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Fusion analog inputs unusual behavior


gabi
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Hi Gabi,

But isn't it all about the noise level?  The point of good mic preamps is to get the highest dynamic range with the lowest noise floor.  I for one ride my trims all the time to adjust for variations in the different mics  and performances (though often the trims are in the wireless transmitter, but that's another story).  You should be able to set the trims by ear with much better accuracy than by a random point on a pot scale.  That is why the Nagra recorders had a headphone volume control that had to be adjusted with a screw driver.  The point was to set a comfortable level so the only variable was adjustment of the mic gain. 

btw, I re-checked the Deva meter screen you posted and the gain difference between channels 4 and 5 was closer to 5 db, not 10 (-12 to -17).  The Deva/Fusion mic pres and recording system have such wide dynamic range that minor differences are inconsequential.  I don't think there is anything wrong with your Fusion.  I'd be wary about trying to adjust the photo cell circuitry.  If it was something that was feasible to do I'm sure Zaxcom would have already done it.

Billy

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I'd like to quickly chime in to say that even though I do not use the Zaxcom recorders, it would seem that Billy's logic is reasonable.

As long as your gain structure is not compromised (increased noise floor or unpleasant compression), it doesn't really matter how the input gain is set on the recorder.  Make your gain adjustments on the mixer for optimal sound at the correct levels.  The couple of dB here or there difference on the recorder's input gain seems to me to be an acceptable compromise if the inputs are as quiet as people say.

Robert

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In multi-channel recordings it is essential that all mics are set with the same gain. with a deva you would have to calibrate each input every time you switch from line to a multi-channel mic.

what if you go from a quiet room tone to heavy street noise? How do you set your generator?Each mic has a different sinsitivity. There is no 0dB output on a mic. This whole procedure is rediculous in practice. For 4 individual lavs it might not matter that much but for stereo and 5.1 recordings it is crutial to have mic pres that give you what they indicate.

I do not have a single other device in my studio or around my field equipment that I need to calibrate with a tone to work around a very coearse factory allignment.

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I'd like to quickly chime in to say that even though I do not use the Zaxcom recorders, it would seem that Billy's logic is reasonable.

As long as your gain structure is not compromised (increased noise floor or unpleasant compression), it doesn't really matter how the input gain is set on the recorder.  Make your gain adjustments on the mixer for optimal sound at the correct levels.  The couple of dB here or there difference on the recorder's input gain seems to me to be an acceptable compromise if the inputs are as quiet as people say.

Robert

Billy's logic is good for Zaxcom, for me, not!

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lol, Billy's logic is good for Billy too!  I've been using Deva's for ten years now and never have to worry about overload or excessive noise. 

And to respond to Peter, I (and many field mixers) quickly set trims by ear.  The only time I use tone is when I use radio mics.  Since the mic pre is in the transmitter (and set by ear, largely because every lav or plant mic has a wildly different output level) I want to confirm that the output levels of all the radios are the same so I generate -20 out of the receivers.  Each trim pot is in a slightly different position but that has never been a problem of concern to me.  It would be the same if I did a live 5.1 recording.  I'd set the trims by ear.  The audio gain into each mic would be different so I'd only be concerned that the background noise level was the same so there would be no pumping between tracks. 

Anyway, to each their own.  Gabi, before going into your machine, give Glenn at Zaxcom a call.  He'll advise what is possible or not.

All the best for the holidays!

Billy

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Bily, I envy your hearing capabilities being able to level match a 5.1 rig by ear with headphones!

Anyway. Generally I think it´s just not right for a professional machine of this class to have the inputs this far apart. In professional grade audio equipment I have not seen this yet. Heck, we spend lots of money to buy matched pairs of microphones  and then plug them into a machine where every input gives us +-10dB of level being set at identical gain trim?

Not acceptable at this price tag, sorry.

I bet you would send your pair of Schoeps back to the factory if they came with such a high output difference first thing in the morning. But then you might not even notice because there´s no way to find out. Could be the mics OR the inputs not matching ;-)

I just sent a lectro SR receiver off for repair because the two outputs where off by 8dB being set at identical levels. Now I find out that it could as well be the Deva´s inputs being "within specs" of +-3dB. How am I ever going to ID malfunctioning mics or other connected devices when my primary recorder does not give me confidence in what I set is what I get?

Not fun.

