Consider the following scenario:
Two copies of an audio file. File 1 is Stereo, Loudness Normalized to -16.0 LUFS. File 2 is Mono, also Loudness Normalized to -16.0 LUFS.
Passing both files through a Loudness Meter confirms equal numerical Program Loudness. However the numbers do not reflect an obvious perceptual difference during playback. In fact the Mono file is perceptuallylouder than it’s Stereo counterpart.
Why would the channel configuration affect perceptual loudness of these equally measured files?
I’m going to refer to a feature that I came across in a Mackie Mixer User Manual. Mackie makes reference to the “Constant Loudness” principle used in their mixers, specifically when panning Mono channels.
On a mixer, hard-panning a Mono channel left or right results in equal apparent loudness (perceived loudness). It would then make sense to assume that if the channel was panned center, the output level would be hotter due to the combined or “mixed” level of the channel. In order to maintain consistent apparent loudness, Mackie attenuates center panned Mono channels by about 3 dB.
We can now apply this concept to the DAW …
A Mono file played back through two speakers (channels) in a DAW would be the same as passing audio through a Mono analog mixer channel panned center. In this scenario, the analog mixer (that adheres to the Constant Loudness principle) would attenuate the output by 3dB.
In order to maintain equal perception between Loudness Normalized Stereo and Mono files targeting -16.0 LUFS, we can simulate the Constant Loudness principle in the DAW by attenuating Mono files by 3 LU. This compensation would shift the targeted Program Loudness for Mono files to -19.0 LUFS.
To summarize, if you plan to Loudness Normalize to the recommend targets for internet/mobile, and Podcast distribution … Stereo files should target -16.0 LUFS Program Loudness and Mono files should target -19.0 LUFS Program Loudness.
Note that In my discussions with leading experts in the space, it has come to my attention that this approach may not be sustainable. Many pros feel it is the responsibility of the playback device and/or delivery system to apply the necessary compensation. If this support is implemented, the perceived loudness of -16.0 LUFS Mono will be equal to -16.0 LUFS Stereo. There would be no need to apply manual compensation.
Julian Ludwig é diretor do Pro Áudio Clube, produtora de áudio Jacarandá, Loc On Demand e Jacarandá Licensing. Trabalhou para empresas como: Guaraná Antartica, TV Gazeta, NET, Chivas Regal, FNAC, Prefeitura de São Paulo, Mukeca Filmes, Agência LEW’LARA TBWA, Agencia MPM, Agência Content House entre outras. Fez trilhas para programas de TV como: Internet-se (Rede TV), Você Bonita (TV Gazeta), Mix Mulher (TV Gazeta), Os Impedidos (TV Gazeta), Estação Pet (TV Gazeta), CQC (TV Band) Vinheta Oficial TV Gazeta, entre outras. Também atuou em vários longas e curtas metragens, incluindo mixagem em 5.1 e serviços de pós-produção.