# Data Recording: Modulo Counting - Part 18

The mathematics of finite fields and sequences seems to be a long way from everyday life, but it happens in the background every time we use a computer and without it, an explanation of modern error correction cannot be given.

Fig.1 - In two's complement, the circular number field is redefined to begin half a turn away from zero, so zero is in the middle of the scale and positive or negative values can be encoded.

Fig.2 - A three bit twisted ring counter and the sequence it goes through. Mathematically it is raising the starting value a to higher and higher powers.

Fig.3 - The addition, modulo-2, of a pseudo-random sequence to serial data breaks up long run-lengths and reduces any DC component.

Fig.4 - The randomizer used in DVB.

Fig.5 - Here a twisted ring counter is used to calculate redundancy on four data bits A -D to make a 7,4 code. The three redundant bits are left in the register after the data are clocked in.

# Audio Levels - Part 4

There are two basic reasons to know the level of an audio signal. One of these is more technical and one of them is more subjective.

# Data Recording: Cyclic Redundancy Checks - Part 19

The CRC (cyclic redundancy check) was primarily an error detector, but it did allow some early error correction systems to be implemented. There are many different CRCs but they all work in much the same way, which is that the…

# Audio Levels - Part 3

The traditional level standards were based on electrical signals of specified power. When these signals are recorded on media, or transmitted in other ways, these definitions no longer apply.

# Advances In 12G-SDI:  Part 2 - 12G-SDI Technology

In the last article in this series we looked at how SDI has developed over the years to reach an incredible 47.52Gbits/sec for quad-link 12G. In this article, we dig deeper and uncover the technology enabling SDI and its…

# Audio Levels - Part 2

The deciBel is a logarithmic ratio that happens to express quite well both the signal loss in transmission lines and the subjective sense of loudness in human hearing.