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TOPIC: Re: Low quality design or faulty mic ?

Re: Low quality design or faulty mic ? 7 years 7 months ago #8711

  • georgio
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Hi Devteam !!

Thanks for the answer. There is no problem with the delay; I guess it happens. I hope you all had a nice time.

Also thanks for the replacement offer.
As I mention in my e-mail, I think that the issue at hand is with the "soundcard" portion of the device. I would like to see a clean input from it with no spikes. It's a shame that your electronics are limited to 74dbFS. 16 bits nowdays give you easily the theoretical 96db. And for the claimed 24 bits of UMIK-1 with input gain all the way down we should see at least that much.
Please post at some time a no signal (ambient sound level at maximum gain) against dbFS spectrum analysis.
If the improvement is not too much I will rather modify the mic myself.

On a general note, I think more people will benefit from a higher gain and lower maximum sound pressure level, but that's just my opinion.

And as a footnote, it's nice to see that your team is not afraid to acknowledge an issue and do something about it.

Regards

George
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Re: Low quality design or faulty mic ? 7 years 7 months ago #8733

  • georgio
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Hi again.
I have opened up the mic and had a go improving it. I must say that things are looking pretty good. Without the microphone transducer connected and a 2.2 kohm loading resistor in it's place, I got from the original -63db down to -90db (27db improvement). See the screenshots bellow.

With the microphone transducer in place, I get -88db noise/spike floor (it was about -68db for me).
It's not a very easy mod but still I did not have to use any active components (as was my initial intention).
If the guys from miniDSP are OK with it, I can post more details here; but I think that they have already solved it so there is no point. I just couldn't wait ;)

Cheers
George

Original spectrum with 2.2kohm instead of microphone transducer at the input :


Moded with 2.2kohm resistor instead of microphone transducer at the input:


Final result with ambient noise showing. -88.4 db for the nasty spikes :
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Re: Low quality design or faulty mic ? 7 years 7 months ago #8734

  • devteam
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Heheh.. indeed you couldn't wait..:-) We were preparing some instructions for you as promised but we realize that you were eager from the point we mentioned that you could fix it yourself.. It's great seeing that you figured it out. Great job George!

Do feel free to show your mods by any means.. We have no problems with it.
As a disclaimer, we just want to say that the tricky step here is to "open" the microphone. It's not very easy if you don't have a tool that has pin able to go inside the little holes. But with a bit of jiggling, it will move and open the mics. Inside you can have access to the internal DIP jumper to modify the analog gain.

We can document all this later for those of you wanting to do a modification. Modifying these resistors will mean modifying the internal input gain but it's a "known" gain difference. Just need to update manually the calibration file to account for that change. We can document all this later on.

DevTeam
miniDSP, building a DSP community one board at a time.
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Re: Low quality design or faulty mic ? 7 years 7 months ago #8742

  • georgio
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Hi again !

Please send your instructions as well, I will be glad to test them.
You certainly have inside info (ic's involved, pcb layout etc) which I had to partly and up to a point reverse engineer. So your solution should be optimum.
I will contact you through e-mail with a full report.

Regards
George
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Re: Low quality design or faulty mic ? 7 years 7 months ago #8745

  • ejh2854
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Good stuff- please keep the info coming-!
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Re: Low quality design or faulty mic ? 7 years 7 months ago #8758

  • miki_ada
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I've opened the mic too. With two nails and a flat pliers it's not a difficult task. Just cut the head of the two small nails, put them in the pliers and rotate the ring with the two holes. No scratches at all...
Dear George, what is your mod? I think that you've maybe modded the supply of the mic capsule... ? Can you explain you mod please?
Dear minidsp, I'll post the photos of the mic so other users can adjust the gain themselves.

Regards,

Michele
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