Methods for identifying traces of compression in audio

Compression history of an audio may reveal very useful information when traces of tampering has to be investigated or quality of an audio has to be evaluated. Motivated by this, we introduce two methods that can discriminate between single and double compressed audio and can identify compression codec and bit rate of an audio. The first method utilizes audio quality measures to realize this and operates on decoded audio. The second method, alternatively, works on coded audio, effectively the audio bit stream, and characterizes randomness and chaotic properties of the bit stream to achieve these tasks. Unlike the existing work in the literature, which are proposed mainly for MP3 encoded audio, both methods can be applied to all encoding formats. Extensive tests have been performed to test the performance of both methods under various settings. Results show that both methods can be very reliably used to obtain information on compression history of an audio.