fig1 is a schematic diagram showing an example of an authorized playback environment asu , such as the inside of a passenger transport means , especially an aircraft , a train , etc . an entertainment system us is provided in this authorized playback environment asu . with the entertainment system us users , e . g . passengers of the means of passenger transport can be provided with data content di , especially audio data content and / or video data content , e . g . as an entertainment program . this data content di is for example audio and / or video data content such as films , music clips , series etc . which is made available for example to an operator of the means of passenger transport in a hospitality window — i . e . before it appears on the market , on dvd for example . output units ae 1 , ae 2 , . . . , aen are provided in the authorized playback environment asu for output , retrieval by a user and playback of the data content di . these output units ae 1 , ae 2 , . . . , aen are linked via a distribution device a to the entertainment system us , wherein the data content di is transported via this distribution device a from the entertainment system us to the output units ae 1 , ae 2 , . . . , aen . permanently installed screens can be provided for example in the authorized playback environment asu as output units ae 1 , ae 2 , . . . , aen , which are connected for example via cabling as the distribution device a to the entertainment system us . however it is also possible for the output units ae 1 , ae 2 , . . . , aen to be embodied as what are known as personal entertainment devices ( e . g . smart phone , tablet pc , etc . ), which are made available to users or for mobile terminals belonging to the users , such as smart phones , tablet pcs , laptops , etc . to be able to be used as output units ae 1 , ae 2 , . . . , aen for output and playback of the data content di . in this case a radio communication systems , such as wirelesslan , gsm , umts , gsm - on - board etc . can be used as the distribution device a for transmission of the data content di for example . if for example the entertainment system us is put into operation once the means of passenger transport with the authorized playback environment asu has been started , in a first method step 1 data content di is made available by the entertainment system us . this data content di can for example be retrieved and output via selection on the output units ae 1 , ae 2 , . . . , aen located in the authorized playback environment . in this case in a second method step 2 an interference signal sg is added to the data content di such that when the data content di is played back outside the authorized playback environment asu interference and / or a marked reduction in quality of the data content di is brought about . i . e . reproduction of the data content di in an unauthorized environment is permanently and clearly disrupted by the interference signal sg . the interference signal sg can in such cases be mixed into the data content di before the transport or transmission of the data content to the output units ae 1 , ae 2 , . . . , aen on the entertainment system us . as an alternative the interference signal sg can for example also be added to the data content during or before the data content di is played back on the entertainment system us . furthermore there is the option of only adding the interference signal sg to the data content di in the output units ae 1 , ae 2 , . . . , aen . the interference signal sg , which is added for example in the second method step 2 before the transmission of the data content di , is ideally mixed into an audio component of the data content di . in such cases noise can be used as an interference signal sg for example . this noise sg is not perceived ( subjectively ) in the authorized playback environment asu as a result of existing background noises ( e . g . aircraft noises , etc .) or a level of sound . in a quiet environment such as a home cinema for example , permanent interference is generated during the reproduction of the data content di by the noise sg . the data content di or the audio component of the data content di is “ cloaked ” by the noise sg as interference signal sg , which is why this can also be referred to as passive audio noise cloaking . as an alternative the noise signal sg used or the passive audio noise cloaking can be combined with active noise reduction technologies . in this case , for interference signals sg in the authorized playback environment asu existing or known background and / or interference noises are taken into account . this means that a combination of a noise and a phase - shifted interference noise of the authorized playback environment asu is used as the interference signal sg ( i . e . a phase shifted real noise through which a phase cancellation with the existing interference noises is brought about ). the effect of such a combination is that on the one hand an improvement in the playback quality of the data content di , especially of the audio component , is achieved in the authorized playback environment asu . on the other hand in a non - authorized playback environment the result is a significant worsening of the playback quality of the data content di , which means that the copy and / or further copies of the data content di are of no interest . active noise reduction technologies currently enable especially low - frequency background or interference noises to be successfully reduced for example since with high - frequency sound waves a distance between a sound source and the inner ear of the user is too large to effect an exact phase cancellation of the two phase - shifted noises . in addition with short waves a distance between a microphone and the sound source or the headphones must also be relatively short . since however for example in means of passenger transport such as aircraft , low - frequency interference noises — for example in a frequency range of approximately 50 to 600 hz — arise , the combination of interference signal sg or noise sg with an active noise or interference noise reduction technology can be used to improve the playback quality of the data content di e . g . in an aircraft as well as for a further protection of the data content di ( e . g . from unauthorized copying , filming , etc .). this combination can also be referred to as active audio noise cloaking . after an addition of an interference signal sg in the second method step 2 , the data content is then forwarded in a third method step 3 by the distribution device a to the output units ae 1 , ae 2 , . . . , aen . in a fourth method step 4 the data content di can then be output and played back on the output units ae 1 , ae 2 , . . . , aen . a mixing or addition of an interference signal sg into the data content di , especially to the audio component or to an audio track of the data content di , is therefore above all also relevant because , according to the motion picture association of america approximately 90 % of unauthorized copying of data content di , especially of video data content , by filming the data content , is undertaken by means of cameras , camcorders , copying software etc . it is precisely during transmission and playback of the data content di however on so - called personal entertainment devices or mobile terminals of a user that the illustrated method can very simply and quickly and also at no great expense , combine an additional interference signal sg ( e . g . conversation noises , background noise etc .) with existing data content di , so that an unauthorized copy exhibits greatly reduced quality and disruptions . this copy is thus worthless and of no interest . thus with the illustrated method , an additional protection — as well as conventional protection mechanisms — can be achieved for data content di , especially on playback in means of passenger transport such as aircraft for example . especially in the variant of what is known as active audio noise cloak or audio noise cloaking ( equals a combination of noise and a phase - shifted interference noise of the authorized playback environment asu into an interference signal sg ) on the one hand an improvement of the playback quality in an authorized playback environment asu ( e . g . aircraft , etc .) can be achieved while on the other hand , in other playback environments , which for example access an illegally created copy , etc . a significant deterioration of the playback quality occurs . while specific embodiments have been described in detail , those with ordinary skill in the art will appreciate that various modifications and alternative to those details could be developed in light of the overall teachings of the disclosure . for example , elements described in association with different embodiments may be combined . accordingly , the particular arrangements disclosed are meant to be illustrative only and should not be construed as limiting the scope of the claims or disclosure , which are to be given the full breadth of the appended claims , and any and all equivalents thereof . it should be noted that the term “ comprising ” does not exclude other elements or steps and the use of articles “ a ” or “ an ” does not exclude a plurality .