WOK has released Loudness Dynamic EQ, a free for download VST plugin for Windows.
This VST plugins simulates the loudness button from the old Hi-Fi amps, which alters the frequency response curve to correspond roughly with the equal loudness characteristic of the ear at lower volumes.
The level of high and low frequencies is increased at low listening levels, to compensate for the fact that as the volume of audio decreases, the ears lower sensitivity to extreme high and low frequencies may cause these signals to fall below threshold. As a result audio material may seem to become ‘thin’ sounding at low volumes, losing bass and treble, the ‘Loudness compensation’ button (often just labelled ‘Loudness’ or ‘Loud’) is intended to rectify this situation.
Loudness Dynamic EQ plugin is available for free as a 32bit VST plugin for Windows.
UPDATE: This plugin is no longer available! Check: Free VST Plugins