Determining Microphone (Self Noise)

[Zack]

I came across these notes from Rane's web site that helped explain how to determine correct matching of pre-amps with microphones.  I was mostly interested in the section of how to figure a microphones self noise and decided to check my own mics to the scale.  The scale seemed to be fairly accurate as I found my 4073a to fall exactly where the mic's spec sheet listed.... a pretty noisy mic (high output) compared to others.  I then looked up the specs for a MK41 capsule and entered it into the scale and those results made sense to me (very low self noise).  Lastly, I did the same for a MK012 using a hyper-cardoid capsule and found (according to the scale) it's self noise to be nearly the same as the Schoeps.... yet my ears tell me differently.  Is it possible the specs listed for the Oktava are incorrect?

Well, I just thought this was a bit interesting... I like to go out to different locations and record ambient sfx for my library and using low self noise instruments is always key.  I've always found my Oktava's to be a bit noisy and no where near a Schopes regardless of what this chart is telling me however.

RANE'S SELF-NOISE CHART

[studiomprd]

"  Is it possible the specs listed for the Oktava are incorrect? "

well, yes, but there is more to consider...

you might have noticed that Schoeps mic's are a lot more expensive than Oktava's...

there are reasons!  ...good reasons!!

there is a rule: generally speaking, you get what you pay for.

just some things included are consistancy and QC.

and BTW, there are numerous variations in Oktava's that are available out there, including counterfeits...

then there is methodology: "  how to figure a microphones self noise and decided to check my own mics to the scale. I then looked up the specs for a MK41 capsule and entered it into the scale "

you cannot make measurements like this, they requires proper test equipment and procedures.

[Zack]

" Is it possible the specs listed for the Oktava are incorrect? "

well, yes, but there is more to consider...

you might have noticed that Schoeps mic's are a lot more expensive than Oktava's...

there are reasons!  ...good reasons!!

there is a rule: generally speaking, you get what you pay for.

just some things included are consistancy and QC.

and BTW, there are numerous variations in Oktava's that are available out there, including counterfeits...

then there is methodology: " how to figure a microphones self noise and decided to check my own mics to the scale. I then looked up the specs for a MK41 capsule and entered it into the scale "

you cannot make measurements like this, they requires proper test equipment and procedures.

Oh trust me, I'm well aware of the differences between them.. and that's what threw up a flag after reading this article.  I realize this chart is probably not decimal accurate, but if I could gauge the ballpark of what to expect from a device would be very helpful.

[paulj]

Zack,

it's self noise to be nearly the same as the Schoeps.... yet my ears tell me differently.  Is it possible the specs listed for the Oktava are incorrect?

The Rane chart (table 3) gives the output noise of the mic based on sensitivity and self-noise specs.  The noise output  is calculated in the same units as the EIN spec given for preamps and is directly comparable.  What the chart allows you to do is determine if a preamp's noise floor will degrade the microphone noise floor. 

The AT4073a (70.8mv/Pa sensitivity and 14dB self-noise) has an output noise of -101dB(A), so using Rane's guidelines a preamp with EIN (equivalent input noise) of between -107 to -111dB(A) should be sufficiently quiet to prevent degradation of the mic's noise floor.  The MK012 (10mv/Pa sensitivity and 18db(A) self-noise) will have output noise of -114dB(A) and would require a preamp with EIN of -120 to -124dB(A) to prevent the preamp degrading the mic noise floor.  The Schoeps MK41 (14mv/Pa sensitivity and 15dB(A) self-noise) has an output noise of -114dB(A) which is the same as the Oktava as you mentioned. This doesn't mean the self noise is the same just the output noise is at the same level - the MK41 is still has a noise floor 3dB lower than the Oktava.

As an example if you compare the output noise with the EIN specs for a SD302 mixer -- -127db(A) -- you can immediately see that preamps will not degrade the noise floor of any of the above microphones.

cheers

Paul