ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
https://netflixtechblog.com/optimizing-the-aural-experience-on-android-devices-with-xhe-aac-c27714292a33
Yes, it's an advertisement for Netflix, but it's a good tutorial on the problem associated with audio levels and dynamic range across different formats.
cheers- geoff
Thank you Geoff for the interesting article.
I have always assumed that the loudness function was designed for compensating the human hearing at lower levels. The human ear would be less sensitive for lower and higher frequencies at low level. Therefore a well designed loudness circuit (as was with B&O's version) gained only the bass and treble section at lower volumes and the gaining decreased when the volume was turned up.
You could check that when you pushed the loudness button on and off when your volume was more turned up. At about 3/4 off the maximum volume you shouldn't hear any difference, as if I remember that some (japanese)brands would still gain these bands rather noticable.
This doesn't match what I read in the article, where gaining is done over the complete frequency range at lower levels. Or did I miss something?
The problem is that there are two definitions of "loudness".
One is the one you're talking about - a bass (and possibly treble) boost to compensate for the equal loudness contours (a.k.a. Fletcher Munson curves).
The other is the definition that psychoacoustics people use - which is a perceptual measure of how loud things sound. Measuring sound pressure level (SPL) does not always correlate with how loud things sound to us for a lot of different reasons. One of them is the equal loudness contours (a 3 kHz sine wave at 100 dB SPL is painful whereas a 20 Hz sine wave at 100 dB SPL is starting to have some nice bass), another is temporal ( (a 3 kHz sine wave at 100 dB SPL is painful whereas a 1 ms click at 100 dB SPL is noticeable, but not worrisome). So, the "how loud things sound" definition of loudness results in measurements like "sones" which are related to dB SPL, but weighted with frequency - for example.
The "loudness" they're talking about in this article is the second definition - which should help to make things make more sense.
Cheers-geoff
Thank you Geoff for taking time to help solving my confusion.
Btw. My compliments for the entertaining informative films you've made so far on Youtube. I regularly suggest these films to people who want to know a bit more about what happens inside their rooms with the acoustics.
Are there any new episodes to be expected?