From LKFS to true peak, the complete guide to Loudness

2025.07.18ㆍ by Gaudio Lab

 

What is loudness?

 

 

What exactly is loudness?

 

Loudness refers to the perceived amplitude of a sound as interpreted by human hearing. Imagine you want to tell someone about the volume of the song you're currently listening to. If the sound is loud, you'd say its loudness is high; if it's quiet, its loudness is low. However, there's no guarantee that another person will perceive loudness in the same way you do. This assurance diminishes as the number of people increases. In such cases, the most efficient method is to convey the sound's intensity using an objective, numerical metric or unit. Given the widespread need across various fields, research into loudness units has been very active. Here, we'll introduce a unit that is commonly used and highly practical in markets like broadcasting and streaming.

 

The unit we'll discuss is LKFS (Loudness K-Weighted relative to Full Scale), also known as LUFS (Loudness Unit relative to Full Scale). The parameters associated with this unit were developed by the ITU-R (International Telecommunication Union – Radiocommunication) and the EBU-R (European Broadcasting Union).

 

 

 

What factors are primarily considered when measuring loudness?

 

When measuring loudness, several key parameters are commonly used. If you examine the loudness meters provided in various measurement tools or Digital Audio Workstations (DAWs), you'll generally find that they include essential items such as Integrated, Short-Term, and Momentary loudness, True Peak, and Loudness Range. In this chapter, we will delve into the meaning of each of these parameters.

 

2-1. Key Keywords: LKFS, LU, Momentary Loudness, Short-term Loudness, Integrated Loudness, LRA, True-peak

 

  • LKFS (Loudness K-Weighted relative to Full Scale) a.k.a. LUFS (Loudness Unit relative to Full Scale)

This is one of the units for loudness. It represents the amplitude of an input signal that has passed through a K-weighting filter, which is designed to align with human hearing characteristics. You can understand the K-weighting filter as one that increases signals in frequency ranges that humans hear relatively well, and decreases signals in frequency ranges that are relatively less audible. Loudness can be categorized into Momentary, Short-term, and Integrated Loudness based on the duration over which it is measured. Momentary Loudness refers to the sound level over a 0.4-second window, Short-term Loudness over a 3-second window, and Integrated Loudness represents the overall sound level across the entire duration.

 

*What are LKFS and LUFS, and what is the difference between them?

The unit for loudness was initially conceived by the ITU (International Telecommunication Union), which defined the unit as LKFS (Loudness K-Weighted relative to Full Scale). Subsequently, the EBU (European Broadcasting Union) devised the display methods and defined terms such as Momentary, Short-term, and Integrated Loudness, along with Loudness Range (LRA), and then changed the designation to LUFS (Loudness Unit relative to Full Scale). Consequently, there is a tendency for LKFS to be used in North America, while LUFS is more prevalent in Europe.

 

 

  • LU(Loudness Unit)

While LKFS represents an absolute measured value, LU (Loudness Unit) is a relative measurement. It is used to express the difference from a reference level or to describe the range of loudness. For example, if Content A is at -12 LKFS and Content B is at -20 LKFS, one could state, "Content A sounds 8 LU louder than Content B."

 

  • Momentary Loudness

Momentary Loudness is the sound level corresponding to a 0.4-second segment of the signal after it has passed through a K-weighting filter. It is measured with a 75% overlap (0.1 seconds). This can be understood as the instantaneous sound level.

 

 

 

 

When the measurement results, as shown in the image above, are accumulated into a histogram, the result is as depicted in the image below.

 

 

 

 

 

The histogram of Momentary Loudness is subsequently used in the calculation of Integrated Loudness.

 

 

  • Short-term Loudness

Short-term Loudness refers to the sound level corresponding to a 3-second segment of the signal after it has passed through a K-weighting filter. The EBU recommends that this value be updated at a minimum interval of 0.1 seconds.

 

 

 

 

 

가우디오랩
 
The histogram of Short-term Loudness is subsequently used in the calculation of Loudness Range (LRA).
 
 
  • Integrated Loudness

Integrated Loudness is the average sound level perceived across the entire duration of a piece of content. It represents the overall loudness of the content. The calculation method is as follows:

 

Step 1) Remove the momentary loudness distribution values below -70 LKFS, then calculate the average of the remaining distribution values.

 
 
Step 2) The relative threshold is defined as 10 LU lower than the average calculated in Step 1. 
 
 

Step 3) The average of the distribution values that are above the relative threshold is the Integrated Loudness.

 
 
가우디오랩
 
  • LRA(Loudness Range)

LRA (Loudness Range) is a metric that indicates the variation in loudness over time within a single piece of content. It serves as an indicator of how widely the sound levels are distributed. The calculation method is as follows:

 

Step 1) Remove the short-term loudness distribution values below -70 LKFS, then calculate a value that is 20 LU less than the average of the remaining distribution values (this is the relative threshold).

