Different spectrums can be tailored for signal processing schemes that want to add more noise at frequencies that need it and remove the noise with a filter whe

Different spectrums can be tailored for signal processing schemes that want to add more noise at frequencies that need it and remove the noise with a filter when it has served its purpose. For example dithering adds enough extremely high frequency noise to obliterate unwanted patterns, then applies a lowpass filter that keeps all the "good" signal and removes the noise.