Analog to Digital (A/D input) and Digital to Analog (D/A output) converters are pieces of hardware which manage the Input and Output (I/O) in your audio interface. Even the most high-end Macs or personal computers use very basic, low-quality converters, which are the same ones incorporated into cheap computer systems.
 
You can upgrade your audio interface by choosing from a wide range of stand-alone interfaces available in the market. These outboard interfaces typically allow for more I/Os, improved A/D/A conversions, and additional features such as volume knobs. The hardware unit that has I/O jacks is also known as the ‘interface’, ‘breakout box’, or simply, the ‘I/O’. The archaic label ‘soundcard’ conventionally refers to circuit boards that needed to be affixed to the PCI slot of a computer. Many of the computers sold today do not have slots for PCI, thus rendering PCI soundcards useless. A FireWire or USB will solve the interface issue, as it takes the place of the soundcard.
 
A USB or FireWire interface gives you the flexibility of ‘hot-swapping’, as well as being able to transfer files to notebook computers. The slower USB 1.1, which works at 12 MB per second, may not work properly under the load of several channels, while FireWire technology operates at 400 MB per second. FireWire 800 is much faster at 800 MB per second, and USB 2 is more efficient than its previous version at 480 MB per second. PCI may operate at decent speeds, but the technology is inconvenient to use.
 
Your operating system must be compatible with the interface you choose. Your software must be able to identify the presence of the interface. Many Macs have USB or USB 2, and FireWire (IEEE 1394). PCs have either USB or USB 2 as well as FireWire. FireWire 800 is just now starting to be introduced and is not very widespread in its adaptation yet.
 
Regardless of the interface you have, the right cable is integral to your audio interface. The cable will connect your computer to the amplifier. Many amplifiers for consumer electronics utilize RCA jacks. Your output jack may be the round 1/8-inch mini – in this case, purchase a 1/8-inch-to-RCA adapter. Professional variants use XLR jacks with three pins.
 
If you do not have an amplifier, or it is located at a greater distance than cable length can reach, look for speakers that are USB-powered, like SoundSticks from Harman Kardon. These speakers attach using the USB port and work without an amplifier. Bose and Polk Audio also have non-USB speakers. CRT monitors require you to employ shielded speakers. AirFoil sends the audio to Apple’s Airport Express, for use with Mac computers.
 
Be sure to inspect your interface, and the number of physical inputs and outputs that it has for analog. Most companies state that their interfaces have so-and-so number of inputs, although some of these are digital, including ADAT and S/PDIF. ADAT inputs are necessary for additional mic pre-amps. To this, ADAT-output external mic pre-amps may be added. You can choose from the ADAT-interfaced Focusrite OctoPre, or Presonus Digimax. If you wish to do large amounts of audio recording for whatever purpose, consider acquiring more hard drive storage, plus a reliable backup system.