We review the impact of major effects taking place in high peak power short pulse CPA lasers, that modify the spectral amplitude and phase of a recompressed pulse and thus produce features that precede the main recompressed pulse. Especially effects associated with clipping of the spectrum, influence of the finite beam aperture on appearance of the pedestal preceding the main pulse (over the dynamic range more than 10¹⁰) as well as steepness of the leading front are considered.