Q. What hardware do I need to make professional recordings?

See the companion article on digital recording software

When you want to record music and get a good sounding result, you will want better quality and more flexible audio interfaces than the Mic jack on your computer.  Getting the audio interface outside of the noisy internal electronic environment of the computer’s case, and using higher quality Analog to Digital (A/D) and D/A converter chips both help record a better sound.

For single channel recording, the cheapest entry level would be products like
Griffin iMic $48
Alesis LineLink $68 and MicLink $68
Blue Icicle $72
Guitar-specific interfaces and software
USB microphones

These solutions will accommodate a single player / input at a time, and could be enough for podcasting, songwriting/scratch recording and narration work.

As soon as you need to record multiple players, microphones or instruments, or get to a more professional quality of recording, you would look for a multiple-input USB 2.0 or Firewire audio interface. Digital Audio Interfaces are available from these companies:

Alesis
Edirol
Creative / Emu
Focusrite
M-Audio
Presonus
Tascam
TC Electronics
RME
Yamaha
and others

Some of the interfaces incorporate mixers, so you can use them for mixing live sound at the same time as recording the performance. Be careful when evaluating interfaces, don’t assume a high number of inputs means you’ll be able to plug in a dozen microphones, because the input and output count often includes line and digital inputs – so for example an 18 input interface may have only four mic inputs and two stereo line inputs, plus 10 digital inputs (8 in TDIF format and 2 in S/PDIF format)

Audio hardware often comes bundled with software – Digital Audio Workstation (DAW) recording software, instruments, samples, effects and loops.  Often these are trial versions or junior versions of the full software, so read and understand exactly what you are getting with the bundle.

If you want to use a professional condenser microphone, look for an interface that has at least one balanced XLR mic input, with phantom power.  Many condenser microphones require the  preamp, mixer or interface to provide 48V power.

Hit the library and read up in back issues of magazines, or subscribe – they have hundreds of how-to articles and comparative reviews of software, mics and interfaces.

Sound on Sound, from the UK, probably the best how-to magazine on project studio recording.
Electronic Musician /EQ (these two magazines recently merged) lots of coverage of recording techniques and software.
Recording, good general magazine on recording
Keyboard focused on keyboards, but covers software and hardware recording articles as well
FutureMusic from the UK, focuses on electronic modern popular and dance music
Computer Music from the UK. Often comes with free software on the cover CD.
MIX oriented more toward professional studio recording and live sound

There are guitar-specific programs and interfaces for recording electric guitar, and plug-in effects, software instruments, sample libraries and loop libraries which integrate with your DAW for constructing recordings.

Pay attention to your recording environment as well – if you are recording acoustic instruments or voice, the results are only going to be as good as your room sounds. A crummy sound in a room cannot be massaged into a great recording, Get the acoustic sound happening first.  I like the Studio Rescue article series in Sound on Sound magazine for practical tips.

See the companion article on digital recording software
Look for an upcoming companion article on mastering software
Look for upcoming articles on microphones and on compressors and preamps