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Recommend a good mic preamp for measurements


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#41 lukeamdman

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Posted 16 June 2016 - 07:41 PM

Let me rephrase, when I looked at the calibration files for my Earthworks M30 and M50 mics, there wasn't any correction at the bottom end.  I think I remember reading that was pretty common for most good mics.

 

And I didn't find the UMIK to be very accurate at 90Hz so I'm not surprised that it has roll-off on the low end.

 

Ahhh gotcha!



#42 Ricci

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Posted 16 June 2016 - 07:54 PM

 

I've researched the roll-off of the 2i2 and I think this statement makes sense:

 

http://www.hifizine....e-scarlett-2i2/

 

"While it’s often recommended that loopback tests used to “calibrate” an interface such as this are performed with the microphone input, I’m not sure that is always correct. If the circuit has an output coupling capacitor, then the lower input impedance of the microphone input may affect the low-frequency rolloff (in a way that it will not be affected if a microphone is used as the source)."

 

 

 

Here's a frequency response strictly on the line/mic in:

 

http://johnr.hifizin...2-measurements/

 

 

 

That quote is absolutely true and often missed. There is often an impedance mismatch. The headphone output is usually better for the loopback though it may still introduce it's own effects.

 

Also Dave is right with the cheaper mics it is often the HF that really needs corrected most. The more expensive and trusted measurement mics are good enough to use without a cal file on the low end and often up to 18-20Khz. My rig is down a bit at 5Hz. I don't bother with a cal file at all. I know it's there but it's not enough to be worth worrying about. A lot of the cal files I've seen are questionable to say the least.


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#43 3ll3d00d

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Posted 16 June 2016 - 09:03 PM

As one of the articles I linked above mentioned, I'm not sure a loopback test from a line output in the 6i6 to its own mic input is the best way to determine the roll-off for just the mic input (my signal source won't be the 6i6 but rather my processors HDMI output).  There's going to be roll-off on the output that's then combined with the input's roll-off, not to mention the impedance differences from the line out vs. an actual microphone which also affects the frequency response.

Yes I know, there is certainly a difference in the measured result when you do mic input vs line input. However I said "on that test" in my post for a reason :) he uses a loopback from line output to line input and that's what I am describing in my post. So if 2dB at 5Hz vs 0.5dB at 5Hz is important to you then I recommend verifying your own signal chain with your actual equipment.



#44 lukeamdman

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Posted 16 June 2016 - 09:07 PM

Yes I know, there is certainly a difference in the measured result when you do mic input vs line input. However I said "on that test" in my post for a reason :) he uses a loopback from line output to line input and that's what I am describing in my post. So if 2dB at 5Hz vs 0.5dB at 5Hz is important to you then I recommend verifying your own signal chain with your actual equipment.

 

Sorry man!  My reading comprehension is tanking because of a lack of sleep (newborn in the house).  I can't imagine how the wife feels!


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#45 dgage

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Posted 16 June 2016 - 09:35 PM

Sorry man!  My reading comprehension is tanking because of a lack of sleep (newborn in the house).  I can't imagine how the wife feels!

 

I find kids are able to sleep better when they aren't trying to sleep next to 140dB in the next room though I understand how you might think the tactile feel might lull them to sleep anyway. :D


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#46 lukeamdman

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Posted 20 June 2016 - 04:08 PM

I just pre-ordered the 2nd gen 6i6 from Musicians Friend for $229.99 shipped.  Should ship around 7/1.

 

The specs say the max on the mic input is +8.5dBu but I also noticed it has a 10db pad that can be turned on.  Does that means it's really good for +18.5dBu, or is the +8.5dBu spec is with the pad already on?  I'll email them about it.



#47 lukeamdman

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Posted 22 June 2016 - 05:44 PM

Focusrite confirmed the mic input of +8.5dBu on the 6i6 is without the 10db pad engaged.  They're going to update their site/doco. 



#48 Ricci

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Posted 22 June 2016 - 08:47 PM

Focusrite confirmed the mic input of +8.5dBu on the 6i6 is without the 10db pad engaged.  They're going to update their site/doco. 

 

I kinda figured that would be the case.



#49 lukeamdman

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Posted 22 July 2016 - 09:21 PM

I'm getting some pretty funky loopback results from the 6i6.

 

First, a loopback from line out to line in with a TRS to TRS cable:

 

cap1_zpssnqecw0a.png

 

 

That looks fine to me.  A little more LF roll-off than I'd like but nothing glaringly wrong. 

 

Second, another loopback from line out to line in, but this time using a "combo" jack input on the front that accepts both TRS for line level inputs and XLR for mic inputs.  Still using the same TRS to TRS cable:

 

cap2_zpsklozpyeo.png

 

 

 

Uhhh....what the heck is that? 

 

Third, line out to mic in using a TRS to XLR cable:

 

cap3_zpsq8xi9tfs.png

 

Whoa....

 

 

All 3:

 

cap4_zpsudci29bt.png

 

 

 

I'm using ASIO in REW and a 48khz sampling.  The higher the sampling rate the worse it gets.

 

Any ideas?



#50 3ll3d00d

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Posted 22 July 2016 - 09:41 PM

your line in-out loopback looks like a mic input

 

here's my 6i6

 

cyan is line out to mic in (front combo jack)

red is line out to line in (rear TRS)

purple is line out to inst in (front combo jack)

 

comparison.png

 

the other measurements look like some sort of feedback. Can you show a pic of mixcontrol?

