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Measure gain on mic inputs?

jtwrace

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#1
@amirm Would it be possible to measure the gain on mic input(s) for these reviews?
 

Rja4000

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#2
Which reviews do you speak about ?
Audio interfaces ?

The problem, when there is no analog pre out (there rarely is), is that there is no standard to define what 0dBFS means. You have to trust the manufacturer specs for that.
Therefore, it makes little sense to measure it.

What would make sense, though, is to give the level required to reach 0dBFS at max gain.
But that's not exactly the gain.
 

Blumlein 88

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#3
You can input a signal that gives 0 dbfs at max gain. Then reduce gain to the minimum setting and see what dbfs is recorded. This would give you the gain range of the device. Or you could use any other arbitrary level like -3 dbfs to make sure no clipping occurs.
 
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jtwrace

jtwrace

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Thread Starter #4

Rja4000

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#5
You can input a signal that gives 0 dbfs at max gain. Then reduce gain to the minimum setting and see what dbfs is recorded. This would give you the gain range of the device. Or you could use any other arbitrary level like -3 dbfs to make sure no clipping occurs.
Sure.
That would give you a gain range.
Thats interesting data.
But not absolute gain.
 

Blumlein 88

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#6
Sure.
That would give you a gain range.
Thats interesting data.
But not absolute gain.
In terms of the end user it effectively is no different. I don't know of any interface where it works any different. You'd have to be doing digital gain rather than analog. And that would deteriorate the EIN spec. I've only checked a few and they aren't doing anything weird in that regard.
 
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jtwrace

jtwrace

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Thread Starter #7
Doesn't it seem like a good thing to check for mics such as the Shure SM7B? I'm debating on what interface to go with for that mic.
 

AnalogSteph

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#8
It would be useful to have a system gain measurement à la Julian Krause. Turn DUT gain to max and determine what kind of generator level gives -6 dBFS or thereabouts (it is not uncommon to see linearity issues near 0 dBFS, but I don't think it gets any worse than the Behringer UMCxxxHD which should be run much beyond -5 dBFS or so).
JK gives a figure of xx dBFS @ 0 dBu, I think that's a bit clunky / abstract and would probably prefer dBu in @ 0 dBFS, which is a real tangible value. Numerically it's the same, just with an opposite sign, so comparisons would be super easy.
 

Blumlein 88

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#9
Looking at various mic preamps, nearly all are arranged so that -45 dbu to -50 dbu input at max gain will give you max input levels or 0 dbFS if they include an ADC. Generally those with higher gain levels allow higher input levels. The Forte was unusual in that -63 dbu would give 0 dbFS at max gain. One of the reasons it would be an excellent choice for an SM7b or for other insensitive microphones like ribbons.
 
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