VU stands for volume units—and VU meters are tools that display an average signal level, as they allow the user to perceive louder sounds. VU meters have a moving needle on a graduate scale. The upper part of the scale is calibrated in dB, and the lower one in percentages. Volume is quite subjective since one listener can consider that a sound is loud while another might not feel the same way. For this reason, VU meters provide an objective electronic reading of volume. They are essential within the audio production universe.
VU Meters: All About Simplicity
A Brief Snippet of History
The first known VU meter sprung in North America. Its name was SVI, short for Standard Volume Indicator. The name comes from the meter scale, which was originally calibrated in volume units. Even today, one of the simplest audio meter designs is the SVI/VU meter, as it acts as a simple voltmeter with a moderate attack time of roughly 300ms.
VU Meters: How They Work
The amplitude and the duration of the signal influence the VU display. When the sine-wave signal is stable, the VU meter can give an accurate reading of the RMS signal voltage. Furthermore, when using more complex speech o musical signals, the VU meter tends to under-read the continuous sound. Even though these signals usually have the same peak voltage, the continuous sound will be considerably higher than that of the transient signal. Almost all VU meters respond to both the positive and the negative parts of the input audio signal, although some models are only capable of measuring one part of the waveform. When this happens, asymmetrical signals emerge.
A Blindspot: Accuracy
VU meters might not be very accurate, especially today. They can’t always identify unexpected, sharp, or short increases of a sound signal. Also, many are not able to determine an average volume level. In addition, they tend to ignore some of the sound bursts that appear. Similarly, they tend to overreact to the flow frequency part of a sound.
In contrast, today, a very precise metering system is the ITU-R BS 1770. This system is better than the VU meter because it offers an innovative Loudness Meter scaled in LUFS, along with an oversampled True Peak Meter scaled in dBTP.
