Pre-processing individual audio items in a media project in order to improve real-time processing of the media project

Some embodiments of the invention provide a method of processing audio data while creating a media presentation. The media presentation includes several audio streams. The method processes a section of a first audio stream and stores the processed section of the first audio stream. The method also processes a section of a second audio stream that overlaps with the processed section of the first audio stream. The method then processes the section of the second audio stream independently of the first audio stream. In some embodiments, the method processes the first audio stream section by applying an effect to the first audio stream section. Also, in some embodiments, the processing of the first audio stream section also entails performing a sample rate conversion on the first audio stream section.