The audio level: this is how the "level" works with sound signals

Speaker level, line level, and microphone level: connect audio devices correctly

What is a "level" in the field of audio? This article focuses on three important audio levels: speaker level, line level, and microphone level. Each of these levels plays a crucial role in audio technology. A thorough understanding of the various audio levels is essential for expert planners to ensure correct signal processing, appropriate gain and distortion-free sound. By knowing the respective levels, expert planners can select the right components and achieve optimal sound quality.

The difference between absolute level and relative level

In the audio world, it is important to understand the difference between absolute level and relative level. These concepts play a significant role in the correct handling of audio levels.

Absolute level

Absolute level refers to the actual level of an audio signal in relation to a specified reference (this makes it absolute, i.e. non-relative). It is measured in decibels (dB) and indicates how strong the audio signal is. Absolute levels are indicated by appending letters to the dB. 10 dB is by definition a relative indication, while '+6 dBu' is an absolute level indication related to the voltage value that was agreed for 0 dBu.

Absolute level is often used to determine the output level of an audio signal, such as the level of a microphone signal, an amplifier or a speaker. The absolute level is a fixed value and independent of other signals or components.

Relative level

In general, each level specification is a relative value unless it is explicitly stated as an absolute level. In contrast to the absolute level, relative level refers to the relationship between various audio signals or components. It is often used to describe the relationship between different channels, tracks, or devices. Relative level is usually measured in decibels (dB) and represents how loud or quiet one signal is compared to another. It is used to adjust the balance between the different audio channels or for the level control of an audio signal in relation to a specific reference level.

Applications in audio planning and installation:

When planning and installing audio systems, you must ensure that the absolute levels of the various components such as microphones, amplifiers and speakers are appropriately balanced to ensure good sound quality and adequate volume. At the same time, it is important to properly harmonise the relative levels between channels and components to achieve balanced sound reproduction and avoid unwanted level fluctuations.

Tool: level meters

To measure and set both the absolute level and the relative level, level meters are indispensable tools. Level meters display current levels in decibels, allowing audio professionals to take accurate measurements and adjust levels accordingly. When working with relative levels, level meters can help to achieve the right balance between channels or the desired level control.

For simplification: levels in volts

Because we want to avoid making this article epic in length, we will simplify for better understanding: we will indicate the various audio levels in volts. In this context, if you want to delve deeper, it is important to understand how decibels work.

The conversion from level (dBu) to voltage (volt) is U = 0.775 x 10^(L/20).


Speaker level

A speaker must enable movement of the cone so that it can generate sound waves that we then hear. For this purpose, it needs an electrical signal. Smaller speakers only require a few volts. Larger speakers often need at least 60 volts to generate a loud sound.

Line level

A speaker is connected to an amplifier - either externally or as part of one active speaker. With a HiFi amplifier, we have many devices that are in turn connected to it, usually via a line-in jack: CD or DVD players, cameras (if we want to reproduce sound), radios. The line-in jack and the line-out jack all have so-called "line levels". This line level is about 0.5 volt to 1 volt. It is the task of the amplifier to amplify the half to one volt of line level to 10 or more volts of speaker level.

Microphone level

So the initial situation so far is: 0.5 to 1 volt line level going into the amplifier. The line level is brought to speaker level by the amplifier (i.e. significantly increased). How does the microphone relate to this? The output voltage of a microphone is very low: from 1 mV all the way up to 100 mV in some cases, in other words: 1/1000 to 1/10 of a volt. This means: with such a tiny amount of power, even a classic amplifier does not help enough to produce a clearly audible sound. That's why it needs a microphone preamplifier.

Digital level: dBFS

The dBFS (Decibels relative to full scale) is a digital level measurement unit that indicates the maximum power or level of a digital signal. The reference point for the dBFS is at the maximum control level, i.e. at 0 dBFS. A level above 0 dBFS results in clipping and unwanted distortion.

Decibel and dBFS

Similar to other level measurements, dBFS is measured on a logarithmic scale. An increase of 3 dBFS corresponds to a doubling of the power. Negative dBFS values indicate a lower level than the maximum reference level. For example, -20 dBFS corresponds to a level that is 20 decibels below the maximum level.

Using dBFS

The dBFS is mainly used in digital audio production, in mixing and mastering as well as in the transmission of digital audio signals. Digital audio interfaces such as AES/EBU or S/PDIF, use dBFS to ensure that the signal is transmitted and processed correctly. Most digital audio devices and software workstations also work with dBFS.

Level control reserve and headroom

In contrast to analogue audio signals, where a certain amount of clipping may be acceptable, with digital signals it is particularly important to have enough headroom. Headroom refers to the margin between the maximum level (0 dBFS) and the actual level of the audio signal. By providing sufficient headroom, unwanted distortion and clipping can be avoided.

Level control in digital systems

A lot of digital audio equipment and software workstations have level meters that display the dBFS value. This enables audio professionals to ensure the signal is not clipping or too low for optimal sound quality.

How do we bring different audio levels together?

There are several tools for this, some of which we describe below as examples.

Microphone preamplifier

In order to raise the level to one sufficient for the amplifier, a small microphone amplifier is required. The raises the audio level from microphone levels to line level. A microphone preamplifier between the microphone and a normal amplifier boosts a microphone's millivolt voltage to line level. Microphone preamplifiers are often built into devices that are designed to be connected to a microphone.

Do not connect a line level to a pure microphone input, because the input "expects" only the low voltage level of a microphone.

Attenuators, also called "level converters" or DI boxes

We can attenuate the signal with attenuators - similar to the way an amplifier increases the signal, an attenuator weakens the signal. With attenuators, however, you can feed the line level directly into the microphone input, which is why these devices are also called direct input boxes or DI boxes.

Three important points when working with different levels
  1. A microphone level input is usually provided with an XLR jack. A line level input, however, is typically provided using an RCA jack, 6.35 or 3.5 mm jack plug.

  2. Please do not assume that the levels correspond just because the connections are identical. The inputs are usually marked with an indication of the respective level.

  3. Note that different wireless receivers have different output levels. Therefore, you should always refer to the instruction manual for the radio receiver used to check the output level.

Dynamic compression and limiter to control the dynamic range

The dynamic range of an audio signal refers to the difference between the quietest and loudest parts of the signal. Dynamic compression is a tool that is often used to control the dynamic range of an audio signal. It enables targeted alignment of the level differences by attenuating loud sections and amplifying quiet ones. Limiters are a special form of dynamic compression used to ensure that the level does not exceed the maximum level control range.

Conclusion: there are three important signal levels to consider

  1. Microphone level (in millivolt range)

  2. Line level (approximately 1 volt)

  3. Speaker level (10 volts or more)

Different levels that do not align are the most common cause of audio distortion.

Another important but often misunderstood unit with regard to audio level is the decibel.

Headergraphik: Adobe Stock / belamy

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