A dropout is a small loss of data in an audio or video file on tape or disk. A dropout can sometimes go unnoticed by the user if the size of the dropout is small. Error correction schemes can compensate for the dropout by filling in data where a dropout is detected. With a larger section of missing data, the user will see or hear the error.
The reason for a dropout can be bad tape stock, a bad block on a hard disk, dirt, the age of the tape or disk, or something else. Older tapes, especially those dating to the analog era, are more susceptible to dropouts as they age. The magnetic particles on the tape become detached from the backing material, resulting in what is commonly known as shedding. Larger dropouts can be quite serious. On the master tape of a vintage recording, a dropout could be large enough to render a selection unusable. In a video studio, a dropout on the SMPTE Time Code track could cause the machines slaving to the Time Code track to stop momentarily.