A good audio interface is essential to producers for reference and for recording because most stock sound cards will not give you professional sound. Audio interfaces can also greatly expand the possibilities of your recording setup with multiple inputs and outputs, MIDI connection and monitoring options. The options available are sometimes overwhelming so earlier this year we explored some of the devices available on the market by Apogee, Focurrite and Native Instruments. That article can be helpful if you’re looking for details on specific devices. In this article we want to address some of the variables involved in converting sound to digital information so that you can be informed for your studio’s development and educated for your future audio interface purchases

An analog signal, by definition, is A nominally continuous electrical signal that varies in amplitude or frequency in response to changes in sound, light, heat, position, or pressure. Analog can be electrical or mechanical but the key word here is “continuous.” An analog signal path implies a continuous signal in contrast to a digital signal path, which breaks everything into numbers. This is the primary difference between analog and digital sound.

Until the mid 1980′s almost all audio recording devices were analog. That is to say they all used a mechanical or electrical recording methods to capture a continuous waveform. Around this time digital recording started to become affordable and eventually it became the most cost effective way to create music – which is why so many of us use digital devices to create sound today.

Digital to Analog converters are manufactured almost exclusively on integrated circuits (microchips) and the best ones are created by a few companies who specialize in this type of chip architecture. Therefore many audio interfaces share the same  DAC circuits (Cirrus Logic chips show up in many devices.) There are many kinds of DAC circuits, however, and the industry is constantly trying to create better chips.

The next variable to consider is how you will use this device. Is it primarily for playing back music from within the computer? If so you can get away with a fairly cheap interface that will provide great sound. If you want to record outside sources, however, there are many more variables to consider such as how many inputs / outputs you will need and what kinds of signal will be recorded (microphone or line level, for instance.) The more inputs you need, the more expensive the device. Microphone pre amps are also a costly variable that you can avoid if you don’t record vocals. Conversely, if you do record vocals, get an interface with a good preamp or use a mixer in your setup. Other features to consider include MIDI ports, monitor options and optical (digital to digital) ins/outs. Making a list of the things you want to connect will help this process of narrowing down which interface is right for your situation.

FireWire Audio Interfaces use an IEEE 1394 / Firewire type connection cable. Firewire is generally more expensive than USB but offers a faster connection. If your computer has this type of connection it’s a good choice for a low-latency, high-bandwidth, plug-and-play setup. This connection was developed by Apple and was simultaneously supported by Sony (who calls it IEEE 1394) so it’s become a highly-supported protocol for connecting digital devices to computers. The speed of Firewire is similar to that of USB 2.0 but Firewire handles heavy data traffic much more efficiently. Firewire is intended for devices working with a lot more data (things like camcorders, DVD players and digital audio equipment.) When using this protocol for Audio Interfaces the plug-and-play operation combined with peer-to-peer connectivity make this format ideal for setup and easy expansion. Firewire audio interfaces tend to have more inputs/outputs and offer a higher sample rate than many of their USB-based peers.

PCI Audio Interfaces use an expansion card that physically installs into your computer (usually a tower-based PC) and uses cables or a break out box to connect to your audio devices. The advantage of this format is speed and the ability to run multiple inputs and outputs. This format does require opening up your computer and installing physical hardware. This format is also primarily for tower-based computer configurations (so it won’t work with your laptop or iMac.) PCI based audio interfaces can provide great stability for data transfer but the setup for these is usually a lot more complicated.

One last type of audio interface uses the laptop-specific Cardbus or PCM-CIA connection. There aren’t many of these on the market but a few companies (such as Echo and RME) do produce really nice audio interfaces in this format. For mobile users that don’t want an external box this can be a compact and stable way to connect to your laptop.