  Controlling the electron dynamics in matter by individual oscillations of
light fields has recently led to the development of attosecond metrology. One
of the phenomena resulting from the nonlinear response of materials in the
strong-field interaction regime is coherent emission of high energy photons.
High harmonic spectra carry the fingerprints of sub-cycle electronic motion and
the energy structure of the studied system. Here we show that tailoring the
waveform of the driving light by using a coherent combination with its third
harmonic frequency allows to control the electron tunneling time within each
half-cycle of the fundamental wave with attosecond precision. We introduce an
experimental scheme in which we simultaneously monitor the modulation of
amplitude and emission delays of high harmonic radiation and the excited
electron population generated in crystalline silicon as a function of the
relative phase between the {\omega}-3{\omega} fields. The results reveal
unambiguously the connection between the dynamics of electron tunneling and
high harmonic generation processes in solids.
