[ProAudio] Microphones question

[Dan Lavry]

Excess noise is important in some cases, and it is material dependent. I 
agree that the 150 for the noise measurement can be "any: 150 Ohm.

Regarding "A weighting", I just publish both figures. In most cases it 
is 2dB difference.

Regards

Dan Lavry

On 6/14/2021 11:03 AM, Bill Whitlock via ProAudio wrote:
> Dan, I'm glad you caught that one!   Noise is a "stand alone" that 
> needs no reference except a unit of measure - and, as frequently 
> omitted by marketing types, a stated bandwidth.  And I have no problem 
> in using weighted figures as long as it's clearly stated.
>
> In my mind, the biggest barrier to understanding noise and its 
> implications is the lies, distortions, and half-truths perpetrated by 
> marketing folks!  A measurement, with test conditions and references 
> fully disclosed, is not subject to interpretation.  Sadly, many folks 
> are "educated" by such misleading information and will believe, for 
> example, that the 150 Ω resistor used for testing preamp noise must be 
> a special "low-noise" resistor.  In fact, thermal noise has no 
> dependence on the resistive material at all.  So-called "low-noise" 
> resistors are low in "excess noise" that occurs when DC current flows 
> in it - and there's a huge difference among those!  Anyone whose ever 
> heard me lecture is well aware that no love is lost between me and 
> marketing people.
>
> Bill Whitlock
>
>
> -----Original Message-----
> From: Dan Lavry via ProAudio <proaudio at bach.pgm.com>
> To: Mike Rivers <mm1100 at yahoo.com>; proaudio at bach.pgm.com
> Sent: Mon, Jun 14, 2021 9:27 am
> Subject: Re: [ProAudio] Microphones question
>
> 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.
>
> Regards
> Dan Lavry
>
>
>
>
> Sent 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 callhttp://mikeriversaudio.wordpress.com  <http://mikeriversaudio.wordpress.com/>
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