Sony MZ-NH1 - Manual (Page 119)

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On copyright protection
The OpenMG technology allows you to enjoy digital music, while maintaining the
copyrights of its holders. SonicStage encrypts audio files in OpenMG format and stores
them on the hard disk of your computer to prevent unauthorized distribution.
Restrictions on audio content
High-quality digital audio content is widely available through music distribution services
on the Internet. To protect the copyrights of its holders from unauthorized distribution,
some audio content is distributed with certain restrictions on recording and playback. For
example, the playback period or playback count for the data may be limited.