How to lower microphone sensitivity

[Marius Tanasescu]

I want to measure some very loud sounds and need to reduce the input sensitivity of the mic. My audio interface is the Focusrite Scarlett. If I turn the knob all the way down to minimum, it's still not enough.
If I use Java drivers, I can surely lower the microphone gain from windows sound control. But if I want to use ASIO, that will not have any effect. Is there any way to turn down the microphone sensitivity from inside REW (when using ASIO drivers) ?

 

[John Mulcahy]

You need to make the reduction on the interface, scaling the data afterwards won't help if it has already clipped when captured. Beyond that could try measuring from further away.

 

[Antonio Di Motta]

Hi!

First you need to see what kind of microphone you have because if the sound level exceeds the dynamics of the microphone you can't do anything and the electrical signal will always be saturated and it would serve no purpose to mitigate it only to protect the sound card input.
So you need to know roughly what noise level you need to measure.
Consider that there are few microphones that have a dynamic other 130db of sound pressure some highly professional reach 140db. If you make near-field speaker measurements to minimize the effects of the environment I suggest you limit the signal to the speaker and as suggested by john slightly increase the distance between the signal source and the microphone.
If you tell me the model of the microphone, I can make some more specific considerations.

Regards
Antonio

 

[Marius Tanasescu]

It's the earthworks m23 and I'm measuring the sound pressure of a subwoofer in a car. I know this is done this a special SPL meter, but since I know It won't exceed 140 dB (but it will be somewhere near), which the microphone can handle, I'm going to use what tools I have available. I have a sound level calibrator, and after the calibration, it says that I can go for max 131 dB. If I want to go higher, I need to lower the microphone input sensitivity (which is already at minimum on my audio interface). It seems I have to use java drivers, because that way I can lower the microphone gain on the software side. Should get just as accurate results.

 

[Antonio Di Motta]

The earthworks m23 microphone has a very high sensitivity of 34mV / Pa, which means that it generates 34mV at 94db of acoustic pressure and on balance at 130db the microphone generates a signal of over 2Veff.
The Focusrite Scarlett card has a very high input sensitivity and therefore also minimal gain at those saturated sound pressures. With the hardware you have you can't solve the problem, you should use the line input that has less sensitivity but you don't have the phantom voltage to power the microphone. The solution would be to buy a Phanton power supply for the microphone and enter the line input to see if the system is within the dynamic range.

 

[Antonio Di Motta]

If even with this solution does not work you have to insert an attenuator between the output of the phantom power supply in input to the sound card in order to decrease the signal.
Of course measuring such high levels can cause serious damage to the body, we are practically at the threshold of pain, I do not recommend anyone to be exposed to these levels of acoustic pressure.

Regards
Antonio

 

[Marius Tanasescu]

I also have a presonus studio 68. Don't have it handy at the moment, but I can test it next week Think that will have a lower input sensitivity compared to the focusrite?

 

[Antonio Di Motta]

The presonus Studio 68 accepts a higher input level than the Focusrite Scarlett + 13dbu against + 9dbu from Scarlett but the 4db difference may not be enough and it would still be necessary to attenuate the microphone level.
I advise you to try, but I don't think you will solve it, 130db of acoustic pressure are difficult to manage ..