Bit errors are falsifications of a binary signal element during transmission, processing or storage. The probability of this corruption can depend on the original signal state, i.e. it can be different for the corruption from "0" to "1" than for the corruption from "1" to "0".
Causes for bit errors are e.g. disturbances of the transmitted signal, noise, crosstalk or a too high path attenuation. The effects of these causes depend, among other things, on the code used, whereby with some codes one code error can cause several bit errors.
During data transmission, a bit error disturbs a character. In order to be able to detect these disturbances, blocks of a certain length are generally transmitted. With the help of a checksum transmitted along with the data, the receiver checks the correctness of the transmitted data and can request the retransmission of the block in case of errors. In classic analog telephony, bit errors have the effect of clicks and pops. A bit error rate of `10^-2` is noticeable as strongly disturbing pattering, at `10^-3` the pattering dissolves into a dense sequence of pops, which changes into single pops at a bit error rate of `10^-4`. At `10^-5` only single pops are audible and bit error rates of `10^-6` do not affect speech transmission at all.