Meters are essential because listening and looking at mixes has the same level of importance. Meters help understand clipping, as well as other unwanted sound content that is too subtle to hear during music production, especially after compression. There are many types of meters within the audio universe, being peak and VU meters the most useful ones.
It’s worth mentioning that there is a unique difference between level and amplitude. The level is considered unipolar, whereas amplitude is considered bipolar. The level is used in metering in terms of the incoming signal; this signal should not exceed the system’s limit. It doesn’t matter if the voltage is positive or negative, the most important thing is the distance from zero. The human ears are extremely sensitive, but computers have a higher sensitivity level. Because of this, digits and voltages are not that important to audio engineers.
Peak meters display the level of the signal in the exact moment the change occurs, but they do not reflect our senses. These meters are perfect for making sure a signal is not exceeding a particular limit, but they do not reflect the way the human ear perceives loudness. Peak meters provide a precise and useful reading because the decay time is much longer than the attack. Despite this, the decay tends to have less impact than the attack on the overall perception of the source’s loudness.
Average RMS/UV meters range from mechanical RC circuits that slow down the needle to studio engineered VU meters, to digital features like route mean squared (RMS). VU meters are the most popular type of meter. This type of meter exists in both software emulations, as well as in the mechanical realm. VU meters are scaled in a way that the user can see changes in moderate and loud signals, as well as in lower level increments. Phase metering is necessary because the level is a frequent variable between the left and right channels. It’s worth mentioning that a healthy mix lies between zero and one on a phase meter.