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Mic Sensitvity
by kevenk on 2011-10-13 22:23:44

With even moderate vocal levels, signal distorts.  Capsule sensitivity is at least 10dB too hot. I cannot find any way to adjust this.

Please advise.



Re: Mic Sensitvity
by dboomer on 2011-10-14 08:38:51

The capsule itself is nearly identical to a  SM58 sensitivity wise.  You are correct that there are no adjustments available but they are not needed.  If you are managing to actually overdrive the capsule you need to be micing something VERY hot.  We couldn't come close with vocals, kick drum or stuck in the bell of a trumpet.  If the singer is cupping the ball of the mic then that would do it ... but that would be happening before any electronics so a pad will not correct his condition.

I suspect that your trim controls are not set correctly.  If you were to plug in an SM58 (or similar) and set things so the input was correct and then unplug the mic and plug in the receiver ... the level should be the same to within about .5dB.  If your trim/gain controls are calibrated then I would suggest that somewhere between 25-30 dB of gain to be in the ballpark



Re: Mic Sensitvity
by kevenk on 2011-10-20 13:00:19

How does a setting downstream of the overloading/distorting device make any difference?  If it is pegging the meter on the Line 6 receiver and distorting at the output of the LIne 6, then what downstream device is going to reduce the distortion?

Singers are experienced professionals with good mic technique, usually on stand, rarely hand held.

As for comment about gain structure - it is uninformed since there are so many variables involved with the output stage of the SM58 in question and the input to the mic preamp - effective input impedance, interconnect, preamp's frequency vs. gain characteristics, etc.

Up till now I was considering replacing all my Sennheisers with Line 6's, but if this indicative of Line 6's support, I may have to choose something else.



Re: Mic Sensitvity
by dboomer on 2011-10-20 17:04:06

Sorry ... I made the gain structure assumption based on what I know about the XD-V that may not seem so obvious whithout that understanding.  You are correct that a downstream setting cannot fix a problem earlier in the chain. But if you are hearing distortion then the singer is crushing the capsule itself or it is happening inside the mixer (which was why I referenced the similarity to a wired SM58).

If you are overdriving the capsule there is no remedy except to get more distance from it (same as with any mic). You cannot overdrive the A/D converter inside the transmitter as it is protected with a hard limiter.  Because the system is digital, you cannot overdrive the front end of the receiver.  It always sees the exact same level regardless of a whisper or a scream .. it is data not audio and the modulation of the radio is always the same as well.

If you are concerned that because the top LED is lighting up you don't need to be.  The LED fires at -18 dBfs so there is a long way to go before you hit the limiter.  The LED is not an indicator of distortion.

The other possibility is defective hardware ... but that seems not to be the case based on what I gather here.

What mixer (or mic pre) are you running into?  Where is the trim/gain set on it?



Re: Mic Sensitvity
by Line6Tony on 2011-10-21 08:14:17

Marking this question answered, as DBoomer is more qualified to answer this than Customer Support, who usually addresses threads marked as questions. Please feel free to continue the conversation.



Re: Mic Sensitvity
by kevenk on 2011-11-10 14:53:24

This anomaly definitely sounds like pure and simple capsule overload more than anything else.  It does not sound like limiter induced distortion.

As for the down stream device, it is irrelevant and again assumes I do not know how to operate my equipment or have any concept of signal path and gain structure - truly insulting and nothing do with the problem I am experiencing.

As for the receiver audio signal meter being somehow equivalent to -18dBfs at its indicated top or highest LED- cannot begin to say how much is just plain wrong with this, starting with that the meter itself may be inducing some of the distortion I am experiencing.  The fs part of dBfs means full scale and therefore does not seem to be understood by Line6.  What good is a meter that has some otherwise random offset/de-rate - it is not so much a meter but some pretty lights that go up and down with signal level.  What sort of ballistics does this meter have if in fact its top LED is many dB below a max?  OY!

The more I dig into this the less I am inclined to purchase any more Line6 product.  The frustrating thing is the device is so close to being the right tool at the right price.  It needs a way to set mic sensitivity beofre the AtoD, like every other professional wireless mic and a proper audio signal meter that adheres to some metering standard.  With those changes Line6 might have an unbeatable combination.



Re: Mic Sensitvity
by Detonator on 2011-11-11 07:37:59

I have 6 of the xd-v70, and the gain on the units is essentilly the same as a wired mic.  I A-B'd a unit with (all wired models) an sm 58, beta 58, beta 57, om6, om7 (which is a low gain mic) and with the exception of the om7, there was no significant difference in output, and the "models" on the Line 6 were surprisingly close to the respective wired units.  No test equipment was used, the mics were very close in output.

