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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

Hi Billy,

Let's remember it is a logarithmic scale, so 6 dB is not really inconsequential. But let's assume it is. As I would normally work, I would compensate such a difference (let's assume I didn't line up to the tones on my Lectros and that I am adjusting by ear) by riding my faders or changing the gain of my transmitters. A 15 dB difference as Gabriel has found on his Fusion could make me open too much of my tx gain and cause my recording to be severely affected by the tx limiter, for example. Or on the other hand, could make me not open the gain enough and mess up with my gain structure resulting in a poor noisy recording.  If I can trust my inputs to be "dead on zero" or very close to that I can be sure that the place to make an adjustment is the TX, not the input trim. I shouldn't be riding my trims when recording from wireless receivers all set to line level...

I also ride my trims all the time to compensate for variations on different microphones, voices, performances and situations, but such a difference on the input gain just made me very confused.

I do not intend to touch my Fusion circuits in any fashion. Don't worry.

Thanks,

Gabi

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Every analog mic preamp has a trim. In most cases this is a pot. The pot is set to a position by the sound mixer. No 2 pots are ever in exactly the same position. This is exactly the case here with the addition of a numerical value that shows the pot position. We are not going to change the software as the other 99.9% of all Deva and fusion users would be effected. This system and menu has been fine for about the last 7 years. If any preamp is out of our +/- 3 dB spec the unit can be sent in for service and we would be happy to take care of it. I want to be as helpfull as possible on this but other than a input or two out of the 8 on the machine being out of specification there in nothing wrong in the design or implimentation of the input. In fact many would argue no preamp in a portable device can match the sonic performance of the Deva/Fusion input for Noise and distortion.

Please contact us directly if you wish to arrange for service.

Glenn

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One more thing that might make all feel better. Using an identical source level, when the input trim is adjusted so that the inputs are reading the same level in the trim menu. All inputs are exactly identical in all aspects at that point no matter what the offset number is.

Glenn

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We are not going to change the software as the other 99.9% of all Deva and fusion users would be effected.

Glenn

if it would be an additional option in the menu to set all trims to the value "0" after leveling is done not a single mixer of the other "99.9%" would be effected because no one would be forced to use that option. It is just easier to set all inputs to the same value rather than to -6, 11, -2, 7 and so on.

Matthias

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Every analog mic preamp has a trim. In most cases this is a pot. The pot is set to a position by the sound mixer. No 2 pots are ever in exactly the same position. This is exactly the case here with the addition of a numerical value that shows the pot position. We are not going to change the software as the other 99.9% of all Deva and fusion users would be effected. This system and menu has been fine for about the last 7 years. If any preamp is out of our +/- 3 dB spec the unit can be sent in for service and we would be happy to take care of it. I want to be as helpfull as possible on this but other than a input or two out of the 8 on the machine being out of specification there in nothing wrong in the design or implimentation of the input. In fact many would argue no preamp in a portable device can match the sonic performance of the Deva/Fusion input for Noise and distortion.

Please contact us directly if you wish to arrange for service.

Glenn

    Glenn,

Thanks for continuing this discussion.

About  direct contact with the Zaxcom, I, before posting here,

sent messages to the support and directly to  Collen, without any reply.

Tks,

Gabriel

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A little clarity, please for me (and this has nothing to do with trim pots), "gabi" and "gabriel" are two different people, right? I did not realize this. I thought that Gabi just changed her name as used here. You are both located in Brazil, yes? Sorry if I have offended anyone assuming that Gabi and Gabriel(a?) were the same person.

-  Jeff Wexler

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A little clarity, please for me (and this has nothing to do with trim pots), "gabi" and "gabriel" are two different people, right? I did not realize this. I thought that Gabi just changed her name as used here. You are both located in Brazil, yes? Sorry if I have offended anyone assuming that Gabi and Gabriel(a?) were the same person.

-  Jeff Wexler

Hi, Jeff,

My new name: Bié (Bié = Gabriel)

Bié

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if it would be an additional option in the menu to set all trims to the value "0" after leveling is done not a single mixer of the other "99.9%" would be effected because no one would be forced to use that option. It is just easier to set all inputs to the same value rather than to -6, 11, -2, 7 and so on.

Matthias

I totally agree.  I always try to have mine set to the same.

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A little clarity, please for me (and this has nothing to do with trim pots), "gabi" and "gabriel" are two different people, right? I did not realize this. I thought that Gabi just changed her name as used here. You are both located in Brazil, yes? Sorry if I have offended anyone assuming that Gabi and Gabriel(a?) were the same person.

-  Jeff Wexler

Jeff,

We are two different people. Gabriel Gomes (aka Bié) is a sound mixer based in São Paulo, Brazil. He has more than 30 years of experience as a sound person. He also runs a rental house of his own and he is very respected in our community.

