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Mic Level or Line Level?


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I'd like to re-introduce a subject that is of particular interest me currently and it pertains to gain structure in the wireless workflow from talent mic to camera send.  I have always been told to output from Lectro receivers at a low level and to input to the recording device (recorder or camera) at mic level.  In a past post, reproduced below, John Blankenship makes a convincing argument against this and I'd love to hear further discussion.

JB Post:

For instance, let's say you are running a mic into a mixer, from whichyou have a line out cable into the Lectro transmitter and then goingmic level from the receiver into the camera...  Here's whatyou are doing signal-wise:  Your mic is feeding into a low level preampin the mixer which boosts the signal up to line level...then, thatsignal is attenuated at the input of the Lectro transmitter where the,once again, low level signal is AGAIN feeding a low level preamp whichis amplified to the point where it modulates the transmitter and thesignal is sent to the receiver which then amplifies the signal to aline level and then you are attenuating that signal back down to a miclevel, where, AGAIN it feeds a low level mic preamp which boosts itback up to line level to feed the camera's operating circuits.Mostof us are aware that the single most critical amplifying stage is a lowlevel (mic level) preamp.  It operates down near the circuit minimumswhere noise, RFI, and gremlins lurk.In the above scenario, byfeeding the camera's mic input, you are now going through THREE lowlevel amplification stages, amplifying the signal to line levelfollowing each one, and then attenuating the signal back down into thesubsequent stage.  If I were writing a White Paper on "How To Damage AnAudio Signal," the scenario of repeatedly attenuating a line levelsignal to mic level and then amplifying it back up to line level, stageafter stage, would be one of my prime suggestions.Lectroreceivers always operate at full gain in the output stage.  The levelcoming out of the Lectro receivers is then either left at that fullgain or is attenuated via a passive resistor network down to whateverlevel the operator sets it at.The simple answer:  Always run a Lectro receiver at max gain out unless it's absolutely necessary to do otherwise.Robert,I don't like the sound of Lectro's limiters, either.  They're a "brickwall" type of limiter that isn't gentle to the signal.  They are thereprimarily to prevent over-modulation (a big no-no).The bestadjustment point I've found with Lectro transmitters (for units UM200Cor later -- UM200B and earlier were calibrated differently ) is to pushthem until the limiter light just occasionally flickers on peaks -- butnot too frequently.Experiment.  Listen.  Make sure that whenyou're trying different level settings of the transmitter that you'readjusting the input of the camera with the corresponding reciprocaladjustment so you're not just hearing the camera being hit withdifferent internal levels.

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What I am saying is that if you have to have the camera level controls wide open to get a -20dbfs reference level going in at line level, you'd be better served to change the input on the camera to mi

I have read all the post and i think i help out in cleaning up some seriously but understanding of audio gain staging. 1- Let's be really clear, Gain staging is NOT about listening and hearing if

Don't over complicate it.   1. You set the transmitter gain properly. 2. Max the receiver output. 3. Line input to the MixPre. 4. Gain up the channel until your meters are whe

I think something that matters here is the camera circuitry. 

If the camera is set for line level, is it simply attenuating the input and sending it through the same pre amp circuitry it would be going through at mic level?  What exactly does the knob adjustment on the camera do, affect the input gain or the output to "tape" level?

I have discovered, on the EX1 for example, that if you max out the Letro 411 and go in at line level, then the "fader" or knob on the camera needs to be virtually maxed out for a near appropriate level.  If the knob is set at '5', which is marked in white on the camera indicating what I imagine is the suggested setting, and mic level is used, then -25 on the Lectro 411 seems to get the "correct" level on the camera when tone is sent via the mixer to the Tx at -20dB.

Perhaps the next experiment at David Waelder's house can be testing noise levels on the final "tape" when each method is used.

Robert

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"   I have always been told ...  "

by who??

and not always, as JB has informed you otherwise...

what did Lectro tell you??

and in addition to JB's excellent observations, keep in mind that in any transmission line, a signal measured in thousandths of a volt is much closer to any little noise that might also be picked up in that line, (this is called a low signal to noise ratio!), and a 1 volt (line level) signal traveling on the same line will have a much greater s/n ratio; at mic level, the noise might be "heard" along with the audio, but the same amount of noise is totally buried at line level.

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I have ALWAYS run Lectros at Line level into either the Cooper and now the Cantar. I have seen a lot of people here running the Lectro at mic level going into their mixers with the preamp in line. Whatever JB says is correct.

 

There's something called gain staging. And this is certainly inappropriate gain staging.

