The high-frequency components of the sound are mainly stationed close to the nozzle, where the dimensions of the turbulence eddies are small. Further down the jet, where the eddy size is similar to the jet diameter, is where lower frequency begins.
The high-frequency components of sound are mainly situated near the nozzle, where the turbulence eddies are relatively small in scale. Downstream, where the eddy size is similar to that of the jet itself, lower frequency begins to manifest.