, I'm on the HEDD DAC.

The built-in attenuator of the Lavry DA-10 has felt wrong for me since I've always used a passive attenuator, but this feature could be used for exactly this purpose. Previously I was sure I'd get a Blue D/A. Now I need to re-think. But maybe I'll just need to re-evaluate my working methods.

The new console is going to be great. I might post a simplified schematic, if you want.
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Jaakko Viitalähde
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dcollins

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Re: For those with passive monitor attenuators..
« Reply #16 on: July 16, 2009, 03:15:32 pm »

Gold wrote on Thu, 16 July 2009 11:25


That's what I do. I think it works well enough. To my mind it's mostly a Go/No Go test. An exact level match is impossible once more than a tiny amount of processing has been applied.



Same here.


DC

TotalSonic

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Re: For those with passive monitor attenuators..
« Reply #17 on: July 16, 2009, 03:32:40 pm »

dcollins wrote on Thu, 16 July 2009 15:15

Gold wrote on Thu, 16 July 2009 11:25


That's what I do. I think it works well enough. To my mind it's mostly a Go/No Go test. An exact level match is impossible once more than a tiny amount of processing has been applied.



Same here.


DC


After having worked this way about 5 years ago - and since then being able to do "a quick set by ear and it's close enough" level matched a/b's between processed and source paths with a single button push -  
there's no way in heck I'd ever go back to having to turn things up and down.  For me it's an absolute requirement for my studio.

I find it's especially important for me when there's characteristics of the original mix that I really want to make sure I'm preserving even though I'm using some processing to try and effect other elements of the mix - it just lets me do these comparisons free of the "louder is better" bias and while making sure I'm still keeping the integrity of the mix in tact.

Obviously OMMV!!

Best regards,
Steve Berson  

TotalSonic

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Re: For those with passive monitor attenuators..
« Reply #18 on: July 16, 2009, 03:43:32 pm »

Viitalahde wrote on Thu, 16 July 2009 15:12

Something just crossed my mind.. The comparison attenuator is clumsy, no way around it.

My converter upgrade is not completely done yet. While processing, I monitor the captured audio through the Lynx Two D/A. While editing, I'm on the HEDD DAC.

The built-in attenuator of the Lavry DA-10 has felt wrong for me since I've always used a passive attenuator, but this feature could be used for exactly this purpose. Previously I was sure I'd get a Blue D/A. Now I need to re-think.



It's the reason I still hold onto my older Lucid DA9624 as the monitor DAC for my capture DAW's loopback.  It has an onboard attenuator so I can just set the level to where I want it and then this gets fed to one of the inputs of my Coleman M3PHmkII monitor controller (which receives on another one of its inputs a direct feed from the source).  The stereo pot on the attenuator doesn't track perfectly but the differences in the positions varies only very subtly (no more than a 1/4dB - and with a few labelled positions that I've found are perfectly accurate).  I find that the downside's of the older conversion and the less than perfect tracking are more than offset for me being able to do really quick level matched a/b's.

Been meaning to upgrade the Lucid to something like a Lavry DA-11 (whose digitally controlled analog attenuator I believe would track better and would also allow for really accurate recalls) but this has been pushed back in favor of other studio upgrades to date.

Best regards,
Steve Berson

Viitalahde

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Re: For those with passive monitor attenuators..
« Reply #19 on: July 16, 2009, 03:53:54 pm »

This was a quick decision, thanks for the input. I'm omitting the comparison attenuator from the console - another fiddly feature in a console I wanted to simplify in the first place.

I'll either keep on turning them knobs or I'll buy a DA-10. Either way, doesn't affect the console.
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Jaakko Viitalähde
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Andrew Hamilton

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Re: For those with passive monitor attenuators..
« Reply #20 on: July 17, 2009, 12:22:07 am »

I appreciate the theoretical detail of Mr. Putzeys' post.  I have since spoken with another E.E., however, who explained that balanced inputs usually are very sensitive to imbalances in the two signal legs and other parts of the input Z.  So much so, that, for mere audio frequencies, it is often better to go single-ended by tying pin 3 to ground, unless you have serious hum or other noises that can be reduced by signaling "balanced."  According to my contact, the worst problems of unbalanced signaling affect very high frequencies, such as radio and higher.  

