Re: [linux-audio-dev] scaling jackinput to dbSPL

--- conrad berhörster <conrad.berhoerster(a)gmx.de> wrote: Look up what voltage corresponds to 0dbFS, then given a known sensitivity figure for the microphone and a known gain for the preamp do the math. For example if 0dbFS is specified as corresponding to +22dbu (actually a voltage reference BTW), and you establish that 100dbSPL gives an output of say -50dbu from the mic, then if your preamp has a gain of say 50db, the math looks like this: 100dbSPL = -50dbu at mic, so 0dbSPL = -150dbu at mic (burried in the nose floor in all probability), the preamp has 50db gain so the output will be -100dbu at 0dbSPL. At 120dbSPL (assuming a well behaved mic and preamp), you will have +20dbu, now the Full sacle value is specified as +22dbu, so a 20dbu input will read -2dbFS , therefore in this example SPL = 122 + DBFS (always negative). This calibration obviously needs to be made for each microphone/preamp/card combination if you want decent accuracy. In practice, I would try to set up for the top of my measurement range to be about 10db or so below 0dbFS as you typically want RMS measurements and 0dbFS is a peak value and a very unforgiving place. Some of the better card manufacturers specify things like 0dbu output for -20dbFS which is obviously saying that 0DBFS = +20dbu Regards, Dan. ___________________________________________________________ The all-new Yahoo! Mail goes wherever you go - free your email address from your Internet provider. http://uk.docs.yahoo.com/nowyoucan.html