Tech Tip:Digital Audio Basics, Part 1
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Part 1: The Nature of Sound / A/D Converters
If you have done any reading about modern recording equipment and techniques, no doubt you've come across the phrase "digital audio" a number of times. At this point, you may still be a bit unclear about what exactly digital audio is and how it's created. You may think of digital audio as the sound that comes out of your computer soundcard or those waveforms that show up in your digital audio sequencer, but there's a lot more to understand about how the audio gets into your computer or digital audio recorder in the first place.
The Nature of Sound
The waveform you see when you record digital audio on your computer represents the relation between these two characteristics, with amplitude on the vertical axis (up and down) and frequency on the horizontal or time axis (left to right).
The Analog-to-Digital Converter
Before even hitting the A/D converter, every cycle of a soundwave is turned into an electronic signal by the microphone or instrument pick-up. This signal fluctuates between a positive and a negative voltage to represent the upper and lower amplitudes of the soundwave cycle. The converter, found just after the analog input in all digital recorders, digital mixers and soundcards, takes a series of "snapshots" or samples of this incoming electronic signal and converts it into a series of binary numbers made up of ones and zeroes. This numerical list of information is then stored on whichever medium the recorder uses, such as a hard drive or a tape, or then passed digitally to the next phase of the signal chain.
The A/D conversion is a crucial aspect of the digital recording process because it determines the ultimate quality of the digital representation of the sound. With more snapshots, there is more digital information and therefore a more accurate representation of the original, analog sound. Imagine trying to describe the most beautiful sunset you've ever seen to a friend: The more words you use to describe it, the more evocative a description you can give, creating a clearer picture in the mind of your friend. The same is true of conveying an audio signal (the sunset) to a computer (the friend). The more numbers you use to convey the details, the better job the computer program can do in recreating the original audio.
Essentially, that's what happens every time you record a signal into a digital audio recorder. The A/D converter takes as many snapshots of the sound as possible and converts them into a string of binary numbers. Turning audio into ones and zeroes requires the computer to do a lot of number-crunching, so it's understandable that digital audio is taxing on a computer's hardware and processor. With that in mind, let's take a look at the two primary characteristics of a digital converter that determine the quality of the digital recording: sample rate and bit depth.
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