We often think of sound in simplistic terms: it's either loud or soft. However, the world of audio engineering introduces a more nuanced concept, "perceived loudness." This principle shapes how we experience music, radio broadcasts, and virtually any other form of audio media. This blog post will delve into the fascinating concept of perceived loudness, explaining what it is, why it matters, and how it's managed in audio production.
What is Perceived Loudness?
Perceived loudness refers to how loud a sound appears to the human ear, which doesn't always correlate directly with its actual, or physical, loudness measured in decibels (dB). Several factors can influence perceived loudness, including the frequency and duration of a sound.
For instance, humans are more sensitive to frequencies between 2,000 and 5,000 Hz, the range where the human voice resides, so these sounds might seem louder to us, even at the same decibel level as sounds at other frequencies.
Sounds that maintain at a high decibel level also tend to appear louder than sounds that abruptly peak at the same level. For example, a synth sustaining at 85 dB will likely sound louder than a snare drum that momentarily peaks at 85 dB.
The Importance of Perceived Loudness
Perceived loudness plays a crucial role in audio production across various fields, from music and radio to film and television.
Imagine listening to a song where the vocals are drowned out by the drums or where the guitar solo suddenly seems jarringly loud. Inconsistent perceived loudness can lead to a disjointed and unpleasant listening experience. That's why audio engineers work meticulously to balance the perceived loudness of different elements in a track, ensuring a smooth and engaging listening experience.
Similarly, in broadcasting, perceived loudness is vital to maintaining a consistent listening experience. If one show is significantly louder than another, listeners might have to keep adjusting their volume levels, leading to a frustrating experience. Therefore, broadcasters adhere to specific loudness standards, such as the EBU R128 standard in Europe or the ATSC A/85 standard in the US, to ensure consistency.
EBU R128 and ATSC A/85 are standards developed to maintain consistency in audio loudness across different broadcasts. These standards were developed in response to complaints from audiences about significant and jarring differences in volume between different television programs and commercials.
EBU R128
The EBU R128 standard was developed by the European Broadcasting Union (EBU). It provides guidelines for measuring and normalizing audio loudness in broadcast audio. The standard is based on the concept of loudness units relative to full scale (LUFS), a measure of perceived loudness over time.
The EBU R128 standard specifies that audio should be normalized to -23 LUFS, with a maximum true peak level of -1 dBTP. This aims to ensure that the volume of all broadcasts is consistent, and that there are no sudden changes in volume when switching between channels or programs.
ATSC A/85
The ATSC A/85 standard was developed by the Advanced Television Systems Committee (ATSC) in the United States. Like the EBU R128 standard, it provides guidelines for maintaining consistent loudness in broadcast audio.
ATSC A/85 is based on the same principles as EBU R128 and also uses LUFS as its measure of loudness. However, the ATSC A/85 standard specifies a slightly different target loudness: -24 LUFS. The maximum true peak level is the same as the EBU standard, at -1 dBTP.
Both of these standards not only improve the listener's experience by ensuring consistent loudness but also prevent potential damage to audio equipment caused by sudden changes in volume. They are now widely used in broadcasting and have also been adopted by streaming services.
Managing Perceived Loudness
The tools of the trade for managing perceived loudness are common audio processors like equalizers (EQs), compressors, and limiters.
Equalization allows audio engineers to adjust the balance of different frequencies in a sound. Since our perception of loudness is influenced by frequency, EQ plugins can be used to make certain elements of a track seem louder or softer without changing their peak volume level.
Compression reduces the dynamic range of a track—the difference between the loudest and quietest parts—making loud sounds quieter. Indirectly, you can then make quiet sounds louder by turning up the level of the entire track; this is due to the increased headroom that's been provided by the compression applied. Compression can help to create a more consistent perceived loudness throughout a track.
Limiting, a more extreme form of compression, prevents an audio signal from exceeding a certain level. This prevents audio tracks from becoming uncomfortably loud. Although, the overuse of limiter plugins can lead to a phenomenon where the dynamics of a track are lost, track elements feel less punchy and powerful, and the ears of listeners become quickly fatigued.
The Future of Perceived Loudness
As audio technology continues to evolve, so do the tools and techniques for managing perceived loudness. New standards are being developed to provide better consistency across different platforms and devices. Streaming platforms like Spotify, Apple Music, and YouTube now use loudness normalization, which automatically adjusts the volume of different tracks to a consistent perceived loudness level.
Meanwhile, audio software companies are developing more sophisticated plugins and algorithms to manage perceived loudness more effectively. AI-powered tools can now analyze and adjust the perceived loudness of audio files, making it easier than ever for producers to create high-quality, balanced audio. Mastering tools like iZotope's Loudness Control module a part of Ozone 10 let you monitor and adjust loudness, whereas mastering DAWs like WaveLab Pro have a loudness normalization feature built-in.
Understanding and managing perceived loudness is vital to creating a consistent, high-quality listening experience. While it might seem like a niche concern, perceived loudness management subtly influences your interaction with audio content every day. Whether you're listening to a chart-topping hit, binge-watching a Netflix series, or tuning into your favorite podcast, the careful management of perceived loudness shapes your experience.
With the advent of new technology and audio engineering tools, the capability to control and manipulate perceived loudness is becoming more accessible. As we continue to consume audio content across a variety of platforms, the demand for balanced, well-produced audio will only increase.
In short, perceived loudness is more than just a technical audio engineering term; it's a fundamental aspect of how we experience sound. It ensures that our listening experiences, whether in music, television, or film, are consistent, harmonious, and pleasing. Listeners might not always notice when perceived loudness is well-managed, but they'll definitely notice when it's not.