I suggest you perform a comparison with a wired mic or two, and if you are still having this extreme gain difference, you have a functional issue with the Line 6 which probably requires service or replacement, my opinion. 

I'm very happy with the performance of these mics and have had no issues with any of them.

-Tim Tyler

Detonator Sound

Message was edited by: Detonator (spelling)



Re: Mic Sensitvity
by dboomer on 2011-11-13 16:22:06

Keven .... that is likely the case if you are hearing distortion.  You have overloaded the mic capsule itself.  If there were a pad after the mic capsule it would not correct this problem as the capsule would already be distortion and a pad would just lower the level but not correct the distortion.  If you are managing to "crush" the capsule the only cure is to have the singer get further away ... exactly as you would have to do with ANY microphone.  That kind of distortion must be prevented before it becomes an electric signal.

There is a hard limiter that prevents the A/D converter from ever clipping, but you will have so overdriven the mic by the time you get there that the signal will be completely unusable.



Re: Mic Sensitvity
by kevenk on 2011-11-17 13:12:23

Hi Tim,

Thanks for the reply.

My issue is with signal quality, not overall level or gain - Line6 are the ones trying to bring level/gain issues into the discussion.

With further usage, I have noticed that the top LED on the signal level indicator (based on Line6's admissions, it is not a meter of any sort of standard) on the receiver rarely ever lights, yet noticeable distortion begins when the second or third LED from the top lights.

FYI, all of this is using the XDV70 in L6-DC7 mode.

Keven



Re: Mic Sensitvity
by kevenk on 2011-11-17 14:07:48

FYI, all of this is using the XDV70 in L6-DC7 mode. I cannot tell from the documentation whether the capsule itself is dynamic or some form of condenser.

In any case, on other professional wireless mics, there is a sensitivity adjustment on the transmitter side.  The actual circuitry is adjusting the power transfer between the actual capsule circuit and any preamp or mic conditioning circuit in the transmitter prior to conversion in Line6's case, or compressor in analog companding systems.  The power transfer circuit is typically a simple resister network that switches varying amounts of attenuation between the capsule output and the next element in the electrical signal path.

As for the continuing comments about mic to source distance, I will say for the umpteenth time, all users are experienced pros.  No one has "crushed" the capsule.  These types of responses show an utter disrespect or lack of reading comprehension or both.

With further usage, I have noticed that the top LED on the signal level indicator (based on Line6's description, it is not a meter of any sort of standard) on the receiver rarely ever lights, yet noticeable distortion begins when the second or third LED from the top lights.  Part of the problem might that the signal quality is so good below these levels and so bad when distortion occurs. Whereas using an actual SM58, for example, the signal quality at moderate levels is just about the same as when driven hard so the difference in signal quality is not that noticeable.

As for the limiter you mention, I assume this is hardwired, non-user-defeatable in the transmitter circuit.  However the way you describe the  limiter operation, it seems it is more a word length waster than a limiter and might be in fact the very thing I am hearing and or artifacts of it.  Why would a hard wired brick wall limiter ever be calibrated for anything less than the MSB (somewhere between the equivalent signal level of 0dBfs and -6dBfs) which in turn would be calibrated to the max signal level accepted by the A to D?

Does the Environment Filter use the same gain reduction circuit as the limiter?  This could also be a source of distortion.

It seems to be that Line6 lack a basic understanding of gain structure, word length vs. dynamic range, metering. I don't think this is the case because the system sounds excellent with middle to lower levels - clean, clear, full, low noise.  I do think there may be some confusion, lack or communication or coordination amongst designers, technicians, engineers, etc.

Again, make just a few corrections to the product line and it could be a world beater - no one else is making a wireless system like this for even 6 times the price. But, it has to have standard audio signal level metering and sensitivity adjust at the transmitter.



Re: Mic Sensitvity
by dboomer on 2011-11-18 10:58:06

Hey K

The capsule is dynamic.

Other "professional wireless mics" have a sensitivity adjustment because they have such limited dynamic range.  Our system has no need of one because it is not possible to overload the input of the preamp or the A/D converters without first overloading the mic element.  Lowering the sensitivity could only result in more noise in the system.  You might make the case with the beltpack if someone were to plug in something other than a microphone ... but a "live sound" mic just can't do it.

I wouldn't expect anyone (other than complete misuse of the mic) to be able to sing loud enough but an experienced pro ... and even then not many have the pipes to do it.

