Editing Portable media player (section)

==Digital signal processing==
A growing number of portable media players are including audio processing chips that allow digital effects like [[3D audio effect]]s, [[dynamic range compression]] and [[Equalization (audio)|equalisation]] of the [[frequency response]].<ref>{{cite web|url=http://www.cirrus.com/en/products/software/consumer.html|publisher=[[Cirrus Logic]]|title=Consumer Audio Software|quote=Virtual Stereo Surround – Multiband Compressor – Tone Control – Bass Manager – Bass Enhancer – Dynamic Volume Leveler – Multichannel Surround – Crossbar Mixer – Speaker Protection – Dolby Digital Post-processing Support|url-status=live|archive-url=https://web.archive.org/web/20150429113945/http://www.cirrus.com/en/products/software/consumer.html|archive-date=29 April 2015|df=dmy-all}}</ref><ref>{{cite web|quote=bass management, 3D virtual surround, Lucasfilm THX5.1, soundfield processing, and advanced equalization|url=http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=DSP56362&fsrch=1&sr=4&pageNum=1|title=Freescale 24-bit Symphony DSP|publisher=Freescale semiconductor|url-status=live|archive-url=https://web.archive.org/web/20150710080830/http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=DSP56362&fsrch=1&sr=4&pageNum=1|archive-date=10 July 2015|df=dmy-all}}</ref><ref>{{cite web|url=http://www.am3d.com/home-english/android/android-solution.aspx|title=Android solution|publisher=am3d.com|url-status=dead|archive-url=https://web.archive.org/web/20150530210929/http://www.am3d.com/home-english/android/android-solution.aspx|archive-date=30 May 2015|df=dmy-all}}</ref><ref>{{cite web |url=http://www.cirrus.com/en/pubs/whitePaper/smartphones_wp.pdf |title=Archived copy |access-date=2015-04-25 |url-status=live |archive-url=https://web.archive.org/web/20150923203714/http://www.cirrus.com/en/pubs/whitePaper/smartphones_wp.pdf |archive-date=23 September 2015 |df=dmy-all }}</ref> Some devices adjust loudness based on [[Fletcher–Munson curves]]. Some media players are used with [[Noise-cancelling headphones]] that use [[Active noise reduction]] to remove background noise.

===De-noise mode===
De-noise mode is an alternative to [[Active noise reduction]]. It provides for relatively noise-free listening to audio in a noisy environment. In this mode, audio intelligibility is improved due to selective gain reduction of the ambient noise. This method splits external signals into frequency components by "filterbank" (according to the peculiarities of human perception of specific frequencies) and processing them using adaptive [[audio compressor]]s. Operation thresholds in adaptive audio compressors (in contrast to "ordinary" compressors) are regulated depending on [[ambient noise level]]s for each specific bandwidth. Reshaping of the processed signal from adaptive compressor outputs is realised in a synthesis filterbank. This method improves the intelligibility of speech signals and music. The best effect is obtained while listening to audio in the environment with constant noise (in trains, automobiles, planes), or in environments with fluctuating noise level (e.g. in a metro). Improvement of signal intelligibility in condition of ambient noise allows users to hear audio well and preserve hearing ability, in contrast to regular volume amplification.

===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.

===Sound around mode===
Sound around mode allows for real time overlapping of music and the sounds surrounding the listener in their environment, which are captured by a microphone and mixed into the audio signal. As a result, the user may hear playing music and external sounds of the environment at the same time. This can increase user safety (especially in big cities and busy streets), as a user can hear a [[Footpad|mugger]] following them or hear an oncoming car.