Music Collection of the National and University Library in Zagreb comprises part of Croatian musical heritage, including music prints, music manuscripts and a collection of sound recordings. The text gives an overview of the activities connected to the Music Collection digitization, with an emphasis on the digitization of historical sound recordings on 78 rpm gramophone records, which constitute the oldest and important part of Croatia's musical sound heritage. Due to its historical and cultural significance some of the material held by the Music Collection, represents a priority when it comes to the protection, preservation and accessibility. With the goal of preserving and making available part of Croatian sound history, the Library launched a project for digitizing historic sound recordings. The project asserted itself as a good solution for preserving and making a valuable part of Croatian sound heritage accessible online. The project's results are presented in the virtual collection Sounds of the past which contains high-quality metadata as well as bio-bibliographic and contextual data. As inseparable parts of the old gramophone record, original record labels can be seen there, as well as what record covers and publisher's catalogues looked like. Its additional value lies in the accompanying materials, which include texts and clippings from the leading newspapers of that time. The major part of the collection of sound recording's collection comprises items released by the Edison Bell Penkala company, an important platform for producing and publishing of gramophone records situated in Zagreb during the 1920s.