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Author Topic: Understanding Microphone Preamplifier Noise (link)  (Read 297 times)

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Offline huskerdu

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Understanding Microphone Preamplifier Noise (link)
« on: January 03, 2018, 07:22:43 PM »
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Offline voltronic

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Re: Understanding Microphone Preamplifier Noise (link)
« Reply #1 on: January 03, 2018, 07:43:29 PM »
This is really great, thanks for posting.

The proper measurement technique has been explained here before by Jon and a few others, but it bears repeating.

This bit was news to me:
Quote
The very best EIN that can be achieved is -133 dBV, since this is noise purely from a 150 ohm resistor.

I also see that SD is now listing EIN for the MixPre series in both dBV and dBu.  Previously, they were only using the better-looking dBV figure.
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Offline DSatz

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Re: Understanding Microphone Preamplifier Noise (link)
« Reply #2 on: January 04, 2018, 09:31:27 AM »
The article talks about using a 150-Ohm resistor as a surrogate microphone when measuring preamp noise, and matching gain levels when making any comparisons. It is indeed completely senseless to judge a preamp by turning its gain all the way up and listening with nothing connected to its input.

What the article doesn't mention is that the equivalent input noise of a preamp also varies considerably at different gain settings. It's not just that there is a fixed amount of input noise that is amplified more when you turn the gain up; in fact, equivalent input noise is generally lower at higher gain settings. That's why most manufacturers specify it at maximum gain.

The next layer to add to this understanding would be to realize that most actual microphones are significantly noisier (at least in some part of the frequency range) than either a 150-Ohm resistor or the input of a good preamp. But complicating the issue, the levels of noise in both sources vary considerably at different frequencies, as does the ear's sensitivity to noise (see https://en.wikipedia.org/wiki/Equal-loudness_contour). And the dynamic character of noise--its moment-to-moment variations--matters a great deal, too.

Then finally, consider live recording environments. Again, all the different variables come into play--frequency and time distribution of the noise--and again, environmental noise (especially in live, public situations) nearly always "swamps" microphone noise. So the environmental noise is generally greater than preamp noise, which in turn is generally lower than microphone noise. Thus the search for the quietest preamp can easily become an exercise in misplaced perfectionism (see https://en.wikipedia.org/wiki/Streetlight_effect).

--best regards
« Last Edit: January 04, 2018, 10:18:03 PM by DSatz »
music > microphones > a recorder of some sort

Offline aaronji

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Re: Understanding Microphone Preamplifier Noise (link)
« Reply #3 on: January 09, 2018, 09:21:15 AM »
I also see that SD is now listing EIN for the MixPre series in both dBV and dBu.  Previously, they were only using the better-looking dBV figure.

As long as SD noted the proper units (which they did), I don't see them looking different at all.  Especially since it is such an easy conversion, even for the mathematically-impaired...

Offline voltronic

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Re: Understanding Microphone Preamplifier Noise (link)
« Reply #4 on: January 09, 2018, 07:29:55 PM »
I also see that SD is now listing EIN for the MixPre series in both dBV and dBu.  Previously, they were only using the better-looking dBV figure.

As long as SD noted the proper units (which they did), I don't see them looking different at all.  Especially since it is such an easy conversion, even for the mathematically-impaired...

I agree completely, but there was a bit of a dustup on the GS Remote board accusing SD of engaging in marketing stat-fluffing.  Not worth linking to; it was ridiculous.
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