Editing Portable media player (section)

===Natural mode===
Natural mode is characterised by subjective effect of balance of different frequency sounds, regardless of level of distortion, appearing in the reproduction device. It is also regardless of personal user's ability to perceive specific sound frequencies (excluding obvious hearing loss). The natural effect is obtained due to special sound processing algorithm (i.e. "formula of subjective equalisation of frequency-response function"). Its principle is to assess [[frequency response function]] (FRF) of mediaplayer or any other sound reproduction device, in accordance with audibility threshold in silence (subjective for each person),<ref>{{cite web|url=http://www.aist.go.jp/aist_e/latest_research/2003/20031114/20031114.html|title=Full Revision of International Standards for Equal-Loudness Level Contours (ISO 226)|work=aist.go.jp|url-status=dead|archive-url=https://web.archive.org/web/20060115001541/http://www.aist.go.jp/aist_e/latest_research/2003/20031114/20031114.html|archive-date=15 January 2006|df=dmy-all}}</ref> and to apply gain modifying factor. The factor is determined with the help of integrated function to test audibility threshold: the program generates tone signals (with divergent oscillations – from minimum volume 30–45&nbsp;Hz to maximum volume appr. 16&nbsp;kHz),<ref>{{cite web|url=http://newt.phys.unsw.edu.au/jw/hearing.html|title=Free hearing test on line: Equal loudness contours and audiometry|work=unsw.edu.au}}</ref> and user assess their subjective audibility. The principle is similar to [[Audiometry#Types|in situ audiometry]], used in medicine to prescribe a hearing aid. However, the results of test may be used to a limited extent as far as FRF of sound devices depends on reproduction volume. It means correction coefficient should be determined several times – for various signal strengths, which is not a particular problem from a practical standpoint.