Large-scale direct numerical simulations of temporally developing turbulent mixing layers, as models for the near-nozzle shear layers of high-speeds jets, are used to examine the generation of the intense 'crackle' sound they produce. The simulations are confirmed to reproduce the well-known shock-wave-like pressure fields and peculiar pressure skewness observed for such flows. It is also confirmed that these observations are insensitive to Reynolds number. The role of the specific large-scale structure of the turbulence is investigated by a novel modification of it, motivated by the known instabilities of high-versus low-speed free shear flows. It is concluded that the structure of the turbulence has little affect on Sk.