Longitudinal wave and seismic P-waves (created by earthquakes and explosions). In longitudinal waves, the displacement of the medium is parallel to the propagation of the wave, and waves can be either straight or round. A wave along the length of a stretched Slinky toy, where the distance between coils increases and decreases, is a good visualization. In the case of longitudinal harmonic sound waves, the frequency and wavelength can be described by the formula where: The quantity "x"/"c" is the time that the wave takes to travel the distance "x". The ordinary frequency ("f") of the wave is given by The wavelength
Constant-weight code threshold. Most line codes use either a constant-weight code, or a nearly-constant-weight paired disparity code. In addition to use as error correction codes, the large space between code words can also be used in the design of asynchronous circuits such as delay insensitive circuits. Constant-weight codes, like Berger codes, can detect all unidirectional errors. The central problem regarding constant-weight codes is the following: what is the maximum number of codewords in a binary constant-weight code with length formula_1, Hamming distance formula_2, and weight formula_3? This number is called formula_4. Apart from some trivial observations, it is generally impossible to compute