that is often provided with the DAP on a CD-ROM included with the device, or downloaded from the manufacturer's website. Some devices simply appear as an additional disk drive on the host computer, to which music files are simply copied like any other type of file. Other devices, most notably the Apple iPod or Microsoft Zune, requires the use of special management software, such as iTunes or Zune Software, respectively. The music, or other content such as TV episodes or movies, is added to the software to create a "library". The library is then "synced" to the DAP via the software. The software typically provides options for managing situations when the library is too large to fit on the device being synced to. Such options include allowing manual syncing, in that the user can manually "drag-n-drop" the desired tracks to the device, or allow for the creation of playlists. In addition to the USB connection, some of the more advanced units are now starting to allow syncing through a wireless connection, such as via Wi-Fi or Bluetooth. Content can also be obtained and placed on some DAPs, such as the iPod Touch or Zune HD by allowing access to a "store" or "marketplace", most notably the iTunes Store or Zune Marketplace, from which content, such as music and video, and even games, can be purchased and downloaded directly to the device. Digital signal processing A growing number of portable media players are including audio processing chips that allow digital effects like 3D audio effects, dynamic range compression and equalisation of the frequency response. 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 compressors. Operation thresholds in adaptive audio compressors (in contrast to "ordinary" compressors) are regulated depending on ambient noise levels 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