Pseudo Random Bit Sequence is used to scramble data in a communication system for security reasons. Some of the applications are in Cryptography, computer data security and integrity, prevent unauthorized usage of cable TV line by scrambling data, generating elaborate tonal structures unlike any known instrument, instrument voicing etc. These sequencers have several nice features. First they can be of maximal length, that is they can be as long as a register sequence can possibly be. This turns out to be one less than 2n, so that the circuit is essentially as efficient as a binary counter. Second, the number appears in an apparently random order, although, of course they repeat every time the sequence is clocked completely through 2n-1 counts. The same noise pattern repeats every n-1 clock cycles. This is used for testing audio systems. In fact pseudo noise turnout to be better than real noise. The randomness is complete over one total cycle, where real noise requires a very long (ideally infinite) time average to get true randomness. This PRBS generator makes use of 63-state count using 6 registers. The binary outputs of this sequencer are processed to obtain random analog levels. As a result of this a series of uniformly timed steps of random analog values can be generated. This can be used to test a musical system. It is possible to change the bit sequence by changing the count sequence using patch chords. |
