A basic skill in technical ear training is the ability to recognize the frequency reange where something notable is happening in the sound. As a simple example, when adjusting an equalizer, it can be convenient if we know "without looking" which frequency to boost or cut. These exercises are in some ways very dry and technical, but have been provided as a means of attaining very precise representations of frequencies and frequency areas. We will come back to more musical examples later. One exercise consist of determining the frequency of a sine wave oscillator, the next in determining the frequency band of filtered noise, finally we try to estimate the frequency band of a bandpass filter applied to a music signal.