About USB Audio Interfaces

One of the better things to happen in the music technology industry is the proliferation of USB audio interfaces. The devices bring many of the benefits that professional recording establishments have enjoyed for decades but with a price tag that does not require a second mortgage or a business loan to acquire.

Generally speaking, USB audio interfaces come in two categories: stereo and multichannel devices. Professional and consumer versions of each are available with prices ranging from $50 to $10,000 or more.

Types

Most USB audio interfaces are USB 1.0 and USB 2.0 compatible, so you should have no problem getting a device to work with any computer manufactured in the last 5 years. A USB audio interface attaches to the computer with a standard USB connector and to the device itself with any number of other connectors, ranging from proprietary connections to standardized connections.

Features

USB 2.0 can handle bandwidth of 480 MB/second. To put this into perspective, 24 bit/192 khz audio--the highest bandwidth in commercial use--uses approximately 10 MB/second per track of audio. So, a stereo recording would take approximately 20 MB/second or 5 percent of the possible USB 2.0 bandwidth. This large amount of bandwidth available allows for USB audio interfaces to accommodate just about any recording or playback scenario imaginable.

Most USB devices can be connected in a chain with another USB cable. Special software is often necessary and provided by the manufacturer for these USB devices. In some cases, a single USB port on a computer may support up to 48 channels of audio at one time. The primary limitations to the number of available audio channels are the physical limitations of the actual USB device and the processing power of the computer.

Size

USB devices range in size from 3" X 1" to multi-rack units. The differences in sizes are due to the types of connectors available. The smaller USB devices may only have a single 1/8-inch input and one 1/8-inch output port, allowing the unit to be extremely small. On the other end of the spectrum are USB devices that have up to 12 XLR type connectors for inputs and eight TRS (tip-ring-sleeve) or 1/4-inch connectors.

Considerations

USB audio interfaces certainly have many advantages, but a few disadvantages are worth noting as well. The primary advantages include the fact that many USB audio interfaces can be powered by the USB bus making the devices useful with laptops and also that the device is independent of the computer tower, which reduces the potential for additional noise being introduced. An additional benefit includes the low price when compared to PCI-based audio interfaces

Some of the disadvantages of USB audio interfaces are that the digital audio converters (DACs) are often inexpensive and noisy that and the consumer units can often only include 1/8-inch adapter connectors, which means specialized cabling and equipment may be necessary to interface with professional equipment.

Misconceptions

The biggest misconception as it relates to USB audio devices is that of bandwidth. Most people are also concerned with two factors when considering using a USB audio device to record: the audio quality and the number of channels available.

Audio quality is effected by the type of microphones, use of the microphones, and level of the audio signal to a much greater extent than the USB audio device type. If the audio signal is at the appropriate level, most USB audio devices do little to change the sound of the audio--the signal is simply converted from analog to a digital signal.

The number of channels available is first limited by the USB audio device. A stereo USB audio device will only be capable of recording two channels at a time. Most people are concerned with larger USB audio devices which have eight or more channels. Even at high resolution audio--24 bit/192khz--an eight-channel USB audio device will be using around 50 percent of the capacity of a USB port.