I need to apply the reverb filter to my sound file in my ipad app. I just found a keyword AVMetadataID3MetadataKeyReverb in the apple documentation, but not able to get how to use it. This has been added from iOS 4.0.
The AVMetadataID3MetadataKeyReverb constant represents the RVRB field of and ID3(V2) tag - which is simply a piece of metadata that's part of an audio container file (like MP3). The constant isn't related to applying an actual reverb effect to a piece of audio data, but to identifying different parts of ID3 tags when using the AV Foundation to retreive them from an audio file... Later when a supporting audio player plays those files it reads the tags and applies different filters (like the Reverb one) in real time while playing the file.
If you want to modify this value, you'll have to use some external library as Audio Toolbox only knows how to read ID3 tags not writing them. Check out TagLib
If you want to apply effects to some audio data check out BASS, they have an iPhone library, and many effects including reverb. There might be alternatives though.
来源：https://stackoverflow.com/questions/4813746/how-to-apply-reverb-filter-or-any-other-sound-effect-to-a-wav-sound-file