At many stages of the interpretation and exploration life cycles, seismics is impacted by resolution. By definition, resolution is the ability to distinguish separate features. Improving resolution is the key problem to see thinner stratigraphic units, smaller details, lateral changes in rock properties... Whereas horizontal resolution is known to be linked to the size of the Interface Fresnel Zone, vertical resolution is usually considered as being enhanced by both high frequencies and broadband signals. This common belief comes from the fact that zero-phase signals, and particularly Ricker wavelets for which frequency and bandwidth are linearly linked, are used in seismic signal processing and modeling, as they provide easier interpretation of images, thanks to the direct link between the peaks/troughs and the reflection arrival times. Nevertheless, this belief is incorrect for mixed-phase signals (i.e., non zero-phase signals) or for signals with many oscillations. For this type of signals, we show by using the ambiguity function that, besides the bandwidth, the envelope of the signal is a fundamental tool to separate closed events and to provide reliable measurements of reflection arrival times. Bandwidth and envelope are therefore the key parameters for the analysis of seismic resolution.