4gb data storage will give approximately 1000+ hours digital recording or  Approximately 1000 MP3-encoded files can be stored in 4 GB of memory on an digital voice recorder, memory card, or computer disk.

Many digital voice recorders and "MP3" players can also store music that's been saved in Microsoft's own compression format, called WMA. WMA files take about half the space of MP3 files, so a digital voice recorder that can handle them can store about 1000 WMA-formatted songs within 4 GB of space.