In any event, while I have recently tried all possible combinations of wiring that I know of, the RCA jacks on my power amp (still) sound better than the XLR's (no matter what type of source I give the XLR's).  Alas, most of the mastering quality devices with transformerless balanced outputs in my rack do not seem to be  compatible with lifting pin 3 on output - even if pin 3 is grounded on destination through a resistor of the value of the output Z of the driver.   I don't understand exactly why, but some topologies, such as the Lavry MDA824, or Maselec equipment, are just not willing to have the rules bent, as it were, in that particular way.  But, even with unbalanced sources, with pin 3 tied to ground, the Maselec stuff rejects about 120 dB of line noise, according to the manual.  The SpectraFoo noise floor of the whole chain looks practically identical to when I had everything strictly balanced.  

What Mr. Putzeys said, is obviously still sound engineering, in principle.  But, in the field, we have a variety of mutually-exclusive attributes to juggle.  Balanced noise rejection versus twice the hiss on gear that may have fancy(?)  balancing schemes.  Transformer galvanic isolation and euphonic distortion versus absolute polarity and grunge.  Also, as Bob K. pointed out, we want to be able to patch anything to anything, ideally.  But unless we always patch point to point, being careful to use the same output interconnect for the same output (because only it has the correct build-out resistor) and only use compatible gear, then we must embrace the compromise that works/sounds best to us.

Maybe it's a combination of loading issues (caused by slight imbalances in a sensitive circuit) or maybe it's the noise spectrum issue, which Glenn cited.  Or both, plus some other things....  Either way, single-ended signaling is sounding best, here.




Best regards,
   Andrew
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Gold

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Re: For those with passive monitor attenuators..
« Reply #21 on: July 17, 2009, 09:45:38 am »

Andrew Hamilton wrote on Fri, 17 July 2009 00:22

 I have since spoken with another E.E., however, who explained that balanced inputs usually are very sensitive to imbalances in the two signal legs and other parts of the input Z.  So much so, that, for mere audio frequencies, it is often better to go single-ended


I know an unbalanced source impedance degrades CMRR. Degraded CMRR is still better than no CMRR AFAIK. What other problem(s) did your EE say it caused?
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Andrew Hamilton

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Re: For those with passive monitor attenuators..
« Reply #22 on: July 17, 2009, 05:29:58 pm »

Hi Paul, Here's what the guy wrote me (I'll delete his name so that I don't get him in trouble, if'n he's said something incorrect.  Caveat lector.)  


"The important thing with balanced inputs is that the impedance of the two "legs" be as close to equal as possible to maintain the noise-rejection qualities of the balanced input. In the real world, the accuracy of the matching of the inputs is limited by a number of factors, including the accuracy of the two resistors in series with the inputs, and the two other resistors (feedback and non-inverting input-to-ground), as well as the source impedance.

There are many other considerations, depending on what frequency range you are looking at, like stray capacitance and inductance that can have a serious impact on noise rejection at supersonic frequencies, as well.

But for most contemporary equipment, with a balanced input in the range of 10-20kOhms and output impedance much less than 100 Ohms, the "mismatch" caused by connecting the "low" side of the source directly to ground (as versus the driven output) may very well be less significant than the difference in the input impedance due to normal tolerances in the input resistors of the balanced amp. It probably depends on whether the parts are super-high accuracy (like 0.1 percent tolerance) or are hand-selected/hand- adjusted.

...You would still need to keep the connection the same as for "balanced"- using shielded twisted-pair cable. If there is some low-level hum present, the shield can be disconnected at Pin 1 of the balanced input end of the cables if there is a good ground connection between the two pieces of gear other than this shield.

The difference in "source impedance" for the two signal pins (Pin 2 and Pin 3) in this case would be just a bit over that 0.1 percent range for a balanced input impedance of 10k Ohms."






Best regards,
    Andrew



(P.S., How's Tom?)




