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Author Topic: Wireless Mic System for measurements  (Read 20624 times)

Arthur Skudra

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Re: Wireless Mic System for measurements
« Reply #20 on: September 20, 2013, 02:07:30 pm »

Here is a loop through test of the Line6. And a pic to show that compare to a M23 on wire you have ca 15db less gain with a DPA 4060 and about 25db less gain with the Micw. So by not having a gain on the beltpack you have to increase the noise 15/25 db... not reallly optimal?
/R
Hi Rasmus,  Could you repost those jpgs at higher resolution/bigger size?  Very interesting!
So what you're saying is that the beltpack M23 is 25 dB less than a M23 on a wire?  Are you able to do some noise floor comparisons in spectrum mode?
Arthur

Edit:  It would be great to know the setup of your measurement (eg input gains) as well.
« Last Edit: September 20, 2013, 04:00:37 pm by Arthur Skudra »
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Gustaf Kempe

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Re: Wireless Mic System for measurements
« Reply #21 on: September 20, 2013, 03:31:44 pm »

But you have to test it that eay with 2 identical mics. I only loose 5dB compared to a wire. You don't have to do a TF to find out. Ju a spectrum and check the dB level in Smaart, first with wire then with Line6. If I would loose 25dB it would only be noise in my measurements, and it's not...
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Rasmus Rosenberg

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Re: Wireless Mic System for measurements
« Reply #22 on: September 21, 2013, 11:19:38 am »

But you have to test it that eay with 2 identical mics. I only loose 5dB compared to a wire. You don't have to do a TF to find out. Ju a spectrum and check the dB level in Smaart, first with wire then with Line6. If I would loose 25dB it would only be noise in my measurements, and it's not...

Evil kanivel... don't multi task and do forum posts, i guess is the lesson.

Oki sorry for the confusion, What my point with the pic was just to show that cutting the feature to be able to gain on the belt pack, is "sad", as two cheap and widely available mic's can't be used directly with the system, at least optimal or?.

I believe the root of my own confusion was that last time we tested was not with the M23. Or more likely we tested the M23 to a lower gain mic receiving less input and scratched the idea of making it work.   

So to clear up:
Yes, you can use the M23 on the line6 with a good Phantom power supply. I used the Denecke PS-1a, and only loose about a db of gain, and the Phase response up top are not match (as seen in the loop through), not too bad though.


/R
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Rasmus Rosenberg

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Re: Wireless Mic System for measurements
« Reply #23 on: September 21, 2013, 12:38:47 pm »

Oh I remember, about the sensitivity.
So in the field if you measure at low level fare form the speakers (good candidate for a WL mic) how do you compensate? Lets say if you had the mic on a wire you would gain 50db, the Line6 you can only boost the output 12db so major difference there, and the mic still see really little level, close to its noise floor or?
/R
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Arthur Skudra

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Re: Wireless Mic System for measurements
« Reply #24 on: September 21, 2013, 01:24:17 pm »

Oh I remember, about the sensitivity.
So in the field if you measure at low level fare form the speakers (good candidate for a WL mic) how do you compensate? Lets say if you had the mic on a wire you would gain 50db, the Line6 you can only boost the output 12db so major difference there, and the mic still see really little level, close to its noise floor or?
/R
Maybe I need to get some caffeine, but I'm still confused.  In the previous post to this one, you said you only lost about a dB of gain, and now you are saying that you are losing more with the M23 and the Line6 transmitter??  Sounds like some non-linearity in the measurement to me, unless I'm missing something!  :)
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Rasmus Rosenberg

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Re: Wireless Mic System for measurements
« Reply #25 on: September 21, 2013, 02:07:40 pm »

Maybe I need to get some caffeine, but I'm still confused.  In the previous post to this one, you said you only lost about a dB of gain, and now you are saying that you are losing more with the M23 and the Line6 transmitter??  Sounds like some non-linearity in the measurement to me, unless I'm missing something!  :)

He he well come to my world :)
I say that with the same gain on the I/O i loose about one db with the M23+PS1 (phantom supply)+Line6 output at 0db. Compared to a M23 straight on a wire.

Next im saying that the gain match between the Belt pack and the M23 is not IMO optimal, I can only in what i would consider normal conditions "hit" the belt pack with a low signal, one led lamp out of 5 (indicating signal). So if I used wired mic's I don't have to raise the output I could gain the balcony mic right? WIth the Line6 I can only boost the low signal hitting the mic 12db.
/R
« Last Edit: September 21, 2013, 02:24:30 pm by Rasmus Rosenberg »
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Arthur Skudra

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Re: Wireless Mic System for measurements
« Reply #26 on: September 21, 2013, 03:23:45 pm »

He he well come to my world :)
I say that with the same gain on the I/O i loose about one db with the M23+PS1 (phantom supply)+Line6 output at 0db. Compared to a M23 straight on a wire.

Next im saying that the gain match between the Belt pack and the M23 is not IMO optimal, I can only in what i would consider normal conditions "hit" the belt pack with a low signal, one led lamp out of 5 (indicating signal). So if I used wired mic's I don't have to raise the output I could gain the balcony mic right? WIth the Line6 I can only boost the low signal hitting the mic 12db.
/R
Ah, ok, makes sense now, essentially the gain stage between the specific microphone (the M23) and transmitter is not optimal, as can be seen by the low meter level on the transmitter.  But in the work that we typically do in live sound, does it really matter?  Let me elaborate...

