Hi,
I have a project in which I need to control some LEDs using the amplitude of a wav file. I have the Arduino side of things down, however I'm not sure how to measure the amplitude of a sound file in PD. Can anyone help with this piece? Reference to objects, etc?

[env~] sounds like what you're looking for.
look at [soundfiler] for how to load/play soundfiles, usually read it to a table and then play it from the table.
you might need to scale the output of [env~] a bit, in my experience it only gave values between about 70-100 when there was a strong single, lower than 60 you're looking at ambient noise (for the most part, again in my experiences so your mileage may vary).
the help patches/tutorial patches on playback should help you out too, some help/tutorial patches can be confusing but the playback stuff is stuff you need to learn early on so it's laid out decently in the docs.
hope this helps some, i'm glad to help on any followup questions. although i've never used an arduino yet so on that side of things i'm no help.
cheers - slv

hey, thanks so much for the help.
what's a good reference for looking up the description and attributes of objects, messages, etc?

hi...good day/....
have fun??...