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Gold

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Re: For those with passive monitor attenuators..
« Reply #23 on: July 17, 2009, 08:16:58 pm »

Andrew Hamilton wrote on Fri, 17 July 2009 17:29


But for most contemporary equipment, with a balanced input in the range of 10-20kOhms and output impedance much less than 100 Ohms, the "mismatch" caused by connecting the "low" side of the source directly to ground (as versus the driven output) may very well be less significant than the difference in the input impedance due to normal tolerances in the input resistors of the balanced amp. It probably depends on whether the parts are super-high accuracy (like 0.1 percent tolerance) or are hand-selected/hand- adjusted.



I can't see how normal 1% resistors found in most pro audio gear would be a worse common mode match than grounding a leg. They would have to be way off. I think you are giving to much weight to the "may very well be" part of the paragraph. The last part of the paragraph is referring to the input circuit. Whether it's good or bad an unbalanced source impedance will cause proportionally good or bad CMRR.
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Paul Gold
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Andrew Hamilton

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Re: For those with passive monitor attenuators..
« Reply #24 on: July 19, 2009, 08:03:25 am »

Gold wrote on Fri, 17 July 2009 20:16

Andrew Hamilton wrote on Fri, 17 July 2009 17:29


But for most contemporary equipment, with a balanced input in the range of 10-20kOhms and output impedance much less than 100 Ohms, the "mismatch" caused by connecting the "low" side of the source directly to ground (as versus the driven output) may very well be less significant than the difference in the input impedance due to normal tolerances in the input resistors of the balanced amp. It probably depends on whether the parts are super-high accuracy (like 0.1 percent tolerance) or are hand-selected/hand- adjusted.



I can't see how normal 1% resistors found in most pro audio gear would be a worse common mode match than grounding a leg.



Well, Sir, he did say that you need 0.1% tolerance in the network to be spot-on... I should think that four [mere] 1.0% tolerance, non-cherry-picked, resistors are indeed capable of ending up way off the mark compared to "...only a little worse than 0.1%..." shouldn't I?  Maybe his 0.1% is too stringent to begin with.  

Regardless, my complaint with the system has never been CMRR, or at least not specifically line noise, itself.  It's a generally brighter sound, when balanced, and possibly a slight "brilliance" is added to the transients.  Is this what happens when CMRR degrades? This sounds more like a loading effect.  Or maybe there's something to the audibility of differential amp hiss, on a psychoacoustic level, at least... Or maybe my balanced input circuit is broken in some other way.  It was bought second-hand as a factory refurbished.  They might have not even tested the XLR's thinking most people would only use the RCA's who bought it second-hand.  My Dunlavy's are second-hand, too (or third!).   They had broken crossovers.  One of them had apparently been improperly assembled at DAL (missing a resistor).  The other had a resistor with a broken leg, rendering it, essentially AWOL from the network. I'm open to even spooky action at a distance as the culprit. (or not);

Can't do this double A/B/X blind.  Only 3rd-eye blind.  

Alas, I can not implement Mr. Putzeys' ideal balanced approach on either my amp or my console, ironically, because the designers of the gear that I happen to have* didn't trust us to know that we could brake the rules responsibly - that we could lift pin 3 on output as long as we remember to shunt (is it?) the inverting leg (say) of the load to ground by the amount of resistance determined by the driving amp's output Z.  And/Or/Instead, they came up with a proprietary scheme (at least one which is not publicly discussed) that allows any dummy (such as I) to use an off the shelf XLR interconnect, and use it to send either a traditionally (fully) balanced or an unbalanced one with excellent noise rejection qualities, either way.  At least this is what it seems like.  

Mr. Putzey's words are "Science" (as Ron Burgundy would put it),  and no one is disputing that.  But there's a locomotive analogy to Science.  Pure Research is the locomotive engine, which is 50 or more years ahead of any likely application.  I'm hopefully somewhere near a dining car, but I realize that it's way in the rear cars of the train.  

This audio mastering has so many debates.  Like, do I want to risk using a pinch roller in order to get rotating lifters?  Or do I want to suffer with stationary lifters and a slow wind and risk servo-snap in order not to have to deal with a pinch roller?  


ITB or signal jack?  Just when the domain converters are getting good, so is dsp (getting good).