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To Peter and Gabi, I really think this is a non issue in the real world. Let me try and clarify:

"Anyway. Generally I think it´s just not right for a professional machine of this class to have the inputs this far apart. In professional grade audio equipment I have not seen this yet. Heck, we spend lots of money to buy matched pairs of microphones  and then plug them into a machine where every input gives us +-10dB of level being set at identical gain trim?

Not acceptable at this price tag, sorry"

Possibly not acceptable to you but obviously totally acceptable to the hundreds of satisfied sound mixers using the Deva everyday and not having any of the problems you discuss. For me personally with over 12 years using the Deva on over 20 feature films, I have never ever had a problem with input gain setting. As Glenn Sanders has explained, the analog circuit, input to input, will never be exactly the same. In the old days where ALL our levels and trim settings were analog, we relied on looking at the trim pot knob and remembering that it should be set at "around 2 o'clock" when using the Schoeps microphone. For normal dialog recording this would always sound right. If it was too loud, we would turn it down, if it was too low, we'd turn it up. There was never a numeric value available unless we measured voltage at the output (not something that any of us would ever do in the field). Following this procedure for input gain trim for the last 40 years of my career seems to have worked out just fine. I had no problem utilizing the same procedures as we moved into the digital arena.

"I bet you would send your pair of Schoeps back to the factory if they came with such a high output difference first thing in the morning."

This is a poor example. The only numeric value for the output sensitivity for the microphone is on the specification document for the microphone and is stated as + or - 5db. You will never know if YOUR mic is within this spec unless you put it on the test bench and measure output voltage. Because the microphone is an analog device, this output level also CHANGES throughout the day and of course can also change with age throughout the life of the microphone. This is one of the reasons why we have INPUT trims in the first place. I will add that if I were to hear that Schoeps mic no. 1 consistently seemed a lot lower in level when plugged into my input (set at the normal 2 o'clock position I mentioned earlier), I would check the microphone and possibly send it back --- this is NOT the same issue as input gain trim difference.

"I just sent a lectro SR receiver off for repair because the two outputs where off by 8dB being set at identical levels. Now I find out that it could as well be the Deva´s inputs being "within specs" of +-3dB. How am I ever going to ID malfunctioning mics or other connected devices when my primary recorder does not give me confidence in what I set is what I get?"

If you feel that you do need numeric value while troubleshooting something, just do what Billy S. recommends which is to use a tone generator, set the trims on the Deva inputs, then plug in the device that is suspect --- better yet, use the SAME input and substitute each device where you have doubt that their output levels are correct (this is the substitution procedure I would use while trying to "ID malfunctioning mics or other connected devices").

Maybe I just don't get it why this input trim thing is a problem for you Peter. For Gabi, who originally brought this to our attention, I suggested that a call to Zaxcom would be the best idea. I don't know if that call has been made or not.

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Jeff,

I could write a big paragraph for each of your points, can we at least agree on the fact that if you have an 8-channel mic pre and you set every channel to the same amplification and what you get on your outputs on each individual output randomly differs by almost 10dB or even 6dB according to zaxcom specs it seems like there's something wrong?

Just because only a few users have noticed this or don't care because they never record with matched mics in complex setups doesn't mean this is what you can expect from a professional device.

I think they need to introduce another trim page for the trim page so we can conpensate for this.

It feels a bit weird to set my levels almost 10dB louder on one channel when I have a matched pair of mics that are matched within +-1dB with eachother.

I find this rather irritating.

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On every desk I've ever used, tone in on a channel routed to the stereo bus would hit 0 with all channel trims in roughly the same position.  Our 56 channel XL4 worked like this, and so does my 4 channel 442.  Thus I've always assumed that's how the front end of these products are designed, and I can see, from my perspective anyways, how it would cause concern.

Maybe with digital it's different somehow.

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I could write a big paragraph for each of your points, can we at least agree on the fact that if you have an 8-channel mic pre and you set every channel to the same amplification and what you get on your outputs on each individual output randomly differs by almost 10dB or even 6dB according to zaxcom specs it seems like there's something wrong?

--- snip ---

It feels a bit weird to set my levels almost 10dB louder on one channel when I have a matched pair of mics that are matched within +-1dB with eachother.

I find this rather irritating.

Has this been your experience with your Deva, that you have used matched microphones and have had to set gain trims 10db apart? If so, this has obviously been more than just irritating for you. I am still puzzled why no one else, other than Gabriela and you, have encountered this. From my brief discussion with Zaxcom, 10db difference is greater than would be expected, so I imagine it is possible that your Deva and Gabi's may require some attention from Zaxcom.

