Telegraphing music

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I hope you'll indulge me on this series as I want to take it in smaller, slower bites one day at a time. I do get mail from time to time from those that want longer more detailed posts and are antsy to not be required to wait each day for more info and to those I apologize. My feeling on this particular subject is there's a lot to learn and understand for many and it's easier to grasp large complex issues in smaller more "edible" bites. It's also easier for me to write them and give you content with substance. Yesterday we covered a very basic view of digital audio vs. analog audio. Although there are numerous means of capturing, recording and playing back music other than analog, we're going to be focusing on just two: Pulse Code Modulation (PCM) and Pulse Density Modulation (PDM or DSD or SACD). Each of the two schemes we're focused on use identical "bits" to work their magic. The bits are what you're familiar with, 1's and 0's or, more descriptively, on and off states. These states are represented by simple square waves and, if you'll remember back to our last series on power, a square wave is nothing more than a quick transition from 0 volts to + volts and then back again. The easiest way to make a square wave is to use a battery and two wires. Connect the - wire of the battery to a DAC's ground and take the + wire and connect it to the DAC's digital input. To make a square wave, simply touch the + wire to the battery's + terminal and then remove it. Each time you touch it and remove it, the DAC see's what is known as a transition from 0 (no volts) to 1 (+ volts) and then back to 0. Do this multiple times in a row and you have a binary (meaning two states) "digital" data stream. If you do this in a particular order of 1's and 0's you create a type of code and if a device is used to create this code it is known as an "encoder". To unravel this code you need a "decoder" which can understand this code and give you a predetermined output based on this code. An ADC (Analog to Digital Converter) is a modern day analog to digital encoder and a DAC (Digital to Analog Converter) is a modern day digital to analog decoder that understands your "code" and puts everything back in original form. But there are far more basic digital encoders and decoders we may be familiar with: namely people. Perhaps the best known of these human powered digital encoder/decoder schemes we would all be familiar with was invented by a fellow named Samuel Morse and later became known as Morse Code. The device he used was called the telegraph. In 1836 Morse and a few other inventors were determined to send messages long distances with wires. Without getting too in depth on the history, Morse created a code of 1's and 0's that enabled an operator to convert language and numbers into a binary code and transmit that code over wires and be received many miles away and then reconverted back to its original form. As a point of interest, Morse couldn't use on and off for his binary signal because the off state wouldn't be recognized. Instead of on and off, Morse code used long and short - but the idea is exactly the same. The beauty of this code scheme is that the quality of the conversion process, from language to binary and back again, could be all over the map and still work. That meant poor translators as well as expert translators could use the code to send intact precise messages down a wire and, eventually, through the air and the results would always be repeatable and identical. Understanding how the telegraph is the same as digital music is important because the concept we're going to understand is embodied in this scheme of encoding and decoding one form of data to another.
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Paul McGowan

Founder & CEO

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