[ProAudio] Microphones question

[Dan Mills]

Ein is the input referred noise, so if you dial in say 60dB of gain,
and the reading on the output millivoltmeter is then say -65dBu then
you know the input referred noise (at that specific gain setting!) is
-125dBu.

How significant?
Depends on the use case, but getting within a few dB of the thermal
noise from the real part of the mic output impedance at full gain is
not that hard, so mostly it is a marketing number being far easier to
quantify then something like overload recovery behaviour which might
actually matter more.

What is far more interesting a lot of the time is what happens at 40dB
of gain rather then wide open, staying quiet there usually needs more
then a single stage or switched gain rather then a single reverse log
pot in the oh so common instrumentation preamp.

I tend to view Ein, as being much like THD+N, as long as it is low
enough, there are other things I care about more.

Regards, another Dan.

On Mon, Jun 14, 2021 at 4:06 PM Mike Rivers via ProAudio
<proaudio at bach.pgm.com> wrote:
>
> How about a little discussion on the value of knowing the EIN of a preamp and how the figure is useful to the designer?
>
> Here's why I ask:
>
> When I was writing reviews regularly, EIN was (and still is) often quoted in the product's specs. The numbers ranged from -125 dBu (just a couple) to a majority being either -127 or -128 dBu. Manufacturers liked to tout it because it was a nice low number with "noise" in its name. And it was always measured at a level within a dB or so of clipping since that's it looked the best.
>
> But unless I missed the appropriate chapter, EIN is a calculated value - the measured noise level with the gain subtracted out. So a preamp with 60 dB of gain that advertised EIN=-128 dBu could be expected to put out -68 dBu of noise, measured, of course to the advantage of the marketing department with the appropriate input termination (0, 100, or 150 ohms usually) and output load.
>
> So, among design engineers, what's the big deal about EIN? Is there a better way of measuring it that's more meaningful? And if you can squeeze another dB of EIN out of a design, how significant will this be to the user?  I
>
> , know "it depends."
>
> --
> For a good time call http://mikeriversaudio.wordpress.com
>
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