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" I think it´s just not right for a professional machine of this class to have the inputs this far apart. "

that's why there are trim controls!

" essential that all mics are set with the same gain. "

when that precision is needed, a precision signal generator needs to be used to align all the trims, individually; of course the mic, or even line, outputs into the channels may not be precisely matched...

Billy, JW, and others understand this!

what Gabi, Gabriel and Peter are seeing is a finer look at the slight differences than they have seen before.  much finer than the slight differences in witness mark alignment!

" with all channel trims in roughly the same position. "

exactly

" level being set at identical gain trim? "

identical, or roughly the same ??

"another page on the menu to calibrate the inputs"

ah, a pre-trim trim!

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" with all channel trims in roughly the same position. "

exactly

I'm talking within a few degrees of each other.

Not enough of a difference to be seen when visually scanning across the channels.

The point being, preamp gain structure was pretty much identical across the board.

Certainly no more than .5dB either way.

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I'm talking within a few degrees of each other.

Not enough of a difference to be seen when visually scanning across the channels.

The point being, preamp gain structure was pretty much identical across the board.

Certainly no more than .5dB either way.

Since 1967 with sound, I never saw a difference greater than 0.5dB.

Gabriel

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pretty much identical across the board. "

Ah, then you have not measured exactly, or cross calibrated exactly, and a few degrees could be a pretty good difference...

" I never saw a difference greater than 0.5dB. "

have you been measuring that??  just putting the knobs on the pot shafts could iinclude a couple dB difference...

you never saw it, because you never had as good a picture of it as you do now on the screen.

now, of course, it is possible that your units are out of tolerance, and thus need servicing.

or maybe the trim just needs to be trimmed!  that is what it is for!

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Billy, JW, and others understand this!

what Gabi, Gabriel and Peter are seeing is a finer look at the slight differences than they have seen before.  much finer than the slight differences in witness mark alignment!

6dB (zaxcom allignment specs) to 10dB (reported from users) you call "slight" differences? From my Millennia preamps to my 744 to my 788 even my PD4 I have never seen such differences between channels at a given gain setting.

Jeff, what about your cooper mixer? Did you ever set the channel gain on a stereo-mic differently by THAT much for each mic to get a balanced stereo image? I highly doubt it.

Anyway, it´s almost christmas and time for other things....

Have a great christmas you all!

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pretty much identical across the board. "

Ah, then you have not measured exactly, or cross calibrated exactly, and a few degrees could be a pretty good difference...

Ah, Excuse me for not being thoroughly scientific in my statements.

I did measure exactly with an analyzer.  It was part of our maintenance schedule.

" I never saw a difference greater than 0.5dB. "

have you been measuring that?? 

See above.

you never saw it, because you never had as good a picture of it as you do now on the screen.

now, of course, it is possible that your units are out of tolerance, and thus need servicing.

or maybe the trim just needs to be trimmed!  that is what it is for!

What screen? I don't own a Deva. 

I'm just relating my experience with gain structure in console preamps.

Maybe it's helpful to the OP, maybe not.

It's just part of that whole 'sharing of resources' idea of a forum..

Edit: Typo

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Woo-hoo! I've learned so much in 15 minutes. We got our Fusion the night before starting a feature so I had no time to learn or play before getting up and running.

I noticed the inputs were weird compared to my 744, but attributed it to it being a new recorder... And I think that is definitely the case.

I consistently use the same receivers on the same input channels of my recorder. It is a compulsive habit of mine. I have have noticed different blocks of my Lectros can sound very different from one to another. I even just sent one in for repair as it seemed too far off from the rest (in my opinion very noisy). I was told nothing was wrong.  : /  Now I know. So, by using the same receiver in the same input, I develop habits and instincts. I wire certain voice types on certain blocks as I thinks scratchy voices sound awful on my yellow block, but the red block is a little warmer... Etc, etc.

But after getting the fusion, something has still been a little off with my input gains and I haven't been able to pin down why exactly. So, thank you Gabi for posting about this. It really started to make sense to the oddness. Things have been working fine... But I haven't been nailing things as much a I like.

Thank you, Billy, for your advice. That is exactly what I will do... And it should solve my problems. I rely heavily on my ears, which do a nice job monitoring levels. :))  but sometimes what I see and hear is a little more 'off' than I like and I worry when that happens. This will help my eyes and ears calibrate as well, I think.  :))

I will be checking and calibrating my Fusion soon and will report my results.

