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Recommend a good mic preamp for measurements


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#1 dgage

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Posted 14 May 2015 - 02:08 AM

I am trying to become the next Ricci, OK, that's not accurate but I do want to take better measurements.  And while I know better equipment won't make up for knowledge, process, and experience, I need a better microphone preamp.  For microphones I'm covered with the Earthworks M50 and M30.  For a preamp I currently have a RME Fireface 800, but I'm hearing some noise in the output signal, even at moderate volumes so I'm starting to research its replacement.  I actually went to Guitar Center tonight and picked up the Focusrite Scarlett 2i2 preamp and I'll use this in the short term and it will be my backup in the long term.  I know Josh Ricci uses the PreSonus Firebox, which he says won't clip until at least 140db, but that one is firewire and discontinued.  I'd like to get a similarly capable preamp that is USB based, fairly recent, and will work in Windows 8.  I'd appreciate any recommendations.  Thanks.

David


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#2 mojave

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Posted 14 May 2015 - 02:55 PM

You will get the best results if both the preamp and the audio device share the same master clock - especially if you do any active crossovers. If you don't need 24 outputs, then sell the 24ao and get the MOTU 1248 instead which has 12 outputs and includes 4 mic preamps. If you want to keep the 24ao, then I would recommend getting the MOTU Ultralite AVB. You can connect it to your 24ao with an ethernet cable and they will by synced together and work as one device. You can take the Ultralite AVB elsewhere and easily use it for measurements. It will double as a good desktop DAC and can even be used in a 5.1 system. If you call Musician's Friend, you can get it for about $600. 

 

Like all MOTU audio devices, its analog output is DC Coupled for output to 0 Hz. You can connect to a laptop and subwoofer and be assured of no signal rolloff from the audio device measurements. The input will be cap coupled, but the MOTUs are flat to 3 Hz on the input. You can also control them with your phone or tablet which can be handy for making level adjustments during measurement sessions.

 

The 24ao plus the Ultralight are actually about the same price as the 1248.



#3 mojave

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Posted 14 May 2015 - 03:16 PM

Here is a loopback I just took with REW on my MOTU 1248. It is -2.5 dB at 3 Hz on the mic input.

 

MOTU 1248.jpg

 

 



#4 Ricci

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Posted 14 May 2015 - 03:47 PM

Hey Dave,

My needs are a bit different than most since I actually require the ability to measure at above 135dB often. If you are looking at performance testing your products you'll need to ensure a bit of headroom in the mic pre's over the biggest units you might end up making. Once you get into this long enough you probably won't want a larger 8+ channel unit either. You end up paying extra for unused channels and having something smaller and more portable is nice. Get the larger dedicated unit for a stationary install or recording work where you actually need the channel count. YMMV. Short of testing them yourself you can look at the mic preamp specs listed by the manufacturer if interested in potential headroom limitations and such.

 

 

Mojave I briefly looked at the UltraLite Motu product you mentioned but couldn't seem to find a basic specifications page on the web site or in the user manual?



#5 mojave

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Posted 14 May 2015 - 04:10 PM

The Earthworks M30 and M50 both have a sensitivity of 30mV/Pa. They also have a maximum acoustic input of 142 dB. 

 

The MOTU devices have a maximum input of +24 dBu on both the line and mic inputs.

 

On the chart below from Rane, you go down the left column to 30 mV/Pa and then go right to 142 dB. This equates to a maximum input level of +20 dBu. Therefore, the Earthworks mics and MOTU combo will be fine up to 142 dB with the MOTU having some extra headroom.

 

n148t1.gif



#6 Ricci

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Posted 14 May 2015 - 04:31 PM

+24dBu thanks...Is there a full spec page?

 

One more question. Do the knobs have detents? The UltraLite-Hybrid mk3 might be the unit I'm looking for.



#7 mojave

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Posted 14 May 2015 - 05:12 PM

Ricci, I just saw your question about specs. On any MOTU AVB product page, the tech specs are  available at the top right just to the left of Buy Now. I can't find tech specs either for the older products like the UltraLite-Hybrid MK3. 

 

The knobs on the AVB series have detents and you get a digital readout of the actual level. I'm not sure about the UltraLite-Hybrid Mk3, but assume it also has detents. The Ultralite AVB is an updated version of the UltraLite-Hybrid Mk3.

 

The AVB series use ESS Sabre chips for their output with the exception of the Ultralite AVB. The mixer on the AVB series is great and the ASIO driver is multi-client. You could have two different measurement programs taking simultaneous measurements. 



#8 dgage

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Posted 15 May 2015 - 02:50 AM

Thanks Mojave.  It was weird that you knew I had a 24Ao but such are the interwebs. :)  The plan was always for that to be for distributed audio so the mic preamp would be separate but I definitely like the AVB interoperability.

 

I like the look, size, and price of the Ultralite AVB...do you know if it gives up any performance to the 1248 in the mic preamp section, which is my primary focus right now? 


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#9 dgage

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Posted 15 May 2015 - 02:59 AM

Hey Dave,

My needs are a bit different than most since I actually require the ability to measure at above 135dB often. If you are looking at performance testing your products you'll need to ensure a bit of headroom in the mic pre's over the biggest units you might end up making. Once you get into this long enough you probably won't want a larger 8+ channel unit either. You end up paying extra for unused channels and having something smaller and more portable is nice. Get the larger dedicated unit for a stationary install or recording work where you actually need the channel count. YMMV. Short of testing them yourself you can look at the mic preamp specs listed by the manufacturer if interested in potential headroom limitations and such.

