Tape hiss is the high frequency noise present on analogue magnetic tape recordings caused by the size of the magnetic particles used to make the tape. Effectively it is the noise floor of the recording medium. It can be reduced by the use of finer magnetic particles or by increasing the amount of tape used per second to record a signal. It can also be reduced by increasing the track width of the recording. A 3 dB reduction in hiss occurs for every doubling of the track width.
A number of noise reduction techniques can be used to reduce the impact of tape hiss, including Dolby NR and DBX, or, in case of video recording, frequency modulation of either the composite video signal, or the luma component.