Thank you to everyone here for providing such an amazing forum for learning!!

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lol, Billy's logic is good for Billy too!  I've been using Deva's for ten years now and never have to worry about overload or excessive noise. 

And to respond to Peter, I (and many field mixers) quickly set trims by ear.  The only time I use tone is when I use radio mics.  Since the mic pre is in the transmitter (and set by ear, largely because every lav or plant mic has a wildly different output level) I want to confirm that the output levels of all the radios are the same so I generate -20 out of the receivers.  Each trim pot is in a slightly different position but that has never been a problem of concern to me.  It would be the same if I did a live 5.1 recording.  I'd set the trims by ear.  The audio gain into each mic would be different so I'd only be concerned that the background noise level was the same so there would be no pumping between tracks. 

Anyway, to each their own.  Gabi, before going into your machine, give Glenn at Zaxcom a call.  He'll advise what is possible or not.

All the best for the holidays!

Billy

Wow thanks Billy.  Do you set the inputs on the Deva to Mic or line? I always have mine at mic.  I should also mention I have 411a's.  I set my Fusion up similar to you but I like your idea with the trim.  I will try it out.

Gabi, I have not had this issue.  Mine might have a 1 or 2 db difference.  But like senator said its impossible to get the pots dead on to zero.

Sorry I can't offer anymore advice, I am also very new to Zaxcom products.

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Woo-hoo! I've learned so much in 15 minutes. We got our Fusion the night before starting a feature so I had no time to learn or play before getting up and running.

I noticed the inputs were weird compared to my 744, but attributed it to it being a new recorder... And I think that is definitely the case.

I consistently use the same receivers on the same input channels of my recorder. It is a compulsive habit of mine. I have have noticed different blocks of my Lectros can sound very different from one to another. I even just sent one in for repair as it seemed too far off from the rest (in my opinion very noisy). I was told nothing was wrong.  : /  Now I know. So, by using the same receiver in the same input, I develop habits and instincts. I wire certain voice types on certain blocks as I thinks scratchy voices sound awful on my yellow block, but the red block is a little warmer... Etc, etc.

But after getting the fusion, something has still been a little off with my input gains and I haven't been able to pin down why exactly. So, thank you Gabi for posting about this. It really started to make sense to the oddness. Things have been working fine... But I haven't been nailing things as much a I like.

Thank you, Billy, for your advice. That is exactly what I will do... And it should solve my problems. I rely heavily on my ears, which do a nice job monitoring levels. :))  but sometimes what I see and hear is a little more 'off' than I like and I worry when that happens. This will help my eyes and ears calibrate as well, I think.  :))

I will be checking and calibrating my Fusion soon and will report my results.

Thank you to everyone here for providing such an amazing forum for learning!!

In my Fusion, with the fader set to "0", to align the signal on the display, between inputs 3 and 6 (if the trim is true) there is a difference of 15dB.

Gabriel

post-1776-130815091621_thumb.jpg

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will the off-set between channels stay freeze once leveled to 0dB? Or does this vary from day to day? If it stays there could be an software option "set all trims to zero". That way one levels the particular recorder and after all is set the trims are set to "0" which makes it easier to set them back to an equal level after some changes were made.

I often record stereo-mic parallel to dialog scenes (street noise, crowd, FX). It would be very annoying if I can´t just plug into 2 channels, set them to equal trim, link faders and be sure to record a true stereo-image. I often wouldn´t even listen to that mics but concentrate on the production mix.

Matthias

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will the off-set between channels stay freeze once leveled to 0dB? Or does this vary from day to day? If it stays there could be an software option "set all trims to zero". That way one levels the particular recorder and after all is set the trims are set to "0" which makes it easier to set them back to an equal level after some changes were made.

I often record stereo-mic parallel to dialog scenes (street noise, crowd, FX). It would be very annoying if I can´t just plug into 2 channels, set them to equal trim, link faders and be sure to record a true stereo-image. I often wouldn´t even listen to that mics but concentrate on the production mix.

Matthias

These differences are not equal on all machines, is random, which makes it harder to solve the problem of all

units with a single firmware.

Gabriel

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Gabriel,

I think Matthias has a point here. There could be an "offset trim page" just to correct the input gain differences on each recorder. Once all the inputs are set to the same value, then we can use the trims to establish the relationship between our other devices and the recorder not to correct some hardware problem.

I hope Zaxcom is still reading this discussion.

Thanks, Matthias.

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