For years people have discussed the pros and cons of onboard sound and sound cards. Both have their advantages so it's a tough call as to which is the better choice. As far as sound quality goes, generally speaking sound cards are better than integrated sound on your motherboard. The drawback is the additional cost. The controversy is whether or not the degree of improved sound is worth that extra cost. What it really comes down to though are people's personal preference and desires. It's probably safe to say that the majority of people choose to go without a sound card and save that extra money, because good sound requires more than just a dedicated sound device.
In order to really have quality sound output you also have to have a nice set of speakers or headphones. It also makes a difference if you listen to regular compressed audio files like mp3 or audio files that haven't been compressed and lost quality. For people who don't do intensive gaming, movie watching or listening to high-quality sound files that haven't been compressed or converted, they're probably better off with onboard sound. It's a bit silly to pay for sound cards that cost $100 $300, just to listen to mp3's through a cheap set of ear buds that came with some random thing you bought. There is a good chance you will hardly even notice the difference between a sound card and onboard in that case.
On the other hand though, pay a hundred or so bucks for a nice sound card and a few hundred bucks on some quality speakers or headphones and the difference should be quite significant. This is especially true for clean audio files that haven't been tampered with. It seems like those two processes always degrade the quality of the file and therefore the output that you hear while playing it. Quality files, though, mixed with good speakers and a sound card together will change your standards on how to pleasure your hearing sense.
So you get some nice speakers and it becomes time to decide whether to go with your onboard sound or a separate card. Which one though? What are the differences between onboard and dedicated sound devices? Is onboard good enough or should I get a sound card? Well the differences are typically signal-to-noise ratio (SNR), the range of frequency response, enhancement and customizable features, quality of I/O (input/output) ports, and API support. Ok what are those?
Signal-to-noise ratio is commonly measured in decibels and is typically seen as a single number rather than an actual ratio. An example would be 100 dB, but you could also assume that it is 100:1 dB. This ratio is a measurement of the quality of the sound. So basically the higher that number is, the better the signal output.
Frequency response just shows us how low the lows can be and how highs the highs can be, which means you want a broad range. Enhancement and customizable features are technologies that allow for anything from karaoke sound effects to simulated surround sound through stereo speakers. I/O ports vary from the common but limited 3.5mm jack to SPDIF optical and coaxial which allow for far superior sound quality. Lastly we mention API's. API's are standards that allow for cross compatibility and many audio enhancement features. Popular ones include Dolby Digital and DTS for hooking up receivers and use of many media programs, and for gaming you're likely to want a card with OpenAL and EAX.
So how do you achieve high-quality sound on a computer? You get a nice set of speakers with a high SNR and a wide frequency response. Then you get a sound card with those two things as well as a nice list of features, API's and ports to really optimize the potential. Lastly you play files that haven't been compressed, converted or distorted in any other way. That combination should have you experiencing sound like you wouldn't believe possible before.