What is Digital Sound?

To understand the basics of how X-Fi works and appreciate the magic behind the sheer numbers, we first need to understand how sound is digitized and to understand THAT, let us first give you an overview of how sound is created and how we hear it.

When an object vibrates, it passes the vibration to the air molecules next to it which then affect the molecules next to them and so on and so forth. This phenomenon continues and eventually the vibration reaches our ears, where it’s transferred through various tiny bones and projected onto the eardrum, the eardrum vibrates and this vibration gets interpreted by the brain as sound.

Now sound has two aspects, the loudness and duration, where duration is obviously how long you can hear the sound.

Objects that vibrate faster give us a higher pitched sound and those that vibrate slowly give us sounds on the lower scale, also, objects that create big vibrations (the molecules are displaced to a larger distance from their positions of rest) produce louder sound. These vibrations can be represented as a graph that looks like a sine or cosine curve as depicted below.

The X-axis (horizontal line) represents time and the Y-axis (line perpendicular to the X-axis, not shown here) represents the amplitude (size of the vibration). A sound at a higher note will have more waves (crests and troughs) for the same length of the X-axis.

For digitization of sound, we use sensitive membranes that work like the setup of your ear bones and the eardrum. The devices are setup so that when the vibrations reach them, they are picked up, thereby causing a production of electrical currents. The voltage of the electric current depends on the amplitude of the vibrations produced. Thus, the sound waves are converted into electronic signals that can then be given the usual binary notation and hence stored digitally. To understand this process further, you need to get familiar with two new terms, Bit Rate and Sampling Rate.

While playing music on your favorite music player, say Winamp, you would’ve probably noted some numbers like 44Khz (audio CDs) and 192kbps. The information given in the Kilo Hertz unit is the sample rate, and the information given in the kbps (Kilo bits per second) unit is the bit-rate.

Lets look at what these two terms really mean. Remember how we had said that the sound gets converted into digital signals? Now what really happens is that the system reads the electric current generated thousands of times a second and gives each of the different voltages (hence amplitudes) a dissimilar binary code. Since the system is taking the readings at specific intervals (how these are decided we will see a bit later), they are similar to screen shots or ‘samples’ taken from a larger set of voltages, and therefore, the process is called "Sampling". CDs have a sampling rate of 44.1Khz that is to say that in one second, the sound has been sampled 44,100 times.

Now lets talk about the bit-rate. The concept of bit-rate is really quite simple. The bit-rate decides how many different voltages the system can sample in one second. Now if you want to comprehend the amount of data we are talking about, remember that a 16-bit mobile phone screen has 65,536 colors (2 to the power of 16), and for audio, we are talking about at least 128,000 bits per second. This is if you aren’t too keen on good quality audio, but if you are then we are looking at least 192,000 bits per second.

So, next time you see someone talking about 44.1Khz at a 128kbps you know that the sound is being sampled 44,1000 times every second and 2 raised to 128,000 different levels of sound are being measured. Obviously, the higher the bit-rate, the more levels of sound you can record.

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