SAN FRANCISCO  Some of the largest book publishers in the world are stripping away the anticopying software on digital downloads of audio books.

The trend will allow consumers who download audio books to freely transfer these digital files between devices like their computers, iPods and cellphones  and conceivably share them with others. Dropping copying restrictions could also allow a variety of online retailers to start to sell audio book downloads.

The publishers hope this openness could spark renewed growth in the audio book business, which generated $923 million in sales last year, according to the Audio Publishers Association.

Random House was the first to announce it was backing away from D.R.M., or digital rights management software, the protective wrapping placed around digital files to make them difficult to copy. In a letter sent to its industry partners last month, Random House, the world’s largest publisher, announced it would offer all of its audio books as unprotected MP3 files beginning this month, unless retail partners or authors specified otherwise.