All our customers have one thing in common : they want a smooth, consistent musical experience, without sudden random jumps or dives in perceived loudness. Tracks should all feel like they have the same loudness, regardless of their origin.
Technically, the process of making sure all tracks play at the same loudness is called Loudness Normalisation. And while it may seem mundane, it is actually a hard engineering problem.
To address this, SPECTRE implements the ITU-R BS.1770 (formerly known as EBU R128) algorithm. As of the time of writing this article, it is the industry-wide gold standard for loudness measurement and normalisation. It is implemented by Apple, Spotify, Tidal, Netflix, Sony, and countless TV and radio broadcasters.
This algorithm however, is not a silver bullet. There are certain circumstances under which normalised tracks may still sound too loud or too quiet.
These are the corner cases which might lead to loudness fluctuations :
Speaker quality
A speaker is deemed "full-range" when it can deliver music across the complete range of frequencies audible by a human ear (i.e. 20Hz-20kHz). Most "high-fidelity" speakers are classified as "full range". However, it is common for speaker systems unintended for music as a primary use case — such as Public Announcement speakers, or Fire/Safety speakers — to struggle with this. For such speakers, it is typical to find deep bass, or top high frequencies either attenuated or missing entirely. When that happens, the missing frequencies will lead to an overall diminished perceived loudness.
Bass-heavy tracks, and treble-heavy tracks
Some tracks make heavy use of lower frequencies (i.e. bass), or higher frequencies (i.e. treble). In such cases, if played over speakers which are not "full-range", the track will feel quieter than other, more balanced tracks.
Our Art Directors actively attempt to avoid such tracks but, depending on how narrow the creative brief is, we might sometimes be obligated to use such tracks.
Other factors
Other less likely possible factors can include :
Uncorrected room acoustics: bad room acoustics can lead to some frequency ranges feeling louder/quieter than others. This can lead to perceived loudness fluctuations between tracks.
Improper equalization: improper equalization can lead to some frequency ranges feeling louder/quieter than others. This can lead to perceived loudness fluctuations between tracks.