 

Step 2) The difference between the top 5% of the distribution values and the bottom 10% of the distribution values that are above the relative threshold is the Loudness Range.

 
 
가우디오랩
 

*In both Integrated Loudness (IL) and Loudness Range (LRA) calculations, the concept of a Relative Threshold is used, but their definitions differ. For IL calculations, momentary loudness is utilized, and the relative threshold is defined as the average of the values above the absolute threshold minus 10 LU. Conversely, for LRA calculations, short-term loudness is used, and the relative threshold is defined as the average of the values above the absolute threshold minus 20 LU.

 
  • True-peak

True-peak refers to the peak value when a signal is converted to a 192 kHz sampling frequency, and its unit is dBTP. This value can be understood as a measure to prevent degradation in playback environments, particularly when using sufficiently high sampling frequencies (like 192 kHz). Since audio commonly consumed usually has sampling frequencies of 44.1 kHz or 48 kHz, upsampling is a common process. During this upsampling, the peak value can sometimes exceed the original sample peak value. An example of upsampling is provided below.

 

loudness true-peak and sample peak

 

In addition to the core upsampling technique, other processes are undertaken to prevent the signal from exceeding its representable range (attenuation), to retain only valid signals after upsampling (filtering), and to convert values to the decibel scale (logarithmization). The block diagram below illustrates the series of steps involved in calculating the true-peak when the sampling frequency is 48 kHz.

 

 

가우디오랩
 

 

2-2. Getting to know loudness

 

loudness
 
 
 
 

Why are LKFS (LUFS) used instead of the traditional RMS?

 

Previously, RMS (Root-Mean-Square) was used to measure loudness, but it did not align well with actual human auditory perception. Subsequently, the ITU and EBU developed a more sophisticated method for calculating loudness by incorporating a K-weighting filter to reflect human hearing capabilities. As seen in the loudness calculation process, this method also excludes parts that have no influence on the perception of sound pressure. It is likely that this more refined approach, compared to other units, has led to its widespread adoption.

 

 

 

What is the 'Loudness War' and why is it a problem?

 

I'd like to discuss an issue related to loudness that many of you might already be familiar with: the 'Loudness War.' To summarize it in my own words, it's when content creators produce content with the mindset of, "By making my creation louder than others, I will grab more attention from listeners. As a bonus, it might even trick listeners into thinking the sound quality is better." Alternatively, it could also be a mindset of, "While I won't make my creation significantly louder than others, I'll ensure there isn't a large difference."

While a louder sound might lead one to believe the sound quality has improved, in reality, the dynamic range narrows, reducing expressiveness, and the frequency of clipping increases, raising the probability of sound quality degradation. I hope that many consumers will recognize that excessively increasing loudness actually diminishes the quality of the audio itself, and that their consumption patterns will change accordingly.

 

loudness regulations

 

Loudness Regulations and Recommendations for Streaming Platforms  (masteringthemix)

 

 

 

Hopefully, your questions about loudness have been answered!

 

This post is a translated version of 'Loudness 101 (KR)', originally published in 2019.

 

If you're looking for more in-depth or specialized information, we highly recommend consulting the following international standard documents, which contain detailed technical information on loudness measurement and regulation:

  • ITU-R BS.1770-4: provides the standard for loudness measurement algorithms.

  • EBU-R Tech 3341, 3342: offers detailed guidelines on loudness regulation and measurement methods in broadcasting environments.

 

If you have any further questions about loudness or Gaudio Lab's loudness technologies, please feel free to contact us!

 
 
 
 
 
 
pre-image
Meet the Top AI Source Separator, Gaudio Studio as a Mobile Application

