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Re: Calibration File Question about freq range 9 years 11 months ago #7909

  • john.reekie
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Finally an official response on what's happened!


To be fair to miniDSP, it's been only 3 days, during a time when miniDSP had officially announced that their office is closed...

www.minidsp.com/forum/2-announcements/78...w-year-holidays#7827

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Re: Calibration File Question about freq range 9 years 11 months ago #7910

  • thatsnasty
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I'm also wondering about the 20hz issue.
I just got mine in the mail and my speakers are measuring flat to 20-30hz (they have a 50hz highpass).
If the microphone is supposed to be flat, is this because of the cal file as well?

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Re: Calibration File Question about freq range 9 years 11 months ago #7911

  • curryman
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Not 100% sure about REW but normally calibration data will be simply extended to frequency range outside the existing data (e.g. below 20Hz). I won't expect any sudden jump below 20Hz so that should be a suitable way to go.

And to be honest: if you are finally wrong by 1 or 2 dB below 20Hz, you won't hear (feel) anyway ;)

General calibration should of cause be OK, but that will be handled soon as it looks like.

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Re: Calibration File Question about freq range 9 years 11 months ago #7912

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Given the Chinese new year holiday...the weekend and the time difference I think thats a pretty good service and we have a resolution.

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Re: Calibration File Question about freq range 9 years 11 months ago #7944

  • monomer
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The shape of the raw mic response (or the cal file) isn't relevant, it's only how the mic response measures when the calibration file is applied...

Unless you have other needs for a mic which doesn't have the capacity for applying a calibration file. The less calibration shown in a file means the more accurate your mic will be when used in those applications. So, yeah, to some of us it may well be quite relevent.

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Last edit: by monomer.

Re: Calibration File Question about freq range 9 years 11 months ago #7946

  • john.reekie
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I am curious to know what application you have that would require such accurate response without using a calibration file...

Anyway, with these sub-$100 mics (UMIK, Behringer, PE etc), the only way to get what you want would be to ask the supplier to specially select one for you. Even then, it might not be feasible. A more expensive mic like the Earthworks M30 is a more likely bet.

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Re: Calibration File Question about freq range 9 years 11 months ago #8020

  • devteam
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Dear All,

Hoping you had a good week end!
As promised our supplier supplied the new batch of calibration files this morning for SN# 190 and up. We just posted them this morning on the server so using the Text box in the product page, you'll be able to download the calibration file.

The previous file being incorrect as it was missing the 20Hz to 800Hz section from the file.
Note that SN# from 0 till 190 will be updated shortly this afternoon.

Sorry for the issue and thanks for your patience for this little mishap!

DevTeam
miniDSP, building a DSP community one board at a time.

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Re: Calibration File Question about freq range 9 years 11 months ago #8021

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I'm also wondering about the 20hz issue.
I just got mine in the mail and my speakers are measuring flat to 20-30hz (they have a 50hz highpass).
If the microphone is supposed to be flat, is this because of the cal file as well?


Do you know what order is that 50Hz highpass? could be first order and you wouldn't see it clearly on a graph. Could also be down to the measurement method. At low frequency, you may need to perform so called ground floor sub measurement. here is an example :http://www.synaudcon.com/site/author/pat-brown/measure-a-sub-place-a-sub/

Hoping this info helps.

DevTeam
miniDSP, building a DSP community one board at a time.

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Re: Calibration File Question about freq range 9 years 11 months ago #8022

  • devteam
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Finally an official response on what's happened! It sure sounds like good news to me that I won't need to return my UMIK for a re-calibration. Next week is not too long to wait for a corrected calibration file. About the only question I had that wasn't directly answered however is if the new calibration file will go below 20.1Hz?


@ Monomer,

Sorry for missing your question. The calibration will stop at 20Hz I'm afraid. We've found that below that, the supplier wasn't able to get a very reliable data so it's safer to provide accurate data from 20 to 20khz. However, from the measurements that you'll see online and comparison done with other mics (e.g. Earthworks), you'll see that the electret capsule behaves well without a calibration file.

Hoping this info helps.
DevTeam
miniDSP, building a DSP community one board at a time.

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Re: Calibration File Question about freq range 9 years 11 months ago #8023

  • monomer
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Well first off, I'm quite delighted you guys got those corrected calibration files up so quickly... Thank you for that.

...The calibration will stop at 20Hz I'm afraid. We've found that below that, the supplier wasn't able to get a very reliable data...

What does this mean? How come the first batch of UMIKs got reliable results enough to publish down to 4Hz? These UMIKs are specified to be accurate down to 15Hz @ +/-1dB.... are they or aren't they? I'm going to assume without any correction no one really knows... wouldn't it be more honest to simply amend those misleading specifications for accuracy?

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Last edit: by monomer.

Re: Calibration File Question about freq range 9 years 11 months ago #8024

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@ Monomer,

You're correct that the first batch had some calibration file down to 4Hz, but as per our previous post, we'll soon update that batch of file as well (SN# 0 to 190) to put back to the same formatting of data. Talking with the supplier, we realized that the initial set of calibration file could have a higher level of accuracy. So all mics will have the same formatting/consistency from now on based on the data we collected at the factory for all mics.

The +/-1dB rating is actually with the calibration file loaded and really how we can achieve that accurate data. You can see from the calibration file (similar electret as ECM8000/WM61/EMM6..) that these capsules are already very linear but still need some calibration by the time they are loaded on a microphone body. The real accuracy comes down with the calibration file (i.e. achieving a flat/accurate response).

We can indeed update the line in the specs of the frequency response. Good suggestion.

Hoping this clarifies.

DevTeam
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Re: Calibration File Question about freq range 9 years 11 months ago #8027

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I just saw that the older cal files (<190) have 3 values in a row, the new ones just 2? what is the difference?

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Re: Calibration File Question about freq range 9 years 11 months ago #8029

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I just saw that the older cal files (<190) have 3 values in a row, the new ones just 2? what is the difference?


The third column is the phase, which is part of the FRD format. However its usefulness for mic cal is doubtful and as devteam noted above, it will be removed in the revised files.

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Re: Calibration File Question about freq range 9 years 11 months ago #8040

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I'm also wondering about the 20hz issue.
I just got mine in the mail and my speakers are measuring flat to 20-30hz (they have a 50hz highpass).
If the microphone is supposed to be flat, is this because of the cal file as well?


Do you know what order is that 50Hz highpass? could be first order and you wouldn't see it clearly on a graph. Could also be down to the measurement method. At low frequency, you may need to perform so called ground floor sub measurement. here is an example :http://www.synaudcon.com/site/author/pat-brown/measure-a-sub-place-a-sub/

Hoping this info helps.

DevTeam


It's just my receiver's. Does this method work with any low frequency measurements?

Not sure if you were implying that I was measuring a subwoofer. I was measuring my mains that are definitely down almost to 0db at 20hz. Looking back now it could be because of the ambient noise in my room.

After cranking my receiver to -10 (and umik at 100%) I got a more accurate reading. This is painfully loud. I still find it strange how the lower frequency stuff is at a volume higher then where the speakers cut off.

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Last edit: by thatsnasty.

Re: Calibration File Question about freq range 9 years 11 months ago #8052

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Hi

All the UMIK-1's have the same sensitivity factor: -21.1dB. Is this another mistake by the company who did your calibrations?

Thanks

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