A USB Audio Interface allows the connection of microphones, guitars and other electric and electronic instruments to a computer via a USB port, allowing voices, music or music data to be recorded on the computer using either recording software or MIDI sequencing software. These interfaces also allow recorded material to be played back from the computer via the interface, for monitoring, recording/playback or multitracking purposes. Recent years have seen the growth of personal recording, as opposed to the traditional method of recording musicians in a studio built for the purpose. Personal computers have become more powerful, disk-based storage has become cheaper, music recording and sequencing software has seen considerable development, and all these factors have led to a change in the landscape of recording and music production, especially in the realm of electronic music, where many artists produce finished work single-handed, without venturing outside of their homes.
USB, Firewire, and PCI
There are a number of methods by which external audio devices can be linked to a computer. Connecting via USB is the most common and most economical, since every modern computer is fitted with USB ports. Firewire and PCI interfaces use different physical connections and communication protocols, and are outwith the scope of this article.
Choosing a USB Audio Interface
The primary consideration is likely to be that of how many inputs and outputs are needed, and the player or producer should assess this on the basis of their current needs, with some thought to future projects and expansion. Some thought also needs to be given to the type of inputs required, considering whether the interface will be used with microphones, electric instruments such as guitars, or electronic instruments and devices such as keyboards, synthesisers, or sequencers. Line-level inputs can be used for connecting equipment such as mixing desks, CD players, synthesizers, and other keyboards. Microphone inputs are designed purely for use with microphones, which work on much lower signal levels, and which sometimes require phantom power to be provided from the device they are plugged into, such as the interfaces discussed here. Some thought should be given to the flexibility of the inputs, if there is any, determining whether or not the inputs have been designed with one purpose in mind, or if they are switchable according to the type of source in use – these are commonly referred to as ‘versatile’ inputs. A player or producer working exclusively with a solo instrument such as a piano will be unlikely to need an interface featuring multiple inputs, and is likely to find a basic 2-channel model to be sufficient. Those working with larger acoustic ensembles are likely to need more – eight, or sixteen, perhaps. Those working with keyboards, other electronic instruments or ensembles using a combination of the same, should also consider the MIDI capabilities of the interface (see below), and whether or not any kind of sequencing software will be in use. The most basic interfaces will have a standard stereo pair of outputs for monitoring and playback in stereo, and some will have headphone socketry for the same purpose. The more advanced interfaces could have multiple outputs with different configurations for monitoring, or could have capabilities beyond basic stereo, possibly with multiple outputs for surround-sound work. Some consideration should also be given to the interface’s digital capability, should it be required to connect to other digital devices, such as digital recorders. S/PDIF (Sony/Philips Digital InterFace) uses either coaxial phono or Toslink optical connectors, and is used for making connections to digital recorders, CD players, effects units with similar digital interfaces, as well as some keyboards and/or synthesisers with digital outputs. Although some audio interfaces have both coaxial and optical connectors, it’s not crucial that they do, as format converters are available to convert coaxial to optical and vice versa. It is necessary to consider whether or not high-resolution digital work will be required. Commercial studios are often working with digital resolutions well above that of a standard CD, with sampling rates extending to 96kHz and beyond, and a bit depth of 24 bits becoming the norm. With this in mind, anyone purchasing an audio interface should consider their future plans and the pace of progress in this vein.
Some interfaces offer the capability to connect to ADAT (Alesis Digital Audio Tape) recorders using Toslink optical connectors supporting up to eight simultaneous digital audio channels. A typical use for these would be to partner up an ADAT multitrack recorder with an interface and computer for multitrack recording flexibility.
MIDI (Musical Instrument Digital Interface) is a method of sending musical data between electronic instruments (usually keyboards) and other devices, such as sequencers, sound modules and recorders. Keyboards and controllers can be used to generate sounds from samplers and sound modules, and sequencers can be used to control keyboards and sound modules. In the context examined here, a player or producer could consider a USB interface that handles MIDI data as well as pure audio signals, depending on their requirements. A specialised electronic musician would certainly put this high on their list of priorities, but it’s unlikely to be a requirement for anyone working with purely acoustic ensembles. Anyone working with a mixture of acoustic and electronic instruments should probably consider an interface that includes MIDI functionality, for added flexibility.
Extras and Other Facilities
Many audio interfaces incorporate DSP (Digital Signal Processing) for the on-board mixing functions, and recent developments have seen interfaces incorporating advanced DSP functions such as audio effects and bass management for surround systems. Many performers find headphone monitoring of their performance easier without any latency (delay) between their singing and their monitor mix, and may also need effects during performance. Handling these aspects of processing within the interface, rather than sending them via the computer software, leads to better performance.
Fortunately, USB audio interfaces have, in common with many other electronic devices, few moving parts, and, therefore, there is little to go wrong. Only in the most extreme cases of abuse by prior owners or users is there likely to be any damage to the internal electronics. Some USB audio interfaces are freestanding, others are designed for rack mounting, and depending on previous usage, there may be marking to the external casework, either from general wear and tear, or from insertion and removal to and from equipment racks. In most cases, any case damage is likely to be cosmetic, and unlikely to affect the core operation of the unit. Occasionally, plugs, sockets, and controls can be damaged, or affected by the build up of dust and dirt. In most cases, physical damage can be simply remedied by replacement of the sockets concerned, and contamination by dust and dirt can be resolved by the use of switch cleaning fluid, compressed air and the like. If in doubt, remember to ask the seller regarding the condition of the used USB audio interface.
Finding Used USB Audio Interfaces on eBay
From the eBay homepage, select Browse by Category, and expand the category page to show All Categories. From there, select Musical Instruments, and Pro Audio Equipment. Select from the left-hand panel Audio/MIDI Interfaces, and again from the left-hand panel, the type – USB Audio Interface, further narrowing this to Used items.
USB audio interfaces are a cost-efficient method of linking a computer to external audio devices and musical instruments. In the main, they are not particularly susceptible to damage, and an online purchase of one which bears little or no physical damage is likely to be a safe purchase. The purchaser should determine their current requirements, make reasonable allowance for any future changes or additions to their current setup, and purchase the interface which matches their needs.