Understanding Audio Volume Differences Despite VBR Encoding

Introduction

Despite utilizing the same Variable Bit Rate (VBR) encoding, some audio files may sound louder than others. This phenomenon can be attributed to a variety of factors, including compression techniques, dynamic range, and the presence of harmonic distortion. In this article, we will explore these factors in detail and provide insights on how to address the issue.

The Role of Compression

The largest factor that determines the perceived volume level is compression. Over the past 40 years, music has evolved in terms of perceived loudness. Advertisers and music labels realized that if their tracks sounded louder than those of competitors, they would gain more attention. This led to the so-called 'loudness wars,' a battle for sonic supremacy. However, this approach often resulted in a loss of emotion and dynamics in the music. In extreme cases, the dynamic range of some recordings was compressed to as little as a 2–3dB dynamic range, making the music tiring to listen to and devoid of the intended emotional impact. Sound engineers and musicians were often not in favor of this trend, as it was forced upon them by the stakeholders who paid for the music.

After many years of struggle, the dynamic range of most modern music has returned to a more acceptable level of around 8dB. This has been influenced by music platforms and radio stations, which demand an average Loudness Unit Full Scale (LUFS) of -14dB. At this level, it makes little sense to overcompress the music, as it will merely appear quieter or more distorted after passing through the platform's levelling processors.

Harmonic Distortion: A Multi-Faceted Issue

In addition to compression, another factor that affects volume perception is harmonic distortion. Harmonic distortion can be introduced by various means, such as the "valve" or "tube" sound or by using analog equipment that can be overdriven to a certain degree without causing unacceptable clipping.

Reflecting on my experience as a DJ in the 1970s, I recall that the compression scheme used in the recordings contributed to this issue. In the modern era, the same type of problem persists, where the files that seem loud may be compressed to fit more data into the available bandwidth, resulting in a perception of increased volume. Running these files through a modern equivalent of a Dolby playback system could restore the original bandwidth and normalize the sound. This is merely a hypothesis, but it is worth considering.

VBR Encoding and Volume Perception

It is important to note that Variable Bit Rate (VBR) encoding has nothing to do with volume. The perception of volume can be influenced by the compression level, not the bitrate. Some songs are recorded louder than others due to the widespread belief that 'loud' equates to 'better sound quality.' Unfortunately, the loudness wars still persist, and whether they continue or not is still uncertain. I have not purchased a modern album in the past ten years, given the inconsistency in recorded volumes.

Conclusion

In conclusion, the perceived volume level of audio files can vary significantly, even when using the same VBR encoding. This is mainly due to the compression techniques, dynamic range, and the presence of harmonic distortion. By understanding these factors and employing appropriate playback systems, users can enjoy a more consistent and emotionally resonant listening experience. It is also crucial for content creators to strike a balance between loudness and quality to cater to a broader audience and preserve the true essence of the music.