When looking for audio to include in a multimedia project, it is important to be aware of how format and sample rate can impact the quality of your audio. Mp3 files compress sound files while .wav files are uncompressed and can store higher quality audio.
The standard sample for a project that combines video, image and audio elements is 48kHz. It is important that you make sure all of the files you download and record are the sample sample rate. You can check your files resolution by opening in a media player or video application and checking the properties of the audio file.
Audio libraries listed here contain sounds, music, and other audio. Some are out of copyright or openly-licensed, and some are under copyright and would require a fair use assessment before use. Be sure to double-check the terms of the license for anything you want to use to see what you can do with it and how to credit the creator
Starting points - large audio libraries:
Naxos is the world's current leading producer of classical music. The collection offers the complete Naxos, Marco Polo, and Da Capo catalogues, as well as selected works in Jazz, Folk, and World music.
Naxos Music Library -- Jazz
Based on the Naxos Jazz label, this collection offers contemporary jazz from around the world, featuring artists and ensembles from the US, Scandinavia, Germany, Australia and New Zealand. This database includes selected performances from additional labels, such as Chesky, innova, Intuition, Jazzwerkstatt (based in Berlin), Yellowbird, and especially Fantasy® (which includes the Debut and Galaxy labels).
Database of Recorded American Music
Collection of sound recordings documenting American music largely ignored by the commercial recording companies.
Music Online -- Alexander Street Press
One interface to search the Alexander Street Press music databases described below.