In article ,
bluesjeon wrote:
the recording format is "24bit 48 khz wav"

Sure, but is there 24-bit data in that 24-bit file?

when u record silence in protool with the input is not connected
what is the peak value?

That depends on the converters. If you record without any converters at
all, the peak value should be 0x0000.

I am using Apogee ad-converter and get -139db in some recording program
but in other recording program the results is not the same

Right, because you are looking at different word length in the different
programs.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."