What is... a sound card?
A little of history
The PC (Personal computer) was not thought in the beginning to handle sound, except for this reminiscence that in any computers does not settle already (or it is disconnected) called "internal loudspeaker" or "PC Speaker".
This whistle that we hear when we start the computer has been for many years the only sound that has expressed the PC. In the beginning, the loudspeaker was serving to communicate errors to the user, since most of times, the computer had to remain alone working (the first computers were very slow, and the users have right to have an afternoon snack).
But there entered scene the software that of course MORE has made the computers evolve from his appearance: the video games. Probably the programmers thought: "Would not it be wonderful that the muñequitos those were expressing sounds? Would not a sound-track be even more incredible?" For the one who has never played a game with music or sound for the loudspeaker of the PC, which proves this OLD game, probably of the first ones that were programmed for the compatible ones. (Certainly, we have not even idea of how it leaves of him, as it is not with Ctrl+Alt+Supr...)
If you play "Alley Cat" you will verify that the sound is not anything of another world (although I have heard real MUSICAL MARVELS in the loudspeaker of the PC, things that he had never believed). Nevertheless, a little later, in full revolution of the digital music (the digital musical instruments were beginning becoming popular) there appeared on the market of the compatible ones a card that revolutionized it, the sound card SoundBlaster.
Finally it was possible to convert analogical sound to digitalis to keep it in our PC, and also to turn the digital sound that exists in our PC to analogical and to be able to listen to it for our loudspeakers. Later they appeared the rest: SoundBlaster PRO, SoundBlaster 16, Gravis, AWE 32, AWE 64, MAXI SOUND... all more or less compatible ones with the supersuccessful original SoundBlaster, which turned into an authentic standard.
The computers had (they keep on having) a "problem", they can only work with digital information (more specifically binary, 0s and 1s), therefore when we connect a few loudspeakers to our sound card, there is someone who transforms this digital information in analogical so that our loudspeaker understands them. Of that one entrusts the DAC (digital - Analogical Converter,).
And I suppose that it will have deduced the whole world why it serves the ADC analogical - Digital (Converter); really, when we record from an external source (for example from our musical team), we will have to transform this analogical information that come for the cable in digital samples that we could store on our hard disk.
But it can to someone happen that he needs to reproduce sound, to treat it at the same time with an external source and to record it again. Or simply to reproduce and to record at the same time. This characteristic is known as "fullduplex" and must be present in any moderately decent sound card (I believe that at present it it is already in practically all). For it, two converters ADC-DAC must work of separated form.
Nothing of 32, 64, 128 and 256 bits. The sound cards (except very rare professional exceptions) take the sound samples to 16 bits (although his name is SoundBlaster 128 PCI or MaxiSound 64). This has taken to trick more of one (and of two) on having believed that his sound card was working with more bits than its own processor (but it is a question of the number of voices, which is another completely different topic). These bits come to define the position of the loudspeaker. What means this? We are going to explain it.
To express sounds, the loudspeakers move beating. These blows do that the air that surrounds us vibrates, and our ears receive these vibrations and transform them into nervous impulses that go to our brain... (good, this is already not a thing of the computers). Well, we will have to indicate him to the loudspeaker where it must "beat". For it simply we will send to him a position (in this case a number). Well, all the more positions let's be able to represent, the sound will be better. And all the more bits let's have, more positions we will be able to represent (simple: truth?).
The difference is valuable. And I suppose that the whole world can do to himself an idea of what will sound better...
Are more bits necessary? At first not; nevertheless, as in everything, when the ADC is not excessively good, the last caught bits have information that is not too trustworthy. This means that if we can work with a major bits fan (20 or more), although we lose quality the final sound will keep on being equal of good.
44,1 KHz means CD quality
We are going to explain this. The sound cards simply transform a continuous sign (the sound is something continuous, it does not go to t-r-o-z-o-s) in the discreet one (although it it does not seem). We explain the "discreet" word: that happens at certain time intervals.
Let's see an example graph.
In the drawing you appreciate a continuous line, which represents a sound. Nevertheless, in fact when we receive it with our sound card we cannot capture the WHOLE wave, we will capture simply a series of points (those that are marked), a point from time to time, that is to say, a sampling of the information with a certain frequency; the wave that we will have left will be of the following style:
You can imagine that if instead of 44KHz we use 22KHz, in fact we will capture half of positions:
The sound degrades itself quickly.
The conclusion of this exercise of drawing to raised hand is very simple: all that more resolution let's have, the representation of the sound will be better in our computer. Some cards incorporate interpolation, by means of which the peaks are smoothed and it is possible to obtain a wave more similar to original again, improving, according to the manufacturers, the sound quality. Really, I still do not meet any person who has been capable of distinguishing between two sounds (with and without interpolation).
And porqué exactly 44’1KHz? For the same motive for which the VHS expresses 24 images per second: if the human eye is capable of recognizing approximately 30 images as much per second, it would be a waste of means (and money) to express 100 images per second, for the simple fact of which we would not notice the difference. In the same way, the human ear is capable of recognizing approximately 44.000 sounds every second (or, it receives the sound with this frequency), with what the use of a major sampling has not any sense (at first).
All the domestic sound cards can work with a resolution of 44’1KHz, and many even do it to 48KHz. The semiprofessional ones work mostly with those 48KHz and someone even with 50KHz. The professionals come close to 100KHz.
The use of this extended sampling owes to the same motive for which some cards use more of 16bits for every sample: if the game information is not sufficiently faithful or later we go to dedicate to modifying the sound, we will lose quality, so all that we have more quality in the beginning, better results we will obtain in the end, it is better to work with a confidence margin.