Signal Converters (ADC & DAC)

1903 - 2000
Signal converters have been around in analog form at least since the invention of the telegraph, and possibly as far back as the ottoman empire. However in their most familiar iterations, as digital converters, they have been around for roughly 70 years, since Wilkinson, and others utilized the semi-conductive properties of various metalloids to create circuits that processed analog signals (Walt, 2009).
There are two general types of converters, Analog to Digital (ADC) and Digital to Analog (DAC). The way they work is by converting a sound into an electric current, and then further converting this into binary code, and then back into an electrical current. There are several ways to set up an ADC and a DAC, but they all involve capacitors and comparators which are ways of holding charges, and ways of comparing them (Bucknell: Electrical Engineering A/D Converters).
When an analog signal is run through an ADC, it has a certain voltage, which changes as the signal fluctuates. This change in voltage is compared by the comparators, which are themselves set to register a range of voltages corresponding to a range of code which is then processed as a series of discrete ‘bytes’. These bytes can then be stored or played back using a DAC. One of the most important aspects of this kind of design is the clock rate, which is the baseline rate at which the sample is taken. Without a constant rate, typically measured as the rate of decay, it would be impossible to accurately sample the continuous analog signal. This overall sampling process is called Pulse Code Modulation (Walt, 2009).
The invention and application of signal converters remains crucial to all forms of recording, particularly today, where nearly everything is stored digitally. For example, while CD’s have pits and lans, these are not the same as grooves in a vinyl record, because the pits and lans in a CD correspond to the on and off in a circuit i.e. the 1’s and 0’s of binary. Likewise, in magnetic recording, both disc and flash, the polarization of the magnetic particles correspond to the 1’s and 0’s of binary.
Kester, Walt. "Analog to Digital Conversion." Mixed-signal and Digital Signal Processing ICs | Analog Devices. Accessed December 3, 2015.

"Analog To Digital (A/D) Converters." Electrical Engineering. Accessed December 3, 2015.