In nonlinear propagation, evolution of an acoustic pressure waveform depends strongly on the characteristics of the waveform. For example, the commonly observed waveform steepening is a coherent process involving a specific phase relationship between spectral components. Highamplitude military jet noise may show peak pressures ten times the root-mean-square pressure and may include jumps of hundreds of pascals in a few microseconds or less. Measurement of these waveforms containing fast rise times requires large bandwidth and high fidelity in phase. If the bandwidth and phase are not preserved then the waveforms can lose precisely those features that distinguish them from linear propagation. Whether such waveforms are used as starting fields for nonlinear propagation codes or as measurements for code validation, the impact of limitations in the measurement system must be understood.