      Separate sounds in your videos and music with just a tap.   The Gaudio Studio app is finally here. Have you ever wanted to separate a specific sound while practicing an instrument or watching a video you filmed yourself?   “If only I could extract just the piano...” “If only I could hear the voice clearly, without all that background noise...”   All of that was already possible with the web version of Gaudio Studio — and now, it’s available as a mobile app. Experience our powerful AI source separation technology more conveniently, more intuitively, and more freely, right from your phone.       What makes the Gaudio Studio App different?   The answer is simple: GSEP, short for Gaudio source SEParation. It is Gaudio Lab’s proprietary AI model — one of the most advanced in the world. Thanks to GSEP, Gaudio Studio has been ranked No. 1 by Musicradar, MusicTech, and LANDR.   With this technology, you can upload an audio file and precisely separate it into individual stems — such as vocal, the drum, the bass, and the guitar — allowing for creative editing and custom combinations. And, by uploading a video, you can cleanly separate the voice from background noise, which is one of the exclusive features.        We made it easier - for our web users   “I like the web version, but using it on my phone feels a bit inconvenient…” That was the most common feedback we received from users accessing Gaudio Studio on mobile.   While many users recognized the quality of our AI sound separation on the web, using it on a smartphone browser just wasn’t ideal. It required repeated logins, reconnecting through the browser, and navigating a small screen with too many steps. While users were satisfied with the performance, the overall experience wasn’t smooth, leading many to use it once or twice and then give up.   We couldn’t stand to see our valued users struggle with inconvenience. And, that’s why we launched the app.           Web vs. Mobile, what's different?   Lighter, simpler, more accessible. That’s what the app is all about. Our mission with the app was to keep the powerful features of the web version — including GSEP-based source separation and noise reduction — while reimagining the experience for mobile with more intuitive UX. For instance, it's now much simpler to upload videos shot on your phone and remove background noise instantly.   Whether you’re a professional musician, a music major, or just someone who loves experimenting with audio, Gaudio Studio gives you studio-level control from anywhere: in bed, at a café, or on the subway — all with just a few taps. We believe professional tools shouldn’t require professional skills. That’s why we designed a touch-friendly, intuitive interface that lowers the barrier to entry and lets anyone enjoy the full power of AI sound editing.   And that’s not all — the mobile app goes even further.   Even more features: Pitch, Tempo, and Loop Control We’ve also added features that weren’t available in the web version, such as pitch shifting, tempo adjustment, and looped playback. These were some of the most requested functions from our web users. Now, you can repeat specific sections or slow them down to practice vocals or instruments with greater precision.   The first goal of the app is to help the web users use Gaudio Studio more conveniently. And of course, we’re just as excited to welcome new users discovering us for the first time through the app!             Curious about what’s next?   Following the app launch, we are closely monitoring how people use the app: Are they finding it convenient? Are they having more fun creating and practicing music? These insights will help us improve features and polish the experience. So, your feedback truly shapes what comes next!   We'll always keep our ears open and be ready to hear your valuable feedback first, and up close.       Our mission at Gaudio Lab is simple.   We provide an excellent sound experience through innovative technologies. The Gaudio Studio App is an extension of that mission. It’s a tool that helps anyone edit, remix, and enjoy music and audio — anytime, anywhere. And above all, it’s designed to make that process easy and enjoyable. We’ve built this app with care and conviction.   Now we invite you to try it for yourself — available now on the App Store and Google Play.     Here’s to your creativity and your love of sound — with more freedom, and more fun. 🎧             Would you like to know more about Gaudio Studio? GAUDIO STUDIO Source Separation Tips - A Sound Engineer's Guide  Everything about Gaudio Studio  Visit Gaudio Studio      

2025.07.04
after-image
Gaudio Lab backend engineers: The people behind the service