Apropos gain settings on the Tx, I have had an exchange with Larry Fisher in the past, in which he clearly points out that the Tx should be set to OPTIMUM level, and not very low. This is another thing i have seen people do here, their Tx is always around 9 o'clock, and rarely more than 10 o'clock on the knob. In fact, if you read the UM400 manual for example, this fact is clearly explained.

If the gain staging is properly set up, one should not need to have more than ONE preamp in the signal chain after the microphone. Of course, assuming all the gear is professional grade. :)

-vin

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By Line level do you mean +4?

I have ALWAYS run Lectros at Line level into either the Cooper and now the Cantar. I have seen a lot of people here running the Lectro at mic level going into their mixers with the preamp in line. Whatever JP says is correct.

There's something called gain staging. And this is certainly inappropriate gain staging.

Apropos gain settings on the Tx, I have had an exchange with Larry Fisher in the past, in which he clearly points out that the Tx should be set to OPTIMUM level, and not very low. This is another thing i have seen people do here, their Tx is always around 9 o'clock, and rarely more than 10 o'clock on the knob. In fact, if you read the UM400 manual for example, this fact is clearly explained.

If the gain staging is properly set up, one should not need to have more than ONE preamp in the signal chain after the microphone. Of course, assuming all the gear is professional grade. :)

-vin

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Eric:

Thanks for the succinct response.  I was sort of trying to "bump" the thread to get more responses about whether folks a) output from lectro at low level and input (to camera or recorder) at mic level or, B) output from lectro at higher (line) level and input at same, and why.

A.

"0" output and up is line level. "0" is .775vac, +4 is 1.25vac. No mic pre amp required.

Eric

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I notice that when I run my Lectro 211s at full line level (+9 or +10) into my SD 302 I end up with the trim pot around two oclock or higher with the fader at 12 o'clock or higher.  This is with actual voices.  If I turn on tone from the receivers the trim pots are around noon, and the faders are around noon to get a zero reading on the 302 meters.  The 302 inputs run through the same circuit whether its set to mic or line and in the Lectro information they say if going mic level into a mixer they suggest a -30 level.  If I do that, I'm able to use less of the trim pot to get the level I'm looking for on actual voices.  I always run my meters on the peak/hold setting and I like to see them range from +8 to +12 on the mixer.  This corresponds to around -6 to -9 on the digital camera's meters.  For the transmitter I always start between one and two o'clock on the mod knob.

So in this situation and this gear, is it better to go line in or mic in?  Discuss.

Bernie

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Just recently used a D4 receiver on a panasonic camera (P2 full size camera with 5 p2 slots on the side....the model name/number escapes me right now)

When outputing at + 8 (highest setting on the D4 receiver) from the Receiver to the camera set to line level, even with the rotary dials on the camera fully open, I couldn't get enough level to hit -20 on the meters. So I had to go with mic input to attain proper levels.

Was I doing something wrong ?

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The output level that you set on the Lectro RX corresponds to full modulation at the transmitter.  This is the maximum level before limiting.  This explains why a hot mic level is used, or why folks can't seem to get enough level from the line level settings.  Notice if you set you 411 RX to a proper mic level setting like

-46dbu into a mic level input you will notice the signal to be quite noisy.

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I'm not sure I understand the question.  If you're asking if one or two people (out of the many hundreds here) have given an opinion then the answer to your question is yes.  Is that what you're asking?  Kindly clarify.

Arnold, isn't the 'why' already answered consummately?

-vin

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Mike:

Call Lectro and then report back to us.  Also, I think we'd all find it illuminating to hear how you handle this workflow.  I'm dying to know.

A.

what happens when you feed the D4R to other gear, say a mixer set to accept line level inputs??

" Was I doing something wrong ? "

I'd be curious to know what Lectro says...

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Just recently used a D4 receiver on a panasonic camera (P2 full size camera with 5 p2 slots on the side....the model name/number escapes me right now)

When outputing at + 8 (highest setting on the D4 receiver) from the Receiver to the camera set to line level, even with the rotary dials on the camera fully open, I couldn't get enough level to hit -20 on the meters. So I had to go with mic input to attain proper levels.

Was I doing something wrong ?

I doubt you were doing anything wrong. I bet if you hard wired to the camera at line level from your mixer with the same camera settings you'd see smoke coming out of the camera, it would be that hot.

One other thought that may not apply is that if the rx output is unbalanced it will be 6db lower going into a balanced input. The extra gain provided by a mic preamp in the camera more than compensates for the level drop that happens when going line level in.

Eric

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So what you are saying, Eric, is that all is ok if the camera's meter reads well below -20db, even if the "volume" knob on the camera is cranked all the way, and the 411 receiver is at +5 (maximum setting), and when it is clear on the Tx and Rx and mixer that -20bd is what is being sent?