In the context of live sound measurement, we typically deal with a very limited dynamic range in sound reinforcement systems (consider the noise floor of a typical shed with the ventilation system on, and the upper limit of the output of a system), so where do you think the noise floor has an *effect* on measurements when using the M23 with the line 6?  Stimulus at 60 dBA, 70 dBA, 80 dBA, 90 dBA and so on?  Perhaps the moral of the story is to measure with stimulus that is "loud enough" for the output of the microphone being used.  Here's where dual channel measurements work extremely well, we can see how the noise floor influences our measurement by keeping an eye on the coherence curve and making sure it remains high enough to do our work.

To quantify this, find a *really* quiet room (eg recording studio), and with everything quiet, measure the noise floor with the microphone wired direct to your computer interface's preamp (take a snapshot in spectrum mode).  Then measure it with the same gain on the computer interface, but now with the line 6 system inserted in the path.  Now take a snapshot of the noise floor in the spectrum mode.  This should give us an answer to the above question for that specific type of microphone and it's sensitivity rating, provided that the signal path remains linear with all our measurements.  To test for linearity, feed a stimulus in the system, and increase it by 10 dB increments, take a snapshot of the transfer function of each, then offset the curves on top of each other.  They should remain the same in frequency response as the level increases.
« Last Edit: September 21, 2013, 03:39:14 pm by Arthur Skudra »
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Rasmus Rosenberg

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Re: Wireless Mic System for measurements
« Reply #27 on: September 22, 2013, 07:36:16 am »

Ah, ok, makes sense now, essentially the gain stage between the specific microphone (the M23) and transmitter is not optimal, as can be seen by the low meter level on the transmitter.  But in the work that we typically do in live sound, does it really matter?  Let me elaborate...

In the context of live sound measurement, we typically deal with a very limited dynamic range in sound reinforcement systems (consider the noise floor of a typical shed with the ventilation system on, and the upper limit of the output of a system), so where do you think the noise floor has an *effect* on measurements when using the M23 with the line 6?  Stimulus at 60 dBA, 70 dBA, 80 dBA, 90 dBA and so on?  Perhaps the moral of the story is to measure with stimulus that is "loud enough" for the output of the microphone being used.  Here's where dual channel measurements work extremely well, we can see how the noise floor influences our measurement by keeping an eye on the coherence curve and making sure it remains high enough to do our work.

To quantify this, find a *really* quiet room (eg recording studio), and with everything quiet, measure the noise floor with the microphone wired direct to your computer interface's preamp (take a snapshot in spectrum mode).  Then measure it with the same gain on the computer interface, but now with the line 6 system inserted in the path.  Now take a snapshot of the noise floor in the spectrum mode.  This should give us an answer to the above question for that specific type of microphone and it's sensitivity rating, provided that the signal path remains linear with all our measurements.  To test for linearity, feed a stimulus in the system, and increase it by 10 dB increments, take a snapshot of the transfer function of each, then offset the curves on top of each other.  They should remain the same in frequency response as the level increases.

My concern might not be valid i will do some more test in the parking a lot tomorrow. And also try to find a quiet place to do the back ground noise.

The concern just came from memory,where I have put the mic in a fare away location, and received not thing but noise, because i hit the belt pack with so low volume. WHat could have thrown me off guard is that with the Micw or DPA i get the same indication on the receiver (one led, signal) as a M23, so if you test at home 1 mtr. from the speaker its easy to get decent signal through. But if you take it straight to the field, that -15/-25db starting point quickly comes into play. I can see on my interface that i was at least -20db lower gain on the wired mic when doing the test at home, than my standard measurement preset. So again sorry for the confusion, I didn't compare apples to apples, but interwoven the results into the workflow. Athurs point still remains, do I measure loud enough and its the mic sensitive enough to pick the signal up. My concern might not be valid as Athur explaind above, As im proberly blinded buy the fact that im lock at a lower gain, and have not come up with a valid test procedure to show the difference. I would be more confident if I knew I had a good strong signal on the belt pack, and not that I might be on the edge of the noise floor.. That was why I would like to get some data from Don, to how strong a signal the belt pack would like to see, and how that translate into mic sensitivity.
I will run some more test as soon as i get time. Thanks for the patience.
/R
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Rasmus Rosenberg

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Re: Wireless Mic System for measurements
« Reply #28 on: September 23, 2013, 09:22:22 am »

Did a test to day at about 17 mtrs. Guess the sensitivity is not much of a huge deal after all, at least not compared to having a good RF signal.
A few shots if I hit the belt pack with different level. 0db is the level of the M23. First is overlaid next it the individual.
/R

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Arthur Skudra

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Re: Wireless Mic System for measurements
« Reply #29 on: September 23, 2013, 04:34:53 pm »

Awesome stuff Rasmus!   :)   I see you got the quad display going in Smaart!   ;)
Just curious to know what SPL level was the mic measuring?
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ProSoundWeb Community

Re: Wireless Mic System for measurements
« Reply #29 on: September 23, 2013, 04:34:53 pm »


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