What is digital Audio?
Refers to the reproduction and transmission of sound stored in a digital format. This includes CDs as well as any sound files stored on a computer. In contrast, the telephone system (but not ISDN) is based on an analog representation of sound.
The numeric representation of sound. Typically used as the means for storing sound information in a computer or sampler.
Digital audio is a method of encoding analog audio signals into digital bits of information. Digital information is easy to transmit and record, and can be modified or adjusted quickly without signal degradation. The most common form of digital audio is the compact disc (CD). ...
These are just a few definitions for digital audio. If you are really into the science behind digital audio there are many resources available. My purpose here is to give you a practical look into digital audio and how you can use it to increase your musical experience. So we will start with "How do I get my guitar and my voice into my computer" !
If all you have at this point is a computer with a sound card your only option is to get some 1/4" to 1/8" plug adapter for your guitar and plug into the "Line In" jack, use a cheap microphone with the 1/8" jack or adapter and record using the mixer in your control panel. This is not a recommended method as the quality is very poor. You could try to keep working with your sound card by adding a mixer or pre-amp but you will be wasting your time in my opinion.
If you do not have a computer you can get a stand-alone digital recorder, but why? There are so many resources based on computers and Internet that I am gong to assume you have one.
Get an Audio Interface! In today's world this is the only way to go. This will replace your sound card 100% and give you quality pre-amps as well as line inputs and outputs. Additionally most audio interfaces these days come with a scaled down version of sequencing software like Cubase or Ableton so you can be up and running with one purchase. Some audio interfaces that I have used and recommend are Line 6, Lexicon and M-Audio.
Regardless of which approach you use, after you connect your sources and make noise, the sound will go through a microprocessor called the digital audio converter (DAC) which contains 2 parts. 1) Analog to digital conversion (a/d) and 2) Digital to analog (d/a) conversion. Some call the DAC an ad/da converter. The analog audio Signal goes to the a/d, where it is converted to digital data, then to the CPU, memory, and storage. The stored digital audio (often formatted as a .WAV file) goes back to the memory, CPU, then out the d/a where it is converted back to an analog signal.
The digital audio/MIDI sequencer allows you to record the analog output of your synths, guitars and microphones as digital audio .wav files. Regardless of what method you choose to get audio to the computer it goes through the DAC to computer memory and hard disk. This type of data is correctly called digital audio data. If you record at "CD quality" (which, by the by, is one of the lowest quality recordings you can make now) each second of sound is divided into 44,100 slices. What is this data? It's just numbers. But unlike MIDI data, which is just numbers that represent what notes you played, digital audio data is a numerical representation of the actual soundwave. It "is" the sound, captured in numbers.
Unless you are just a solo guitar and/or vocal you will probably be using midi tracks along with your audio tracks. Drums, bass, keyboard, strings etc. can all start out as midi but before you finish your song for CD production or even MP3, it has to be converted to Audio. To do this you manually connect a cable from your headphone jack into an input jack that is routed to an audio track and set the track to record, hit play and it records your midi. The simpler method is to use Soft Synths. When using soft synths you can bounce your tracks directly to audio in your audio/midi sequencer. consult the user manual for your sequencer for help on this subject.
Equipment: You need a computer that is fairly new, 1.6ghz processor or better, 7200 RPM hard drive recommended (wav files are big so 500 gigs would be good), 2 gigs of memory (more is better). Audio interface (USB 2.0 or firewire), and a midi controller. I use a Line 6 KB37 that contains the audio interface and controller in one unit. You could substitute the controller for an actual synthesizer but I think you have more options using software synths. a microphone is necessary to record vocals but is also recommended for recording acoustic instruments as well.
Software: You need a decent Audio/Midi sequencer like Cakewalk Sonar, Steinberg Cubase, Pro Logic etc. These sequencers may or may not contain good synth samples depending on the version you purchase. a good synth is necessary to take advantage of the great sounds available today.
So, you hook up the midi controller and your audio interface to your computer . You install your sequencing program and select your controller as a midi input and your sound card as an audio output. Your audio inputs are the inputs on your audio interface. They usually consist of microphone inputs with 48volt phantom power, instrument inputs and general line inputs. The outputs from your audio interface could be a headphone jack or line out. You could connect it to a PA or other sound system or just use headphones. Having quality speakers (monitors) is recommended.