      The team that brings AI Audio technology to users   Turning technology into a service, and delivering it to users—today, we’re sharing the story of two developers from Gaudio Lab’s SNA (Service and Apps) squad, Paul and Johnny. Having worked closely together for years, they continue to write a new chapter at Gaudio Lab, building meaningful services powered by AI audio technology. You might not see them on the surface, but these two are the hands behind the service—where the listening experience truly begins. This is the story of two developers quietly building behind the scenes.   Q: Hi! Could you briefly introduce yourselves and tell us about your roles on the SNA squad?   Paul: Hi, I’m Paul, a backend engineer on the SNA squad. I work on building web-based services that deliver Gaudio Lab’s AI audio technology to end users. Right now, I’m developing a product called Gaudio Developers, which is a different version of Gaudio Studio. It allows customers to explore and apply our latest audio technology through OpenAPI.   Paul and his kids at Hey MA&PA Event       Johnny: I’m a DevOps and platform engineer. Simply put, I make sure the programs built by developers are delivered to users smoothly by automating the middle layers and improving efficiency. I also work on improving our internal development environment and culture so our team can work more effectively. These days, I’m working with Paul on Gaudio Developers, and I also help operate Gaudio Sing.         What makes working at Gaudio Lab special   Q: What was your first impression of Gaudio Lab? Compared to your previous workplaces, how is the team culture or way of working different?   Paul: The biggest difference is that we’re empowered to take ownership of our work. Within the resources we’re given, we have the flexibility to manage our schedules and participate directly in everything from system design to decision-making. Because of that, I feel more attached to the projects I work on and more driven to see them through to the end.   Johnny: In my previous companies, failure just wasn’t an option. The focus was so heavily on results that people became more conservative when choosing technologies or building new features. It was often like, “This method worked before—why change it? Let’s just do it the usual way.” But at Gaudio Lab, it’s different. If you have a solid reason, people are open to new ideas. Even if something fails, our leader will say, “That’s OK. The decision was mine—that’s not on you.” Instead of blaming, we reflect and learn together, and that opens the door to better results.     Q: SNA seems like one of the most communicative teams. How do you usually work through problems and collaborate?   Johnny: Communication is absolutely critical. If we misunderstand directions or lack clarity on goals, the entire development can veer off course. And once something goes live, fixing it takes even more time and effort. To avoid that, we actively ask questions and discuss openly—until we’re all sure we’re heading in the same direction. We often say things like, “I’m not sure this is the right direction.” “Can I ask why you think this approach works?” “Is there another way we could look at this?” These kinds of conversations help us share diverse perspectives and avoid being stuck in a single mindset.   Paul: When a problem arises, the person responsible will first take the lead in solving it. But if things get tricky, the whole team jumps in to help. Our team lead, Min, is always there to guide and support us when needed—which is really reassuring. We mostly use Slack for async communication, and we have short daily standups to share progress. It’s a very open environment where anyone can ask for help or suggest a new idea anytime. That mutual trust really allows us to work independently, yet stay connected as a team.     Q: With such smooth collaboration, it sounds like you have a lot of respect for your teammates. What are they like?   Johnny: Min is a fantastic team lead. He gives clear direction and removes obstacles so we can focus on building. Paul is someone I trust completely. He’s always approachable and reliable—someone I can count on without hesitation. 😎 And our juniors, Handy and Hazel, are growing incredibly fast. I’m genuinely excited for what’s ahead for them. Paul: I totally agree with Johnny. Every person on our team carries a strong sense of ownership—like, “if I don’t do this, no one else will.” That level of commitment is what makes the team work. Gaudins often say "The best part of working here is the people."—and I think our team is a perfect example of that.       Grow without limits   Q: You’ve both been with Gaudio Lab for 4–5 years now. What’s one project that stands out most during your time here?     Paul: The most memorable for me is the GTS (AI Text Sync) project I worked on right after joining. Back then, we didn’t have any web-based services, and I was the only developer on it—so I had to build everything from scratch. I designed and implemented the entire system architecture based on Docker, including OpenAPI, licensing, and the admin web service. At my previous jobs, roles were more segmented, so I’d only contribute to one part. But here, I handled everything from planning and development to deployment and customer support. There was a lot I didn’t know, so I dove deep—watching tutorials, reading books, and just immersing myself. It was tough, but a deeply meaningful experience for me.   Johnny: For me, it’s Gaudio Studio. Before this, I mostly worked on B2B products targeting enterprise clients. Gaudio Studio was the first time I worked on a service designed for direct consumers. Consumer audiences are much more diverse—not just in scale but in behavior, expectations, and how they give feedback. That meant their needs were more varied, too. So I found myself thinking things like, “Would this make the user happier?” and taking a more proactive role in shaping the direction of the service. I really enjoyed that process—it challenged me and made the work exciting. 😊     Q: Those periods of deep focus clearly shaped your growth. Where do you see yourself heading as a developer?   Paul: Lately, I’ve been actively using AI tools to boost my productivity. I’ve automated repetitive tasks and found faster, more effective ways to troubleshoot issues. That’s helped me grow not just technically, but also in how I approach work overall. Looking ahead, I want to combine AI tools with backend systems to create more efficient architectures—ones that deliver maximum impact with minimal resources. Ultimately, I want to build systems that are not only technically solid, but also deliver great user experiences. Johnny: I want to be what I call a “borderless engineer.” Instead of thinking, “I’m a developer, so I only write code,” I want to cross boundaries when it makes the product better. Whether it’s ops or planning, I want to be part of the problem-solving process—wherever development and real-world needs intersect. That’s how I want to grow: by contributing beyond my job title.         We value passion and collaboration   Q: Lastly, any words for future Gaudins?   Paul: If you’ve ever wanted to turn an idea or technology into a real service, this is the place to do it. At Gaudio Lab, you get to experience the full cycle—from concept to execution. If you’re looking to grow in a tight-knit, high-trust team, there’s a lot to gain here. I hope we get the chance to work together and create meaningful value through audio technology. If you’re someone who takes initiative and learns through action—you’ll be more than welcome here. And yes—it's totally okay to fail! 🙌🏻   Johnny: For us, what really matters is sincerity. We actually read every blog post on your resume. We review the code. We care. Having lots of experience is great, but what’s more important is whether you put your heart into that experience. If you’re ready to grow together and care deeply about what you build, we’d love to have you on this journey with us.       If you found the story of the GDK development team intriguing, Explore Life at Gaudio Lab:)    

2025.08.07