Hello All, I would like to try to keep a log of sound levels in indoor home environments. I would probably want to store / transmit about 10 - 20 measures a second for hours at a time. I would like to be able to report the levels with some certainty that I am plus / minus 5 dB SPL.
I can (for now) get my hands on a very pricey high precision sound level meter for calibration. I just can't leave it sitting around in peoples houses for weeks at a time. I prefer to use RMS for averaging but would consider peak finding if someone convinced me it could be accurate. I want to use relatively cheap components and would love to have a full logging system for about $25.
I have some experience messing around with arduino, but not much about sound amplification. Last night I finally realized I would want a very large dynamic range from at least 20dB to 100dB SPL. I then thought about arduino's 10 bit ADC. So a maximum of what? about 60 dB of range? So by googling around I saw that there was such a thing as a log amplifier and then by checking ebay listings, I found the AD8307.
I read through the data sheet, but I can't seem to make out some very important considerations. It says it is demodulating - what exactly is that referring to? Is it rectifying? Should I just expect to do all the processing enveloping / RMS digitally with the microcontroller after is has gone through the A/D? Can I expect a relatively inexpensive mic and amp to get enough benefit from this. Lets say the noise floor is at some voltage that would correspond to 10dB SPL at the mic how to I make sure the transform only starts at some voltage corresponding to 20 dB SPL mic input instead of at 0 nano volts? It worries me that it is mostly used for RF in the MHZ. I hear it can handle down to DC will it be ok with audio frequencies 20 - 20K Hz? What are the negative and positive inputs for? Do I do half wave rectification on the input and then send it in to the pins? I thought "getting" the idea of how a series of limiting amplifications can lead to estimating a log transform would mean I could figure out how to make practical use of this IC. Definitely wrong.
Sorry for the eruption of questions. Feel free to answer as much as little as you would like. Thanks for your time.