IntroductionLoudness provides a more natural sounding volume control based on the frequency response characteristics of human hearing.
Human hearing does not have a flat frequency response as volume changes. You can read more about this phenomenon here:
http://en.wikipedia.org/wiki/Fletcher%E2%80%93Munson_curvesWhen the Loudness feature is enabled in Media Center, it uses (roughly) the ISO 226:2003 curves as the volume is decreased to provide a more linear sounding volume.
This feature was added to Media Center 18.0.91.
InstructionsTo use Loudness, you must also use Internal Volume. This is because the Internal Volume provides the internal headroom necessary to do frequency corrections without clipping. Also, Loudness requires knowing the volume level in decibels, which is only possible with Internal Volume (System Volume reports in percent, and there's no standard conversion to decibels that works with all hardware). More on volume here:
http://wiki.jriver.com/index.php/VolumeTo enable loudness, click the little speaker to the left of the volume slider and check 'Loudness'. The setting is also available from the main menu (under Player > Volume) and also in Options > Audio.
If you set the 'Reference level' for Internal Volume in Options > Audio, this will also define the zero point for Loudness. Loudness correction makes no changes at or above the reference level (defaults to 100%). It only engages as the volume goes below the reference level.
TechnicalsAt the reference level (100% by default), no correction is applied. As the volume is lowered, frequency correction is applied. Roughly speaking, the bass is turned down about half as much as the rest of the audio when the volume goes down. The same is done, but to a lesser extent, at high frequencies. This 'U-shaped' volume is roughly the inverse of the differences between ISO 226:2003 curves as the volume is reduced.
If you're curious, you can play pink noise (Tools > Advanced Tools > Create Test Clips...) and watch DSP Studio > Analyzer as you change the volume. You'll be able to see the frequency correction taking place.
Doing a
perfect job of loudness correction would be extremely complex. It would likely need a real-time microphone at the listening position. So it's important to remember this solution is an approximation. It's a hopefully good approximation, but it's not aiming to account for all the complexities of the loudness issue.
MoreThe discussion that led to the addition of Loudness can be found here:
http://yabb.jriver.com/interact/index.php?topic=76060.0