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Phil Allison[_4_] Phil Allison[_4_] is offline
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Default Comparing two audio interace mice pre's for self noise.

wrote:

--------------------------

Preamps often have 1/F noise not white noise so the majority of
the noise power you will read on a flat meter will be low freq,
which will not always be audible.



** Not true a tall.

I measure preamp noise using a 20Hz to 16kHz, 12dB/oct band pass filter to remove the HIGH frequencies that would add many dBs to the reading.

With a 200ohms load resistirm the nosie is very much WHITE !



A better measure of how noisy it _sounds_ would be to use A or some other weighting to make the measurement.


** A weighting only reduces the reading by maybe 6dB.

Cos the energy is all concentrated at the HIGH end of the range.

Equal amount between 8kHz and 16kHz as for the rest.


But it is also true, most eletret mics effectively have a built in preamp


** Only "most" ??

so I would also do a test with the actual mic you want to use as well as with the terminator.



** Then you are testing the mic and need a TOTALLY silent room.

The folk at Rode use a "silent chamber" - a cast iron sphere the mic goes inside via an air tight door. The room needs to be quiet too to get reliable readings.


...... Phil


..... Phil