Thank alots for the help.

 
Since there's a package.txt file with it, the external is meant to be compiled with the flext build system.
You can have a look at the flext readme.txt or build.txt files.
It boils down to the following:

sh path_to_flext/build.sh pd gcc
sudo sh path_to_flext/build.sh pd gcc install


I still have an error on ubuntu g++ 4.4.3 :
--------------------------------------
sh /home/marco/pd-flext/flext/build.sh pd gcc

make -f /home/marco/pd-flext/flext/buildsys/gnumake-sub.mak  PLATFORM=lnx RTSYS=pd COMPILER=gcc BUILDPATH=/home/marco/pd-flext/flext/buildsys/ PKGINFO=package.txt BUILDCLASS=ext TARGETMODE=release TARGETTYPE=single _build_
make[1]: Entering directory `/home/marco/sms_peaks'
mkdir -p pd-linux/release-single
mkdir -p pd-linux/release-single/
g++ -c  -msse -mfpmath=sse -ffast-math -O3  -pthread -fPIC -fvisibility-inlines-hidden -DNDEBUG -DFLEXT_SYS=2 -DPD -I/home/marco/puredata-0.42.5/src -I/usr/include/stk -I/usr/include/sndobj -I/usr/include/flext main.cpp -o pd-linux/release-single/main.opp
main.cpp: In member function ‘virtual void<unnamed>::sms_peaks::CbSignal()’:
main.cpp:98: error: cannot convert ‘flext_single::buffer::Element*’ to ‘t_sample*’ in initialization
make[1]: *** [pd-linux/release-single/main.opp] Error 1
make[1]: Leaving directory `/home/marco/sms_peaks'
make: *** [build-release-single] Error 2
---------------------------------------------------------

If you have this patch compiled for osx, Please can you put it online?

I have both osx and linux here ;)

Thanks for help!