That just seems odd to me.

It seems to me, unless I am wrong, that all line/mic switches in most gear is an attenuation of the signal before being sent through the very same circuitry a mic signal is sent.

How is sending a hot signal into the camera, where it is attenuated and then sent through the pre amp and then boosted further by cranking the volume knob, any better than sending an attenuated signal from the receiver into the camera where it goes straight into the pre amp and the volume knob rests at a normal position?

Robert

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Lectrosonics receivers do not output a traditional pro-audio  line level.

The standard line level outputs on pro- audio equipment are typically 0dBu or +4dBu = OVU and Digital -20dBFS. Above this operating level will be 20dB of headroom as pro analogue electronics output a maximum +20dBu to + 24dBu.

Lectrosonics receivers output a maximum of around +5dBu (411) to + 8dBu (Venue). If the transmitter is set for a nominal signal level 20dB below limiting, the signal output will be around -15dBu. This is primarily done to reduce power consumption in battery powered receivers.

Lectrosnonics receivers practically output what would be described as a low level line signal or a high level mic signal.

David M

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Lectrosonics receivers do not output a traditional pro-audio  line level.

The standard line level outputs on pro- audio equipment are typically 0dBu or +4dBu = OVU and Digital -20dBFS. Above this operating level will be 20dB of headroom as pro analogue electronics output a maximum +20dBu to + 24dBu.

Lectrosonics receivers output a maximum of around +5dBu (411) to + 8dBu (Venue). If the transmitter is set for a nominal signal level 20dB below limiting, the signal output will be around -15dBu. This is primarily done to reduce power consumption in battery powered receivers.

Lectrosnonics receivers practically output what would be described as a low level line signal or a high level mic signal.

David M

The question is what to we do with this "odd" signal that is too low for line level but too high for mic level?

I feel that if we are feeding a camera that simply attenuates the input when the line/mic switch is set for "line", then we might as well attenuate the output of the receiver, set the camera for "mic" level, and record a proper level of signal on the camera.  As posted by me and several others, setting the 411 at -25 in the menu, switching the camera (Sonys) to "mic" and having the camera levels set in the middle seem to yield levels which match the mixer.

Robert

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I'm just gonna say as long as you give a listen to it and it sounds good, then does it really matter?  I always try to keep it at line level as much as I can, but when it comes to my Lectros and going into my mixer I prefer the way they sound through my 442 at mic level.  I find I have to turn the gain up higher on my 442 inputs at line level and it seems to be just slightly noisy(hisssss).  The mic level helps me to deal with noisy locations as well as I can leave the tx gain lower and push the rx output in mic level.

J Hemmerlin

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From what I can gather from my limited knowledge of reading schematics, the 442 (and presumably all other SD units) as well as the PSC Solice have no difference in where the signal goes whether "line" or "mic" is selected on the input.  If "line" is selected on the input, the input signal is attenuated to mic level and then sent on its way as if it were a mic level signal.  I don't expect cameras to be constructed in any other way.  But if anyone has access to the schematics of the cameras we see most often, we can all get that information.

Robert

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There's a lot of misinformation and misunderstanding in this thread.  I don't have the time to give it the depth the subject deserves, but here's a capsule:

Read my earlier notes on the Lectro receivers.  Circuit-wise, they operate at full output at all times.  I haven't looked into the new four channel unit, but for all the others I'm aware of, this is the case and it has been confirmed repeatedly by Larry Fisher, both to me personally, and to many others on various newsgroups.  The adjustable, and lower level outputs are simply attenuated via a balanced passive attenuator.

It has been suggested that my former writing was "opinion."  While that may be true for certain operating preferences, it is not true for the laws of physics.  I didn't create the universe and I didn't determine those laws, so please, don't shoot the messenger.  It's still true that the sun rises and sets each day and it's also still true that a mic level signal amplified to line level is subject to more noise, distortion, and phase nonlinearity, than a line level circuit. That's why one of the most telling tests of a mixing panel is how the mic inputs sound.  Just because someone may not understand those laws of physics doesn't invalidate them.

Several people have commented on circuit design with an obvious lack of knowledge of circuit design.  Yes, many circuits may use most of the same components for both line and mic inputs, but how those circuits are designed makes all the difference in the world.  Solid state gear (more than fifty years now) often has an open circuit gain of well over 100dB which then has inherent oscillation and other potential problems.  That's just too much gain for most practical audio use.  Amplifier stages are, therefore, optimized via the application of what's called negative feedback which gives them the proper gain for their chosen use and affords more stability.  So, yes, the same circuitry can be used for both mic and line inputs, with the difference being the amount of gain the circuit is set for.  This is a MUCH different scenario than simply padding down a line input to mic level. 