 

Thanks Josh.  Yes, I'm really looking to be able to replicate your testing and CEA 2010 for my own benefit and documentation.  My customers expect me to post output numbers and/or graphs and I want them to be as accurate as I can make them, following established standards and test methodology.  I don't want the data I post being refuted by anyone.  With your reputation, if I can get close to replicating your results, then I'm confident my results will stand up to any scrutiny.


David Gage
Deep Sea Sound
"You don't listen to our subs, you EXPERIENCE them!"


#10 chrapladm

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Posted 21 May 2015 - 06:44 AM

Hey Dave,

My needs are a bit different than most since I actually require the ability to measure at above 135dB often. If you are looking at performance testing your products you'll need to ensure a bit of headroom in the mic pre's over the biggest units you might end up making. Once you get into this long enough you probably won't want a larger 8+ channel unit either. You end up paying extra for unused channels and having something smaller and more portable is nice. Get the larger dedicated unit for a stationary install or recording work where you actually need the channel count. YMMV. Short of testing them yourself you can look at the mic preamp specs listed by the manufacturer if interested in potential headroom limitations and such.

 

 

Mojave I briefly looked at the UltraLite Motu product you mentioned but couldn't seem to find a basic specifications page on the web site or in the user manual?

Ricci if your interested I could sell you my Motu Hybrid Mk3. Mine has been sitting here for a while and I was planning on selling it whenever and then buy the 1248.

 

Dgage you have the Motu thread you started on AVS and Mojave and others all posted there so most of us know what you have. :D


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#11 SME

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Posted 12 February 2016 - 05:17 AM

I'm resurrecting this thread because I have a Motu A16 with 16 analog ins and outs but no phantom +48V mic inputs.  I think it would be convenient to do measurements through an A16 input so I can benefit from using the same clocks for input and output.  As such, I'm looking for a good mic pre-amp that's strictly analog with a flat response well down to the ULF.

 

Any thoughts?



#12 dgage

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Posted 12 February 2016 - 05:30 AM

What about something like the Earthworks B30 mic with built-in preamp? Not familiar with any analog only preamps but I'm not in the know on that sort of thing normally.

And I'd also like to say I have the Focusrite 2i2 for quick measurements and it does well, pretty much the same results as the Motu 1248 I also have. Really good deal for $100-$150.

David Gage
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"You don't listen to our subs, you EXPERIENCE them!"


#13 SME

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Posted 12 February 2016 - 06:00 AM

Actually, after doing a bit more Googling, it looks like I don't really need a pre-amp so much as a "phantom power supply".  They appear to be fairly simple devices and appear to be available in many different brands for very little money.

 

The catch is that because phantom power is transmitted over the signal lines, the power supply devices necessarily use capacitors to isolate the DC power from the signal.  So of course, there is low-end roll-off.  How much surely depends on the product and is probably not specified in the published specs.  I had the thought that I could measure and compensate for the roll-off of the power supply device, but unfortunately, it looks like the phantom power voltage will cook most line outputs, particularly those that are DC coupled.

 

Update: it looks like AS016 might be helpful here, but it requires registration to access.  I'll try to check it out tomorrow if I have more time.


Edited by SME, 12 February 2016 - 06:15 AM.


#14 shadyJ

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Posted 16 February 2016 - 06:26 PM

Hello,

 

kind of related to this, anyone know how to check how much dynamic range a microphone input has? I have a Behringer U-Phoria UM2, I would like to know how much loudness it can take. Will I just have to run progressively louder sweeps until it compresses? 



#15 Ricci

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Posted 16 February 2016 - 09:23 PM

The microphone should have a few specifications such as sensitivity and maximum SPL it is made to work at. The microphone preamp/ interface should also have sensitivity, maximum input level, etc. From these you can calculate what the rig should be able to handle. The limit is whatever component has the lowest ceiling. Might be the mic or the preamp. It is best to verify it if possible if absolute certainty is needed. Sometimes the clip indicators are off a bit and clipping might occur a bit before or after the indicators on your preamp if it has them. I prefer to have the preamp interface clip a bit before the maximum rated level for the microphone.



#16 shadyJ

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Posted 16 February 2016 - 11:19 PM

Thanks, the product page says 130 dB of dynamic range, but it doesn't have a straightforward specification page. My mic is rated for 140 dB I believe.



#17 Ricci

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Posted 17 February 2016 - 04:26 PM

What mic do you have?

 

I could not find any real specifications on the Uphoria with a quick search at Behringer or otherwise.



#18 shadyJ

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Posted 17 February 2016 - 08:51 PM

I am using the Earthworks M23, which supposedly has 140 dB of dynamic range, which I trust is likely an accurate spec. The Behringer Uphoria UM2 has this line buried deep in their marketing blather: "XENYX preamps offer a staggering 130 dB of dynamic range, with a bandwidth that extends from below 10 Hz to well above 200 kHz." A loop feedback test I did of the Uphoria is actually not bad for a $30 sound card, I believe it was only down something like 1.5 dB at 10 Hz. 



#19 Ricci

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Posted 18 February 2016 - 05:01 PM

Odd not to be able to find any actual specifications. They must be somewhere on the site. Looks like the only way to verify the amount of headroom will be manually. That's actually quite easy if you have a signal with a known SPL(dB) such as from a calibrator. Most measurement programs or even recording software will indicate how much headroom is left in the recording chain.



#20 shadyJ

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Posted 19 February 2016 - 12:57 AM

I do have a ND-9 Calibrator. How would you recommend I use it to find out the dynamic range of the Uphoria sound interface?






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