Another component of sound is the sound quality. This is related to how people perceive a sound, as in whether one finds it soothing or annoying. The perception of sound quality is affected by the pitch, tone, and modulation of the sound. The pitch varies with the frequency of the sound wave. A high frequency wave will result in a high pitch, and vice versa. The tone is a steady periodic sound generated from a sine wave, and there are some tones that are more discernable to humans than others. Modulation from a fan is best described as the pulsating sound from the spinning of the impeller. Sound quality can be measured and quantified by the test setup shown here, utilizing an ISO10302 plenum box and a Binaural Head recorder.