Fade curves

[catfact]

re : issue #4 seems like a good compromise between clickiness / record dip / pre bump @tehn give this a spin if you like

surely needs optmization maybe needs command for evaluating different values of dRec, wPre

[tehn]

getting this (build on hardware):

192.168.1.12 ~/softcut $ cmake --build build/ --target softcut
CMAKE_C_FLAGS_DEBUG is -g
CMAKE_C_FLAGS_RELEASE is -O3 -DNDEBUG
CMAKE_C_FLAGS_RELWITHDEBINFO is -O2 -g -DNDEBUG
CMAKE_C_FLAGS_MINSIZEREL is -Os -DNDEBUG
-- Configuring done
-- Generating done
-- Build files have been written to: /home/we/softcut/build
Scanning dependencies of target softcut
[  9%] Building CXX object CMakeFiles/softcut.dir/src/softcut-main.cpp.o
[ 18%] Building CXX object CMakeFiles/softcut.dir/src/SoftCut.cpp.o
[ 27%] Building CXX object CMakeFiles/softcut.dir/src/SoftCutVoice.cpp.o
[ 36%] Building CXX object CMakeFiles/softcut.dir/src/SoftCutHead.cpp.o
[ 45%] Building CXX object CMakeFiles/softcut.dir/src/SubHead.cpp.o
/home/we/softcut/src/SubHead.cpp: In member function ‘void softcut::SubHead::poke(float, float, float, int)’:
/home/we/softcut/src/SubHead.cpp:114:8: error: ‘fabsf’ is not a member of ‘std’
     if(std::fabsf(0.5f-fade_) < 0.1) {
        ^~~
/home/we/softcut/src/SubHead.cpp:114:8: note: suggested alternative:
In file included from /usr/include/c++/6/cmath:45:0,
                 from /usr/include/boost/config/no_tr1/cmath.hpp:21,
                 from /usr/include/boost/math/tools/config.hpp:19,
                 from /usr/include/boost/math/special_functions/sign.hpp:16,
                 from /home/we/softcut/src/SubHead.h:12,
                 from /home/we/softcut/src/SubHead.cpp:10:
/usr/include/arm-linux-gnueabihf/bits/mathcalls.h:181:1: note:   ‘fabsf’
 __MATHCALLX (fabs,, (_Mdouble_ __x), (__const__));

i followed the suggestion and changed fabsf to fabs and it builds (with other unrelated warnings).

this of course likely breaks the intended functionality, so i'm not sure the following is useful:

• getting sporadic digital glitching during the fade when setting rate to hard numbers like 0.47
• feeding a steady tone into a short echo gives a rather substantial pulsing effect at the loop point

anything in particular you'd like me the listen to?