The storage of an analogue signal on tape works well, but is not perfect. In particular, the granular nature of the magnetic material adds noise to the signal, which is usually heard as tape hiss. Also, the magnetic characteristics of tape are not linear, they exhibit a characteristic hysteresis curve. The curvature causes unwanted distortion of the signal. Some of this distortion is overcome by using an inaudible high-frequency AC bias signal when recording, though the amount of bias needs careful adjustment for best results. Different tape material requires differing amounts of bias, whics is why most recorders have a switch to select this (or switch automatically). Additionally, systems such as Dolby B and Dolby HX-Pro have been devised to ameliorate some of the noise and distortion problems.
There are a wide variety of tape recorders in existence, from small hand held devices to large multitrack machines which are roughly equivalent in size to a large, highbacked armchair.
While they are primarily used for sound recording, tape machines were also important for data storage before the advent of floppy disks and CDs, and are still used today, although primarily to provide a nonvolatile backup to hard disk drives.