MiniDSP UMIK-1 Microphone - Page 83 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #821 of 887 Old 04-30-15, 09:15 PM
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Re: MiniDSP UMIK-1 Microphone

China actually, which is close enough...

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post #822 of 887 Old 04-30-15, 09:22 PM
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Re: MiniDSP UMIK-1 Microphone

Thanks for the info Wayne,
I was thinking maybe I pushed a wrong button when ordering.

I apologize if this subject had been breached already but this thread was a bit long to go through.
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post #823 of 887 Old 05-01-15, 06:12 AM
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UMIK-1 mic gain

Quote:
JohnM wrote: View Post
The gain figure in the UMIK-1 device name comes from the device itself, it indicates an internal gain setting (which can be altered by opening the device should there be a need, would be unusual).

Use Audio Midi Setup rather than Sound preferences to set the input gain and set it to 0 dB (per the help).

Select the input for the UMIK in the REW soundcard preferences rather than leaving it as "Default Input", that allows REW to compensate for any changes to the input volume setting (if running the REW beta version).

I'm struggling with this, John, I need to set the range to 0dB to allow higher SPL measurements in REW.

From the UMIK-1 datasheet: Max SPL for 1% THD @ 1kHz - 133dB SPL @ 0dB gain setting


I can clip the ADC running at only 95dBA pink noise. I'm presuming this is because of the 18dB mic-gain applied, but I can't find how to set it to the 0dB range.

"Use Audio Midi Setup rather than Sound preferences..." Is this in REW or an OS thing?
"...per the help" is this REW help, or from a UMIK-1 help file (which I don't have).

I'm on Win7-64.


I feel I'm missing something obvious...




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post #824 of 887 Old 05-01-15, 03:39 PM
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Re: MiniDSP UMIK-1 Microphone

The gain is set by switches inside the mic, there is a thread on how to do that here.
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post #825 of 887 Old 05-02-15, 11:52 AM
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Re: MiniDSP UMIK-1 Microphone

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The gain is set by switches inside the mic, there is a thread on how to do that here.

Thank you once again John.

I'd got to this understanding since my post, having wandered around the MiniDSP forums, but I didn't know the actual gain options and I hadn't seen any pictures. This is perfect -it makes me much happier to go exploring inside my own UMIK mic now. I want to analyse one of my PA rigs. I think I'm going to set it to 6dB after reading that thread, rather than 0dB.


I'm wondering if this gain is being set digitally by simple bit-shifting, as the steps are "6dB", ie a factor of two, one binary bit column. This wouldn't upset the capsule and analogue calibration, it would just be digital scaling -it would make sense as nobody seems worried about calibration issues while changing this sensitivity setting in the mic, including the manufacturer.


If this is the case, should we be amending the REW UMIK calibration sensitivity by 6.0208dB per step..?


thanks once again...



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post #826 of 887 Old 05-02-15, 01:17 PM
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Re: MiniDSP UMIK-1 Microphone

The gain settings in the mic are affecting the analog front end gain, to keep the REW levels displaying correctly the sensitivity figure in the cal file needs to be adjusted correspondingly - so if you set the switches for 6 dB instead of 18 dB for example, subtract 12 dB from the sensitivity figure.

The Windows volume control applies digital gain adjustment over a span of -31 dB to +24 dB (the span and resolution is set by the device itself). As long as the input has been selected in the REW soundcard settings (not just left as default) REW compensates for the effect of the digital gain so SPL readings are not affected by the volume control setting.
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post #827 of 887 Old 05-03-15, 03:41 AM
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That would explain why the input level graph seems to change while adjusting the Windows gain, but the SPL seems to correct itself once the gain slider stops changing.

It seems to be a good idea to not give this gain value any positive value to avoid eating into the signal-chain headroom. Is this correct?



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post #828 of 887 Old 05-03-15, 07:41 AM
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Re: MiniDSP UMIK-1 Microphone

Yes, there isn't any benefit from using levels above 0dB since S/N isn't improved. By default REW sets the volume control to 0 dB.
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post #829 of 887 Old 05-04-15, 04:29 AM
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Just for clarification John, does REW change the actual value that the Windows mic level slider normally controls, or does it apply a correction value to it? I'm just trying to understand the signal chain/ logic of the USB mic input.

There seem to be option tickboxes in Win7 to allow applications to control levels, but the REW input level (dB FSD) suggests that doesn't happen and it is corrected afterwards.

I have been prodding about with this REW/UMIK combination and already found in my case that adding the mic after the program is running can upset the correction logic, resulting in incorrect SPL values. I would like to understand the system and root out any pitfalls like these before I use it in anger -without a second SPL meter I wouldn't have been sure that I'd broken the level control/compensation.

Thanks for bearing with me...



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post #830 of 887 Old 05-04-15, 07:16 AM
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Re: MiniDSP UMIK-1 Microphone

Quote:
planetnine wrote: View Post
Just for clarification John, does REW change the actual value that the Windows mic level slider normally controls, or does it apply a correction value to it? I'm just trying to understand the signal chain/ logic of the USB mic input.
If the box is checked on the REW soundcard preferences to allow REW to control input volume and the volume setting is less than the 0 dB level REW will raise it to the 0 dB level when the input is first selected, otherwise it leaves it alone. Whether REW has set the volume or not, it monitors the volume setting and adjusts the SPL readings to suit.

It is best to plug in USB soundcards before REW starts up, Java only refreshes the audio device lists every minute or so. Make sure the cal file is still loaded.
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