This clock acts kind of like a police officer in the middle of an intersection directing the traffic of bits based on time in your computer. So who is telling these audio devices when to start taking samples and at what rates to do so? Here is where the device’s internal clock comes in.Įvery computer device from your laptop to your USB audio interface has some sort of clock in it whether it’s in the processor’s logic board or in a separate chip. The word length or bit depth describes in computer language to the device how discrete and fine to make the dots in the painting. Each chop is described by a “word” in the digital realm that translates to a computer value by the device doing the sampling. When you have higher bit depths, the waveform is “chopped” into smaller pieces creating increased articulation of the signal. Landscape portrayed with dots of larger sample size As a result, the level of articulation within the drawing significantly increases. As you paint with smaller and smaller dots closer together, the dots start approaching the characteristics of lines the smaller and closer together they get. Imagine you are painting a landscape with dots of paint: if you used large dots to draw this landscape, the image would be chunkier and perhaps it would be harder to interpret the image being conveyed. Think of bit depth as the “size” of the “chops” of our waveform where the higher the bit depth, the greater discretization of our samples. Not only is the integrity of our digital waveform affected by the minimum number of samples per second, but bit depth affects it as well. Another important term for us to discuss here is bit depth and word length when talking about digital audio. This means that those frequencies sampled above the range of human hearing can affect the frequency response of our audible bandwidth given high enough amplitude! So without going down the rabbit hole of recording music history, CDs, and DVDs, you can see part of the reasoning behind these higher sample rates is to provide better spectral bandwidth for what us humans can perceive. According to “Introduction to Computer Music: Volume One”, by Professor Jeffrey Hass of Indiana University, these partials or overtones above the sample frequency range are “mirrored the same distance below the Nyquist frequency as the originals were above it, at the original amplitudes” (2017-2018). The long answer is that it doesn’t sound good because the frequency response of the sampled waveform is affected by frequencies above the Nyquist frequency due to aliasing. Soooo why don’t we have sample rates of 40 KHz? Well, the short answer is that it doesn’t sound very good. So if the human ear can hear 20Hz-20kHz, then in theory in order to reproduce the frequency spectrum of the human ear, the minimum sample rate must be 40,000 samples per second. *Sampling theory is not just for audio, it applies to imaging too! See references “The Nyquist Theorem states that in order to adequately reproduce a signal it should be periodically sampled at a rate that is 2X the highest frequency you wish to record.” Why do these specific numbers matter you may ask? This brings us to the concept of the Nyquist theorem and Nyquist frequency: For example, the common sample rates of 44.1 KHz, 48 KHz, and 192 KHz refer to 44,100 samples per second 48,000 samples per second and 192,000 samples per second.Ī waveform signal “chopped” into 16 samples Let’s back up a bit to define some basic terminology: What is a sample rate? What is the Nyquist frequency? What is bit depth? If we take a period of one second of a waveform and chop it up into digital samples, the number of “chops” per second is our sample rate. In order to keep digital artifacts from rearing their ugly heads amongst our delivery of crispy, pristine audio, we must consider our application of sample rate conversions and clock sources. In looking at our digital signal flow there are some important concepts to keep in mind when designing a system. The bartender/front-end processor says, “You can order whatever you want, but I’m going to determine when you drink it.” In the modern audio world, we are able to keep our signal chain in the digital realm from the microphone to the loudspeaker longer without hopping back and forth through analog-to-digital (and vice versa) converters. Three digital audio consoles walk into a festival/bar and put in their drink orders.
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