My name is Gabriela Cunha (aka Gabi) and I've been a regular on this forum for a while. I must confess I never took the time to write on "who am I today" and introduce myself. I am 36 years old and have been a  sound person for the past 15 years (5 as boom operator, 10 as sound mixer).

We both live in São Paulo, Brazil and we are the only two sound people in the country that own Zaxcom products. Brazil is pretty much a "Sound Devices market" because there are no Zaxcom dealers around here.

I can't see how you would have offended anyone just by expressing your opinion on a subject.

Gabi

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I can't see how you would have offended anyone just by expressing your opinion on a subject.

Gabi

Thank you for clearing this up. My comment about offending was just because I may have referred to Gabriel as 'she' since I thought it was you. I do know who you are since you are a long term member of both this Discussion Group and CinemaSound. I fully understand the frustrations being the only ones with Zaxcom product in your country and no local dealer support, that is one of the reasons I wanted to help out in this matter (Glenn told me that Zaxcom does not have a dealer in Brazil). I hope this all gets sorted out to yours and Bie's satisfaction and I am confident that Zaxcom will help you get things right.

-  Jeff Wexler

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Hi Peter,

Gabi reported a 10 db difference, but the screen shots he included showed a 5db difference.  I checked one of my Deva 16's yesterday and found a 5db spread.  I also found that there is a bit of leeway on the trim pots.  You can turn it a couple of degrees before the meter responds. 

Moot point for me.  Once the trims are roughly set I cannot hear any difference between the channels.

As for comparing the settings on a Cooper to a Zaxcom, the Zaxcom trim pots are digital controllers and do not pass any audio (as an analog trim pot on a Cooper does).  If the pot passes audio there is more chance of introducing noise so a gain difference has more chance of being heard.  I for one cannot hear a 3db difference when the noise floor is -120 or something like that.  (And before you protest, I say 3db because the Zaxcom specs are + or - 3db which means some of the inputs can be 3db quieter than stated.  I'm guessing we are only concerned with the inputs that are 3db noisier.

Thanks for the holiday wishes.  Same to you!

All the best,

Billy Sarokin

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Hi Justan,

For my cart deck I use mic level inputs for my 2 Audio Ltd rf mics, line level for my Zaxcom radios, 2 digital inputs for playback feeds and 1 spare input that I use either as a mic or line in as needed.  My over the shoulder/car rig Deva is used more with mic level inputs.

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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I believe Zaxcom decided on the photo cell system for the pre amps because they were extremely quiet and eliminated the digital stepping that can occur if trims and faders are adjusted quickly.  I think the 3 db difference among the pre amps is due to the specs of the photo cells (Glenn, correct me if I'm wrong).  THe engineers at Zaxcom decided that the possible difference in gain between mic pre amps was a fair price to pay to get extremely quiet and linear pre amps.

Billy

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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Hi Gabi,

I use the tone generators on my receivers to align them all on the Deva.  Once they are set up I switch my trim pots over to Zaxnet control which locks the gain setting.  Setting up receivers is always tricky for precisely the situation you mention.  You want to make sure you have the gain set correctly on your mic pre-amp, which in this case is on the radio transmitter.  The tone output on the receivers eliminate the receiver output and Deva input gain as variables.

btw, the 15db spread the was posted is out of spec and indicates a factory repair is needed.   

Billy

Hi Billy,

Let's remember it is a logarithmic scale, so 6 dB is not really inconsequential. But let's assume it is. As I would normally work, I would compensate such a difference (let's assume I didn't line up to the tones on my Lectros and that I am adjusting by ear) by riding my faders or changing the gain of my transmitters. A 15 dB difference as Gabriel has found on his Fusion could make me open too much of my tx gain and cause my recording to be severely affected by the tx limiter, for example. Or on the other hand, could make me not open the gain enough and mess up with my gain structure resulting in a poor noisy recording.  If I can trust my inputs to be "dead on zero" or very close to that I can be sure that the place to make an adjustment is the TX, not the input trim. I shouldn't be riding my trims when recording from wireless receivers all set to line level...

I also ride my trims all the time to compensate for variations on different microphones, voices, performances and situations, but such a difference on the input gain just made me very confused.

I do not intend to touch my Fusion circuits in any fashion. Don't worry.

Thanks,

Gabi

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  • 4 weeks later...

if it would be an additional option in the menu to set all trims to the value "0" after leveling is done not a single mixer of the other "99.9%" would be effected because no one would be forced to use that option. It is just easier to set all inputs to the same value rather than to -6, 11, -2, 7 and so on.

Matthias

As I recent purchaser of a Fusion 10, I would love to see this in the next update more than anything. 

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