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.
In the context of a jet, high-frequency sound components tend to be concentrated near the nozzle, where the turbulent eddies have smaller scales. As one progresses along the jet, where the eddy sizes approach the diameter of the jet, lower frequency components start to become more pronounced.