Do I want more songs on my iPod at low rez, or do I want them to have better digital resolution, even if there will be forcibly fewer songs, due to the increased demand on storage capacity?

Do I want to go for bottom or for top (end)?  etc... (i.e., 15 or 30 ips).  Choice is nice.  But sometimes there is no satisfaction.  Sometimes, both choices are wrong, and there is no third way.  ):

Spend / Save


I'm just glad he didn't say unbalanced is for turkeys.    I'd have to introduce him to my distinguished e-Mentors on the Blackwood list.  (;



* M•DA-824; MEA-2; MLA-2; MPL-2...   But also, Bob's Trakkers, and possibly other transformerless active balanced stuff?  Just a caveat lector...



Andrew
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Viitalahde

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Re: For those with passive monitor attenuators..
« Reply #25 on: July 19, 2009, 10:12:35 am »

Still thinking of level-matched (or at least a close matched!) comparison between the signals.

I'm monitoring through the DAW, but I quess I could also split the AES/EBU signal from my A/D for a dedicated post-A/D monitoring D/A. A Lundahl splitting transformer and a Lavry DA10 would be pretty ideal. The idea is just to have a more hard-ware method of monitoring than routing a software mixer.

Just going through a period of improving my working methods. Who knows where I'll end. But I like to do it from time to time.
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Jaakko Viitalähde
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Gold

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Re: For those with passive monitor attenuators..
« Reply #26 on: July 19, 2009, 05:25:39 pm »

Viitalahde wrote on Sun, 19 July 2009 10:12

Still thinking of level-matched (or at least a close matched!) comparison between the signals.

I'm monitoring through the DAW, but I quess I could also split the AES/EBU signal from my A/D for a dedicated post-A/D monitoring D/A. A Lundahl splitting transformer and a Lavry DA10 would be pretty ideal. The idea is just to have a more hard-ware method of monitoring than routing a software mixer.

Just going through a period of improving my working methods. Who knows where I'll end. But I like to do it from time to time.


I'm all for easy monitoring of sources. I use four dedicated D/A's and switch with the console. I just don't mind turning the volume knob. That's what it's there for. It's makes it a two hand job instead of a one hand job but I don't mind a little hard work.
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mcsnare

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Re: For those with passive monitor attenuators..
« Reply #27 on: July 20, 2009, 10:15:27 am »

Viitalahde wrote on Sun, 19 July 2009 10:12

Still thinking of level-matched (or at least a close matched!) comparison between the signals.

I'm monitoring through the DAW, but I quess I could also split the AES/EBU signal from my A/D for a dedicated post-A/D monitoring D/A. A Lundahl splitting transformer and a Lavry DA10 would be pretty ideal. The idea is just to have a more hard-ware method of monitoring than routing a software mixer.

Just going through a period of improving my working methods. Who knows where I'll end. But I like to do it from time to time.


I know it sounds stupid, but having a very close level match between source and processed available with just a button made a huge diiference to me. I did the switch + volume knob for a long time and it's just not the same IMO.

Dave

David Glasser

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Re: For those with passive monitor attenuators..
« Reply #28 on: July 20, 2009, 10:42:23 am »

mcsnare wrote on Mon, 20 July 2009 08:15



I know it sounds stupid, but having a very close level match between source and processed available with just a button made a huge diiference to me.




I can't imagine working any other way.
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David Glasser
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lowland

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Re: For those with passive monitor attenuators..
« Reply #29 on: July 20, 2009, 11:14:54 am »

David Glasser wrote on Mon, 20 July 2009 15:42

mcsnare wrote on Mon, 20 July 2009 08:15



I know it sounds stupid, but having a very close level match between source and processed available with just a button made a huge diiference to me.




I can't imagine working any other way.


Me neither. In my case I run synced clips on adjacent streams in the DAW (one feeds the chain, the other is an 'au naturel' monitor) and switch between listening to source or destination with a hotkey. Any level boost in the chain is pulled back to match via the output fader of the TC 6000, my last processor. Once a satisfactory sound is arrived at I correct the level back to just under zero and press record, the monitor clip is then overwitten in real time.
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