 



#51 lukeamdman

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Posted 22 July 2016 - 09:54 PM

your line in-out loopback looks like a mic input

 

here's my 6i6

 

cyan is line out to mic in (front combo jack)

red is line out to line in (rear TRS)

purple is line out to inst in (front combo jack)

 

attachicon.gifcomparison.png

 

the other measurements look like some sort of feedback. Can you show a pic of mixcontrol?

 

fc2_zpsul5dhh7n.png

 

fc1_zpsxrhg5smk.png

 

 

 

Besides the sampling rate this is basically all default settings. 



#52 3ll3d00d

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Posted 22 July 2016 - 09:59 PM

interesting, I didn't realise they had a new mixer app out (I'm still using mixcontrol). 



#53 lukeamdman

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Posted 22 July 2016 - 10:05 PM

interesting, I didn't realise they had a new mixer app out (I'm still using mixcontrol). 

 

Mixcontrol looks better than this.  New one is a very vague interface. 



#54 3ll3d00d

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Posted 22 July 2016 - 10:11 PM

actually now I see this is for the 2nd gen scarlett interfaces, is that what you have? mine is a 1st gen



#55 lukeamdman

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Posted 22 July 2016 - 10:12 PM

actually now I see this is for the 2nd gen scarlett interfaces, is that what you have? mine is a 1st gen

 

Yes, this is a 2nd gen. 



#56 lukeamdman

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Posted 22 July 2016 - 10:28 PM

Also, I RMA'd the first 6i6 I received after seeing the same results.  Focusrite tech support had no answer for it either and recommended the RMA.

 

I just got this one today and it's the same so...



#57 3ll3d00d

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Posted 22 July 2016 - 10:46 PM

Your mixer looks like you are sending a mix to the monitor output, the daw channel output is cut off the bottom of the pic though so not sure where that is going. Perhaps you can confirm?

I suggest you switch to direct playback and repeat your test anyway.
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#58 lukeamdman

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Posted 22 July 2016 - 11:26 PM

Your mixer looks like you are sending a mix to the monitor output, the daw channel output is cut off the bottom of the pic though so not sure where that is going. Perhaps you can confirm?

I suggest you switch to direct playback and repeat your test anyway.

 

You're onto something here...

 

"Direct Routing" mode

 

fc3_zpsuzaa82dd.png

 

 

Line out to combo in using TRS to TRS and "Line" setting:

 

cap5_zps25iqob35.png

 

 

Same thing but with the "Instrument" setting:

 

cap6_zpsq2xn49ey.png

 

Line out to mic in with a TRS to XLR cable:

 

cap7_zpskad8gp0d.png

 

All 3:

 

cap8_zpsercg2vjk.png



#59 SME

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Posted 23 July 2016 - 11:15 AM

Nice.  Glad you got that cleared up.

 

I had to re-read this thread because I'm looking at needing that analog phantom power source soon to plug my EMM-6 into my Motu A16.  But I guess everyone here is using a USB interface.  I could just try buying something cheap from Guitar Center or whatever, but I'd at least like to be able to measure whatever roll-off it has.  Is that possible if the roll-off depends on interaction with the mic itself?  Is my mic calibration from Cross Spectrum useless?  I was disappointed to see a lot more low-end roll-off on the EMM-6 than the UMIK-1, but I gotta have an analog mic to use on the Motu.  Hmm.

 

Edit: If I buy a cheap phantom power interface and I run a sweep with the UMIK, then I replace the UMIK with the EMM-6 without touching the stand and re-run the sweep, I can use the respective calibration files along the calibration for the Motu input to back-out the roll-off of the interface.  Ugly and not very accurate, but it can hopefully at least get me in the ballpark for < 10 Hz where I'm likely to have problems.


Edited by SME, 23 July 2016 - 11:30 AM.


#60 lukeamdman

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Posted 23 July 2016 - 03:25 PM

Nice.  Glad you got that cleared up.

 

I had to re-read this thread because I'm looking at needing that analog phantom power source soon to plug my EMM-6 into my Motu A16.  But I guess everyone here is using a USB interface.  I could just try buying something cheap from Guitar Center or whatever, but I'd at least like to be able to measure whatever roll-off it has.  Is that possible if the roll-off depends on interaction with the mic itself?  Is my mic calibration from Cross Spectrum useless?  I was disappointed to see a lot more low-end roll-off on the EMM-6 than the UMIK-1, but I gotta have an analog mic to use on the Motu.  Hmm.

 

Edit: If I buy a cheap phantom power interface and I run a sweep with the UMIK, then I replace the UMIK with the EMM-6 without touching the stand and re-run the sweep, I can use the respective calibration files along the calibration for the Motu input to back-out the roll-off of the interface.  Ugly and not very accurate, but it can hopefully at least get me in the ballpark for < 10 Hz where I'm likely to have problems.

 

My first 6i6 was definitely defective.  Output 3 didn't work, and even a line out to line in measurement looked crazy.  Also, trying to "reset to factory defaults" would cause a BSOD...

 

I recommend going away from the cheap USB mics or any mic that needs a calibration file for bass.

 

I sent my CSL calibrated UMIK to Josh to compare to his M30:

 

UMIK%20vs%20m30%20LOW%20BASS_zpsqchkvcvc

 

 

Even with a cal file it was still down ~4db more at 5hz than the M30 (no cal files).  Also, Josh had to offset the SPL for the UMIK because it was a few DB low as well.






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