I have created a DocumentGalleryModel to read the audio files from the mobile and sort according to file name

rootType: DocumentGallery.Audio
properties: ["url","fileName","path"]
sortProperties: [ "fileName" ]

What I want is that all files of the device be sorted according to file name. But when I read the result from the view, the files within a folder/album are sorted and appended to the list. The sorting did not happen for the entire list of files in the device. How can I use the sortProperties to sort all files in the device. Thanks in advance