[ProAudio] Microphones question

[Dan Lavry]

I think you are confusing things. EIN does not need to be measured at full scale, and it is a real representative of the noise contributions.Micpre noise is low and not easy to measure directly. Say you test system can measure down to 1uV, but your signal is 0.1uV. It would be difficult to measure the noise directly.  Say you set the gain at 60dB, the noise will become 100uV, and a 1uV system can measure that. At 40dB gain you get 10uV, still good enough to measure. In the first case Ein is 100uV/1000, in the second case 10UV/100, both yield 0.1uV which is the real input noise.Of course that will not hold if the design is poor. Any reasonable design will yield very similar ein at 60dB and 40db. RegardsDan LavrySent from Samsung Galaxy smartphone.
-------- Original message --------From: Mike Rivers via ProAudio <proaudio at bach.pgm.com> Date: 6/14/21  8:07 AM  (GMT-08:00) To: proaudio at bach.pgm.com Subject: Re: [ProAudio] Microphones question 
    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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