# What is a VU Meter : Circuit & Its Working

The VU meter was developed by broadcasters like NBC, CBS, and Bell Labs in the year 1939. These meters support standardize transmissions over telephone lines so-called as standard meters in the audio industry. These meters are designed to measure typical sound levels to signify the way human ears notice volume. The rise time and fall time of these meters are 300 milliseconds. The ideal audio level of this meter is approximately 0 volume unit and frequently referred to as “0dB”. These meters don’t work with fast transient sounds but work with incessant sounds. This article discusses an overview of the VU meter and its working.

## What is a VU Meter?

Definition: A VU or volume unit meter is one kind of an audio metering device. This meter is mainly designed to measure the volume of an audio signal by visually. In audio equipment, this device displays the level of a signal. So these meters are used in consumer audio devices for aesthetics and utility purposes.

VU meter working principle is, a VU meter is a simple voltmeter that uses a simple signal and displays it through 300 ms of an attack & release time. The slow attack time permits the quick transients to acquire once it registers the signal & displays its reading.

#### What is a VU Meter used for?

These meters are used for operating systems like reproduction and sound recording. To determine the signal level for avoiding overloading, distortion, and noise are used. So these meters measure power levels in audio frequency signals by using special ballistics. For complex waveforms like speech, these meters read among the values of average & peak of a complex wave.

VU meters have a dynamic characteristic that estimates the human ear response. Once a waveform of speech is applied to this meter, then the movement will specify peaks & valleys within the signal.

### VU Meter Circuit Diagram

The LED VU Meter using LM3914 and LM358 are discussed below. This circuit can be designed by using two op-amps like LM3914IC and LM358IC.

### Circuit Diagram using LM3914 IC

The circuit diagram of the VU meter using LM3914 IC is shown below. By using this circuit, the level of the signal in the audio device can be displayed like a stereo system, the audio level of CD, etc.

This circuit uses an audio amplifier to generate an analog signal to drive 10 LEDs depending on the audio signals. This circuit can be built with two modes of displays like DOT & BAR. The selection of these modes can be done by using a switch S1. In Dot mode, a single LED can be moved from top to bottom whereas, in BAR mode, all the LEDs will be turned ON serially.

The IC used in the circuit is a voltage level sensor that plays an essential role to drive all the LEDs at the output. According to the DC voltage, the LEDs will be turned ON and OFF at pin5 of the IC. This circuit operates with 9v to 12v DC however this IC also works with the voltages which range from 3v to 25v DC.

### Circuit Diagram using LM358 IC

This circuit can be built with IC LM 358. The required components of this circuit are LM358 ICs, resistors, audio jack, aux cable, variable resistor, power supply, jumper wires, LEDs.

A voltage comparator is one kind of operational amplifier and also known as an op-amp. When the voltage at the input of the non-inverting terminal is high compare with the inverting terminal, the comparator output will be high. Similarly, once the voltage at the input of the inverting terminal is high compare with the non-inverting terminal, then the comparator output will be low.

The IC LM358 is a Dual op-amp including low noise. It includes two separate voltage comparators. This is a general IC and it can be used in different modes such as summer, comparator, integrator, amplifier, differentiator, inverting & non-inverting modes, etc.

This circuit can be designed with a number of dual op-amps like the LM358 IC, where each IC includes two comparators within it. The main function of this comparator is to compare the voltage signal of audio through a reference voltage. In this meter, the adjustment of the reference voltage at the non-inverting terminal of the op-amp can be done using a voltage divider circuit. So the designing of this can be done by using resistors and a pot. Here, the resistor used at each comparator is the 1k resistor.

The main benefit of the variable resistor or potentiometer is that we don’t have to modify the resistor values in the circuit to change the reference voltage for every comparator. As an alternative, we can regulate it through a single POT.

In this circuit, the LEDs which are connected in the circuit are in reverse logic that means LEDs negative terminals are associated with the o/p of the comparators. Thus, when the output of the comparator is high, then the LED will be turned OFF. Similarly, when the output of the comparator is low then the LED will turn ON.

#### Plugin and Characteristics

By the incomparable levelness and faultless ballistic response equal the finest hardware meters. So the plugin from the Waves VU Meter will assist you to maintain suitable gain staging aimed at a pure and expansive mix.

The free plugin for VU Meter from Waves can help you to make improved mixes. We can download this free VU Meter plugin from the Waves website. This plugin is available in different formats like AU/ VST/AAX which supports Mac and PC.

The characteristics of the VU meter include the following.

• Reference level
• Rise time
• Impedance
• Frequency response

Thus, this is all about an overview of VU meter and how to build a VU meter using LM3914 IC and LM358 IC. The applications of VU meter involves where the change in audio can be observed. It can also display a slight change within the volume of the audio system. These are frequently used in sound systems and recording rooms. Here is a question for you, how to build a VU meter?