The Linux-Based Recording Studio
As you can imagine, your choices are endless. You conceivably could choose any combination, such as converting analog to digital with the sound card while converting digital to analog outside, or vice versa. It's a bit easier, though, to pick one place to do all your conversions, either in the sound card or somewhere else. If you simplify it this way, your decision comes down to whether to have an external mixer.
In the simplest configuration, say if you were using a consumer sound card with only one stereo output, you'd mix entirely in the computer and not think much about the ADC and DAC being done in the sound card. You would then have no external mixer (see the Preamps section below).
If you do have an external mixer, you're either using an analog mixer or a digital mixer. In either case, you need a professional sound card that can separate channels, as opposed to a consumer card that outputs only one stereo mix, requiring you to mix inside the computer.
If using an analog mixer, your DAC and ADC happen in your sound card. Therefore, you need a sound card or sound card/breakout box that has analog inputs and outputs, such as RME's PCI cardbus and Multiface combination card. There is a nice primer on this card on the LJ Web site (see the on-line Resources).
If you choose a digital mixer, your DAC and ADC happens in the mixer itself. You therefore need a sound card that has digital inputs and outputs that are compatible with your mixer. In my case, this is RME's HDSP 9652.
Many digital mixers have built-in effects and processing, including reverb, compression and noise gates, as do many software packages. Few analog mixers offer such features, so if you're doing traditional analog mixing, you might spend more on outboard effects and processing. There still are plenty of reasons to use these tools if you've got the money, but on a budget, I recommend a digital mixer.
A few questions to ask about potential sound cards:
Is it noisy?
Does it have the ability to record while playing back (duplex mode)?
How many channels can it play back at once?
How many channels can it record at once?
What kind of physical I/O ports does it have?
Does it have built-in MIDI?
Is there a Linux driver for it?
If you're recording acoustic sources, such as voice or drums, you need microphones. Your budget and what you're recording influence your decisions here. For example, if you have a medium to large budget and need to record an acoustic guitar and singer, I might recommend two AKG 414s (about $1,000 US each). If you need to record pristine vocal tracks and have a large budget, I might recommend one Neumann U87 (about $3,000 US). Or, maybe you have a small budget but still need to record vocals and an electric guitar amp. Then I might go with a pair of Shure SM58s, about $100 US each. Of course, if you never record acoustic sources and only use synths plugged in directly, you don't need microphones or preamps.
The signal from a microphone needs to be amplified before it is loud enough to record or broadcast properly. If you plug a computer microphone in to the microphone input of a consumer sound card, you're using a preamp, and you should get a loud enough signal. If you try plugging in to the line input, you barely get anything. Professional sound cards don't have 1/8" microphone inputs and assume you have outboard preamps.
The question is whether to use standalone preamps or the preamps built into a mixer. For most, the preamps in almost any mixer are sufficient. The only reasons not to use the mixer's preamps are if you don't have a mixer, you need more at once than your mixer has or you have aesthetic reasons to use a standalone.
The need for preamps is a good case for having an external mixer, because having a professional sound card with multiple analog inputs, no mixer and a bunch of outboard preamps usually is more costly and less flexible than having a mixer.
To listen, you can use anything you please, from computer speakers to headphones to a home stereo speaker/amp combination to studio reference monitors. There is, however, a distinction between speakers and monitors. A speaker is designed to enhance the sound of a recording, and a monitor is designed to give an accurate, uncolored representation. If you want to do accurate work, you need monitors.
Studio monitors come in a variety of flavors. The major thing you need to know is whether a set is powered. If it isn't, you need a power amp, just as if you were using a set of home stereo speakers. Replacing your regular speakers with studio monitors and connecting to your existing amp is easy.