I have blogged about loudness for the web and mobile devices before (Mixing Levels for Mobile Devices and Online Music Loudness), and things are slowly starting to become a bit more standardised. The AES Technical Council released a recommendation paper late last year which is fairly in line with stuff I have previously included in my blog, but with some more details. The key recommendations from the paper are:
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It is recommended that the Target Loudness of the stream not exceed -16 LUFS: to avoid excessive peak limiting, and allow a higher dynamic range in a program stream.
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It is recommended that the Target Loudness of a stream not be lower than -20 LUFS: to improve the audibility of streams on mobile devices.
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It is recommended that short-form programming (60 seconds or less) be adjusted by constraining the Maximum Short-term Loudness to be no more than 5 LU higher than the Target Loudness: This ensures that commercials and similar short-form content are consistent with the stream loudness.
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It is recommended that the maximum peak level not exceed ?1.0 dB TP: to prevent clipping when using lossy encoders.
The full paper is available at:
http://www.aes.org/technical/documents/AESTD1004_1_15_10.pdf
For a neat, less technical explanation of this issue, here is a neat little video produced by MeterPlugs:
Their current recommendations are:
• iTunes: PLR 15
• YouTube: PLR 12
• Spotify: PLR 10