Metering means something different than maybe what you are used to.  But since our signal is digital it really has no bearing to sound quality.  With conventional analog wireless you need to monitor the signal to watch for overmodulation in the radio.  With our system the modulation is always 100%, loud signal, quiet signal, no signal.  So the meter really only let you know that the channel is active.  It can't clip so there are no worries here either.  It's just different than anything else.

There is no "word length wasting" ... only a limiting at max voltage.

The environment filter and the A/D -  D/A limiting are not related at all.  The environment filters can cause some degridation to the signal if the conditions are right, but I've never heard them with someone singing ... only with speech if someone  gets too far off the mic.  They can be switched off and out of the circuit if you arre worried.



Re: Mic Sensitvity
by kevenk on 2011-12-01 14:06:46

re: Sensitivity adjustment, word length, brick wall limiting -

First, the assumption that a transducer's dynamic range adequately accommodates all acoustic conditions has been proven false many times, especially with microphone capsules.  Therefore, conditioning circuits are used to make the appropriate adjustments, including changing the load on a dynamic capsule for a better match to acoustic levels. 

Second while it is true the the theoretical dynamic range of a 24 bit linear AtoD is 144dB, actual thermal noise for something close to a humanly survivable temperature limits the maximum dynamic range to 124dB, wasting over 3 bits of a 24bit data word before any real world active circuitry is involved.  Therefore adjusting and or conditioning the signal level prior to the A to D affects signal quality, downstream digital and analog gain stages, and metering.

Third, I would gladly exchange lower distortion for higher noise anytime anywhere, especially if I have adjustment and control over the amount of the tradeoff - it is what audio engineers do day-in day-out when adjusting signal level - be it a trim, a pot or a fader.  In this instance I have a noticeable distortion level that I have no control over no matter how low the noise might be.  And distortion is dynamic and therefore more noticeable to the ear than a constant noise which the ear effectively ignores.

Fourth, the assertion that only an extremely loud singer could overload at the transmitter makes my case that either my unit is broken or that there is a design flaw. The mic has been used by experienced professionals who have good mic technique.

re: Metering -a meter is a meter when there is a standard or documented relative operating level (0 = ?dB?) and standard ballistics (VU, Peak, PPM).  What this XD-V unit has is a fancy signal indicator - it goes up when louder and down when softer but it is NOT a meter by any usual definition a meter.

re: audio signal level vs. modulation of other analog wireless units: all current professional systems use modulation and transmission systems that are largely audio signal level independent and have done for decades.  The mic/transmitter sensitivity is used to orient acoustic/mic signal level relative to the compander system for best audio performance. In the same way, this unit should allow the user to adjust sensitivity relative to the A to D to best match the acoustic and mic signal level conditions for best signal quality.

re: meters inducing distortion, I have seen it a million and one times in "all digital" systems and any combination of analog and digital systems - if the "sample" of the signal used for metering is not carefully isolated / buffered from the actual audio source, the action of the meter/meter circuit can and does introduce noise and distortion into the audio path being metered and vice versa.

Environment filter: the distortion I am experiencing occurs whether the environment filter is on or off.  If the distortion is AGC circuit induced, it is from ever the expanding list of such circuits being revealed through this dialog - my count is at 3 so far - which begs the question for a 24bit/48k system, why would these AGC circuits be necessary in deference to cleaner, simpler user adjustable gain stages?

At this point, I feel I have tried all I can on my end and can assume my unit is just broken.  What do I do to get it fixed?

And, please consider changing the design so that these Line6 units can be the perfect tool at the perfect price.  As it stands now, it is bit of a toy.



Re: Mic Sensitvity
by dboomer on 2011-12-01 17:20:17

Have you tried switching to a different mic model.  Please try the OM5 model and let me know it the problem persists.

btw ... there are zero AGC circuits in the audio of the system.




Re: Mic Sensitvity
by kevenk on 2011-12-09 01:18:51

Will try the OM5 emulator.

If there are no AGC's, then how is limiting and gating ("environment filter") accomplished? - AGC is the general term for an automatic gain control circuit which includes specific types like VCA's, opto-attenuators, etc.  Again, not confidence inspiring.

Keven



Re: Mic Sensitvity
by dboomer on 2011-12-09 08:03:54

There are no limiting circuits either (other than a voltage regulating circuit that protects the converters from over-voltage and is not in the audio chain).  Strickly speaking, there is no gate in the environment filter ... it is a downward expander which is done in software.



Re: Mic Sensitvity
by kevenk on 2012-01-26 13:36:57

Still waiting for LIne6 to tell me how to get my mic fixed?

Been a loonngg while -

I also have a standing call in to local Guitar Center to corral the Line6 rep when he or she is there.



Re: Mic Sensitvity
by dboomer on 2012-01-27 09:59:19

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