When this circuit is designed using components in common, the better manufacturers (think Sound Devices, etc.) will choose components that are optimum for use as a low level amplifier, and that also work well at higher levels.

However, with some manufacturers (think camera makers) if there is a compromise in this "common circuit" approach, the compromise is more likely when it is used as a mic input, since high quality low level amplifiers are more costly to implement.  So, the assumption that this approach compromises the line input, and therefore the mic input is superior, is pretty well bass-ackwards.  If they simply pad down a line input to mic level, that's a different story.  That's just, plain bad design!

And, please, (and I mean this in the kindest way) if you're going to quote a full text of something someone else wrote, do them the courtesy of maintaining the formatting.  A large thick block of text with jammed together sentences is tedious to read, made even more difficult when addressing a technical subject.

I gotta get some sleep -- it's been a grueling shoot.

John B.

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I've always used a cable to camera with a return feed. Sending a signal from one unit to another( mixer to camera / recorder) at Line level. The important thing for me is head room and signal to noise ratio. But what I also do is try and run the camera inputs at 'full ball' and gaffer tape them like that so there is no bumping of the input gain from the operator handling ( especially on smaller cameras). This way also it gives me all the headroom I need on the mixer( at my end of the chain). The only time I've use wireless is for guide tracks as I really feel that camera are built to record visuals and that the sound circuits are left to second best in the overall design of cameras. But anyway I run at line level with the only preamp (mic to line convertion) stage being on the mixer input. If I had to use the Lectros ( which I haven't before ) I would send a balanced feed on a cable to the camera for callabration and then add the lecrtos with those callabration setting as a start. Working back wards I would properly also 'whack' the RX unit as much as possible (but properly not as hot as the camera input) and leave the remaining headroom on the TX unit. I would also still record a backup on a real sound recorder ( 24bit) and use pip's if no timecode is possible ( like on the eX1) to sync with the camera ( maybe try and set the ABS code on both machines the same and free run the days work).

The harder part for me is to go against what I mentioned about when I run from my 302 to my 702T. Running it at Line level would be my norm but then I miss out on all the EQ padding on the recorder and other option settings. So I find it harder to callabrate at mic level outputs from the 302 to my recorder. Any suggestions / tips ?

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...Running it at Line level would be my norm but then I miss out on all the EQ padding on the recorder and other option settings. So I find it harder to callabrate at mic level outputs from the 302 to my recorder. Any suggestions / tips ?

I don't have a 702T.  What are you referring to with the term  "EQ padding"?

BTW, I don't run Lectro wireless quite how you mention.  The best application of proper gain staging is to adjust signal level at optimum for each component in the chain, and, ideally, for each amplifier stage within each component in the chain.  Different components have different parameters.

For instance, if a Lectro's max output is +8dB, then the nominal level (i.e. RMS -- also meaning where you would set tone) would be served well at -12dB which would give the Lectro 20dB of headroom.  Lectro's specs are at maximum modulation which sometimes people stay too far below.  Wireless operation is one situation where proper gain staging sometimes becomes more elusive, yet even more critical.

John B.

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Thanks for the brief John

your posts are really informative.

I've just ordered 2 Lectrosonic units and should get them at the end of the month. I will test all the boundaries and different calibrations for sound quality then. Unfortunately in South Africa it's buy first ask questions later.

When I switch the SD 702T to line input the EQ setting are not assemble on the recorder. the SD 302 mixer has either 80Hz or 120/150Hz I think, where the recorder has more frequencies and attenuation for those frequencies and more frequencies lower and higher, that I like having use of. But I have to set the output of the mixer to mic level It seems. And therefore find the calibration settings between the two units more involved. Unless I get into the manuals and find a proper setting to run line out and mic in ( unorthodox I would imagine).

perhaps you could give me some pro's and cons to running a recording system like this at mic level.

Regards

Greg

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Regarding the Panasonic cameras.

After having some noise issues feeding the camera (HDX900) a mic level from wireless receivers for a reality show, I switched to line level and was also having trouble getting tone to reach -20dB on the Camera meters, even with transmitters operating fairly hot as per Lectros instructions (-20dB light flickering red occasionally on peaks)

There is however a camera menu setting which adjusts line input gain and with that gain increased I was able to get reference tone and peaks to the right levels.

I am shooting with the P2 varicam tonight with a wireless hop, and will try and get some more precise info about the settings that work.

JC

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