[ProAudio] Microphones question

Mon Jun 14 12:11:05 PDT 2021

The microphone measurement standard recommends the use of A-weighted rms 
noise specifications in addition to ITU-R BS.468-4, which specifies not 
only a frequency weighting curve but a quasi-peak detector which 
penalizes for low frequency pops and clicks, which can be a factor for 
some poorly executed microphone designs.

Yes, even some of the experts in the standards world talk about "low 
noise" resistors. We have to pick our battles.

On 6/14/2021 12:01 PM, Dan Lavry via ProAudio wrote:
> 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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