Digital Computers and Digitization
We all use digital computers, but do we actually understand what they do and how they work? Since they are ubiquitous in our lives, we often just assume things without actually understanding them. The most common usage of digital computers is what you are doing now, reading digital text on a computer. This is perfect application for a digital computer, because it is 100% composed of discreet numbers, some of which get displayed as characters, others are added together to produce higher level math functions to keep track of things.
But digital computers do so much more than just text and numbers. In fact, many things in life have been digitized, much to the detriment of many traditional industries. Computers completely changed music, video and almost anything else that can be converted to ones and zeros and then converted back into a close enough approximation of the original.
Living In The Analog World
We live in an analog world. You could say the analog world is actually a wave based world. What we see and hear are actually waves our brain turns into vision and hearing. Light is just a mass of different wave lengths arriving at our eyes. Sound is just the movement of air in waves hitting our eardrums, and we interpret that as sound.
Video, film, and photographs are just representation of light at a specific time. Music and sound are just movement of air over time. Both analog. But computers are digital. They store only ones and zeros, or on and off, or even high and low. How then can we convert our analog waves of light and air into a digital computer and have it come back out again in something we can recognize? After all, digital computers are just that, digital, not analog. They don’t store or compute based on wave forms (unlike analog computers, which we are not discussing here), they use numbers, more specifically, ones and zeros. Do how do we get from one and zero to music we listen to on our computers?
Enter Digitization
The answer, as so often in computers, is to break up the problem into smaller chunks. This is called sampling where the computer takes a very short duration snap shot of the value of the wave form. For photos and video, we have millions of tiny sensors that record the color and intensity of the light at the moment of exposure, and for audio, we record the amplitude of the audio at the time we sample it. We then store that number and repeat the process until we want to stop recording. Video also repeats the process, but for all the millions of sensors in the frame.
The distance between samples is called resolution. The more times we sample audio or the more pixels (sensors) we have in the frame, the higher the resolution of the sampled wave forms.
Why resolution makes a difference
Most people understand resolution in photographs in terms of the number of megapixels advertised for cameras. The higher the number of pixels, the more detailed the photographs become. Most of us will remember the first digital camera or cell phone cameras. Often the resolution was 1 megapixel or less. While these low res images worked, they did not enlarge very well, becoming fuzzy when you tried to zoom in or show on a larger monitor rather then your phone or even the screen on the camera.
But why does a lower sampling rate (say one megapixel vs 20 megapixels) make a difference in how clear the photograph is? Simply because the computer does not know what to put between samples when the samples become further apart. And by enlarging a digital photograph, you are separating the pixels and the computer has to guess what the missing samples might look like. So it employs various techniques that all boil down to educated guess work.
The solution for this is to increase your sampling rate (megapixels) to get a clearer image. The more samples, the less guessing the computer has to do when reproducing the image, and the clearer the image.
While resolution is easy to understand for images, more resolution means clearer images, what does it mean for digital audio? After all, humans can’t really hear any frequency over 20 kHz (20,000 cycles a second). The Nyquist–Shannon sampling theorem says that the CD sampling rate of 44.1k samples a second is sufficient to reproduce all frequencies that humans can hear. But does that mean that a higher sampling rate is wasted on human hearing? Just like images, higher sampling rates in audio mean clearer audio. Since there are more samples, the recreated wave form is closer to the original. Have you ever heard audio in the distance, like a band playing, or a DJ? You almost instantly know if the source is live or recorded. Why? Simply more detail in the waves reaching your ears. Live audio does not go through the digital process, it simple goes through analog amps that might add some noise, but the wave forms are not altered by the electronics. This results in a clearer and more open sound.
Another factor in digital audio is the bit depth or size of each sample. A CD has a 16 bit depth, meaning 16 bits are saved for every sample. The bit depth is directly related to the dynamic range the CD can reproduce. The larger the number of the sample, the louder the wave form is at that point. This is referred to as the dynamic range of the recording. CDs can reproduce about 100 dB of dynamic range, which is well below the limits of human hearing of 140 dB. Higher sampling rates are generally recorded at 24 or 32 bits, meaning they can reproduce over 140 dB of range for a 24 bit recording, and even more for 32 bits.
So both the sampling rate and sample size affect how accurately the original sound can be reproduced.
So what does higher resolution mean in audio?
For photos and video, we know a higher sampling rate means a clearer image or video, but what does that mean for digital audio? Exactly the same thing! Sampling rates above the standard 44.1k of CD’s and 48k of basic video means the sound is clearer. It has more definition and less guessing. I often think of higher sampling rates as lifting the fog of the recording. Things are cleaner, sound seems even more real. You start to notice things like fingers on the strings and fretboard of a string instrument. Higher audio sampling rates are all about recreating the recorded sound more accurately.
But what about Frequency Response?
Frequency response, or what range of frequencies can be reproduced by by a recording system, is an artifact of early high fidelity system marketing. Years ago, playback systems were not great and frequency response was something that could be measured, and therefore marketed. In the digital age, frequency response is a solved issue. But resolution was initially not. People complained (and still do) about CD quality audio. And while mastering techniques have improved, CD’s can simply not reproduce the dynamics of sound humans can hear. High resolution audio can, just like higher resolution photos and video.
Does is make a difference?
And this is the big question. Obviously on your phone, you are not going the hear much difference in sampling rates for audio, photos or videos, because the screens and speakers they get reproduced on simply don’t have number of pixels or fidelity you need for a full quality reproduction. But once you depart from small devices and into larger displays and speakers, you start to notice the lack of resolution in lower sampling rates. Most modern DVD and Blu-ray units can decode 192k/24 bit audio. Amplifiers and speakers are basically analog, so yes, you can hear the difference if you know what you are looking or listening for. Does it matter to you? You will have to make that decision yourself once you try higher res media, but to say it does not matter, is more a reflection on your ability to understand digitization rather than the technology itself.
