\tikzset{
>=stealth,
thick,
block/.style={rectangle, draw=black!50, thick,
              top color=white,
              bottom color=red!50!black!20,
              font=\itshape},
op/.style={circle, draw=black!50, thick,
           top color=white,bottom color=black!20,
           font=\ttfamily},
lfo/.style={block,bottom color=orange!80},
env/.style={block,bottom color=yellow!80},
tip/.style={->,shorten >=1pt}
}
