| Due to the physical properties of electronic components, DC offset will occur to some extent in all audio recordings. DC offset is the effect of direct current on an audio recording, and causes the audio signal to no longer oscillate around the absolute zero quantization level. The mean amplitude of a recording is calculated to determine the global amount of DC offset. Measuring the offset, its change over time, and its standard deviation can be used during forensic examination to aid in determining the authenticity of a recording as well as for exclusionary purposes when multiple recorders could possibly be the source of a recording. The scope of this thesis is to measure the DC offset that occurs in recordings made by Apple mobile devices running on iOS, to quantify the uniqueness of this offset within this family of devices as well as against previously tested audio recording devices, and to see if different hardware and apps affect the offset. To accurately determine this, multiple apps were tested in conjunction with the built-in microphone, the Apple EarPods that come with the iPhone 5, and the Apple Earphones that come with previous iPhone models. Furthermore, all recordings were made in laboratory conditions with a minimum amount of outside noise, only the app making the current recording was open, Auto-Brightness was switched off, and all outside connectivity (wireless, Bluetooth, 3G, 4G, LTE) was turned off. |
