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LUFS & Level Meter

Lufs Meter

Overview

The LUFS Meter is a tool for measuring "Loudness" (the perceived volume by humans), which is the standard used in broadcasting and streaming services (YouTube, Spotify, Netflix, etc.). It uses an algorithm compliant with the international standard ITU-R BS.1770-4. It also simultaneously displays standard peak and RMS meters.

☕ Coffee Break: The "Loudness War" and the Birth of LUFS

Have you ever been watching TV and suddenly jumped because a commercial was way too loud? In the world of music CDs, there was also an era called the "Loudness War," where record companies cranked up the volume to the absolute limit just to make their songs stand out more than others.

However, if the volume varies wildly from song to song, listeners have to constantly adjust their volume knobs, which is very annoying. To solve this, a new rule was created to standardize volume not by "mechanical peak values," but by the "actual loudness perceived by human ears." That standard is LUFS (Loudness Units relative to Full Scale). Today, platforms like YouTube and Spotify use LUFS to automatically adjust (normalize) all songs so they play at a consistent, comfortable volume.

Key Indicators

LUFS (Loudness Units Full Scale)

The unit for perceived loudness.

  • Momentary (M): Instantaneous loudness (400ms window). Used for checking sharp fluctuations in level.
  • Short-term (S): Short-term loudness (3-second window). Suitable for understanding the recent loudness feel.
  • Integrated (I): The overall average loudness from the start of measurement to the present. This is the most important indicator for evaluating the volume of an entire program or track. Gating is applied to exclude silent periods.

Other Indicators

  • RMS: Root Mean Square value (electrical average level).
  • True Peak (TP / ISKb): A feature that finds "hidden peaks" unique to digital audio. It internally calculates (oversamples) to predict exactly how far the true analog sound wave shoots up between the digital sample points (the true peak). This lets you accurately know the real maximum volume the moment the sound leaves your speakers.
  • Peak (Pk): The maximum sample value of the signal.
  • Crest Factor (CF): The difference between True Peak and RMS. It represents the width of the dynamic range.

Operation

Start Metering

Begins the measurement. Graph plotting and statistical calculations will start.

Reset Functions

  • Reset Peaks: Resets the peak hold display on the level meter.
  • Reset Stats: Resets all LUFS statistical data (Integrated value, Min/Max history, etc.) and restarts calculations from zero.

Target LUFS

Sets the target loudness level. This value affects the following areas:

  • Statistics Tab: Used to calculate the difference from the Integrated LUFS (Target Offset).
  • Level Meter: The color of the Integrated bar changes based on this target value (e.g., green near the target, red when exceeding).
  • Graph Tab: The dashed reference line on the graph moves to this set value.

Show SPL

When checked, switches the units of the RMS level meter to "dB SPL" (requires prior SPL calibration in the Settings widget). LUFS values are always displayed on a dBFS basis (LUFS).

Graphs and Statistics

Statistics Tab

Provides a table of the current value (Current), minimum (Min), maximum (Max), and average (Avg) for each indicator.

  • Target Offset: Displays the difference between the set Target LUFS and the current Integrated LUFS. A "+" indicates it is louder than the target, while a "-" indicates it is quieter.

Graph Tab

Displays time-series changes in Momentary (cyan) and Short-term (yellow) loudness.

  • Dashed line: A reference line indicating the set Target LUFS.
  • Use this as a guide to check if the track or audio fits within your target loudness range.

Typical Target Levels

  • TV Broadcasting: -23 LUFS (Integrated) / -24 LKFS
  • YouTube: -14 LUFS
  • Spotify: -14 LUFS
  • CD / Club Music: -9 to -6 LUFS (Can be much higher due to the "loudness war")