[linux-audio-user] Recording Level using Audacity and a Multiface card

[Asbjørn Sæbø]

On Sat, May 13, 2006 at 08:03:48AM +1000, D. Sen wrote:
> Yes, sure.
> 
> Here are the relevant links for the 4189 + 2671 microphone housing in 
> our setup, that connects to the Deltatron power supply.
> 
> http://www.bksv.com/pdf/Bp1380.pdf

That is a microphone, indeed.  A B&K measurement microphone, that is.  
(A note to those not familiar with B&K measurement equipment: These are 
not quite like "normal" microphones.  But they are of very high 
quality.)

According to your linke, this microphone has a sensitivity of 50mV/Pa. 


> http://www.bksv.com/pdf/bp2111.pdf

And this is the preamplifier.  (Which would, in audio, normally be 
considered part of the microphone.)

This one has, according to the link, a peak output of 7 volts, 
corresponding to an SPL of 138dB for a 50mV/Pa microphone.  Your 94dB 
signal is 44 dB below that.  Which means that the output level after the 
preamplifier will be

l = 7 * 10^(-44/20) = 0.044

And 0.044 volts is quite a bit below full scale line-level.  However, 
adding the 10x gain of your amplifier you should be at 0.44 v, which is 
certainly in the ballpark of consumer line-level.


After looking closer at it, your setup actually seems to make some 
sense.  Your amplifier (the 4416) is not one normally used for 
amplifying microphone signals, but rather accelerometers and the like.  
(As your links says: "conditioner for use with ISOTRON(R) or other 
piezoelectric voltage mode transducuers.")
But the preamplifier (the 2111) _seems_ to be of a special kind intended 
just for interfacing microphones to this kind of amplifier, so you are 
probably right in that it should work.


Asbjørn