Finding the most suitable USB audio interface for a particular application will require careful consideration. USB audio interfaces can be very complex devices, which can make them difficult to compare at the time of purchase. It is worth remembering that a USB audio interface will often form the heart of a music recording solution. Therefore, it is worth taking the time to fully research the differences between the various models on offer. This will ensure that the device purchased will meet all current and future requirements.
USB Audio Interface Development
Modern personal computers were initially developed to be used solely as business machines and so were not designed for the application of digital recording. As the multimedia capabilities of these machines increased, sound cards were fitted. These sound cards were in turn developed for computer gaming and movie watching applications. For this reason, they initially lacked the power, speed and connectivity required to allow the computer to be used for recording professional-quality music. In response to demand from the music industry, sound cards were created which were capable of being used in this role. At the same time, laptop computers underwent a surge in popularity. These factors, together with the demand for cards with ever more numerous and varied connectivity, resulted in the production of the very first external audio interfaces. Modern USB audio interfaces are a continuation of this development. They vary from simple two channel devices, for recording accompanied vocals, to models with enough power to allow them to be used as the basis for a professional home recording studio.
Requirement for a USB Audio Interface
In its simplest terms, a USB audio interface is an analogue to digital converter. It takes the analogue single from the recording microphones and converts this to digital, enabling it to be processed by a computer. The computer may itself have a sound card cable of doing this job, but a dedicated audio interface will be able perform the task to a professional standard, without introducing any errors and with no detectable latency.
Choosing a USB Audio Interface
When choosing a USB audio interface, consideration must be given to both current and future recording needs. Underestimating the required specification can make it necessary to upgrade the interface prematurely, while overestimating can mean paying for functionality that is never used.
When considering input and output requirements it is important to fully consider all the different communication pathways, whether analogue, digital or optical. In particular, optical pathways need extra consideration as they are capable of carrying more than one channel of digital information. Usefully employing optical pathways can effectively free up connectivity elsewhere.
Number of Inputs
The most important decision when buying a USB audio interface is choosing the number of inputs. It is worth making a list of what hardware will be connected to the device and noting the connectivity of that hardware. A similar list should then be compiled for any possible future hardware purchases. Any other factors which could put pressure on the number of inputs should also be considered at this point, such as potential future increases in instruments or musicians. The above lists should give a good indication of the number of inputs the USB audio interface will require and the different types of connectivity that it must support. Compiling these lists should ensure both current and future needs will be met by the new device.
Number of outputs
Current and future audio output requirements should also be considered using the method described above. This should encompass not just headphone and monitor requirements, but also any analogue processing equipment through which the mix might be sent and retrieved. There are USB audio interfaces with enough outputs to meet the requirements of any recording situation. For example, eight output port models are available which are capable of supporting all current surround sound formats.
The end quality of the output from the USB audio interface will be determined by the digital to audio converters within it. The two terms that describe the quality of these converters are bit depth and sample rate.
The bit depth determines the theoretical maximum dynamic range of the audio data. A single increment in the quoted bit depth means a corresponding dynamic range increase of 6 decibels. Therefore, relatively small differences in bit depth can have a dramatic effect on the dynamic range of the audio output. A 24 bit USB audio interface will therefore capture quieter signals with greater accuracy than a 16 bit device.
The sample rate of a USB audio interface is the number of digital snapshots of the analogue signal it is capable of taking in a given time. The frequency response of the device is the highest frequency that it can record and play and this normally approximates to around half the sample rate. A device that is recording at a sample rate of 44.1 kHz will produce output of a comparable quality to most pre-recorded compact discs. The importance of bit depth and sample rate will depend on the intended application of the USB audio interface. While the superior headroom provided by a higher bit depth is almost universally appealing, recording at higher sample rates can have some drawbacks. File sizes will increase dramatically, particularly at the highest sample rates, which can mean a reduction in the number of tracks that can be offered.
There are three significant compatibility issues worth checking prior to purchasing a USB audio interface.
The device should be checked to see that it is compatible with the operating system of the computer with which it will interface. Most USB audio interfaces on the market today are cross platform, meaning that they are compatible with both Microsoft and Apple operating systems. It should be determined that there is a suitable method of physical connection between the computer and the audio interface. Almost all new computers and audio interfaces will possess a USB 2.0 connection which will provide the desired speed and the convenience of plug and play. If both devices possess Firewire 800 ports, this will provide an equally useful alternative method of connection. The last items to check for compatibility issues are the USB audio interface and the audio software with which it is intended to communicate. It is unusual for audio software not to support a particular USB audio device, but an individual software application may work better with some devices than others. USB audio devices are sometimes bundled with a sample of compatible audio software, so it is worth checking whether this is the case.
Another important consideration when buying a USB audio interface is how portable it needs to be. If the device will never leave the home recording studio, then the weight and footprint of the device are not important factors. However, if the audio interface is to be used at various locations, for example for recording live performances, then it is worth comparing the physical dimensions and the robustness of any interfaces that are under consideration. A rack mountable USB audio interface can be a good choice for a more mobile application. Flight cases are widely available for transporting rack mounted devices, allowing them to be moved about in a safe and convenient manner.
Find USB Audio Interfaces on eBay
To buy USB audio interfaces, go to the eBay homepage. Begin by opening the All Categories tab and then clicking on the link for Musical Instruments, followed by Pro Audio Equipment. Next, click on Audio/MIDI Interfaces and then USB Audio Interface. The search can be further refined using the options on the left of the page. It is possible, for example, to view only the USB audio interfaces which fall within a particular budget. These options can also be used to narrow the search to only include the particular types or brands of USB audio interface that are of interest. Another alternative is to enter specific terms into the search bar at the top of any eBay page to locate a particular kind of USB audio interface. For example, to find an unused Roland USB audio interface, simply type "Roland USB audio interface new" into the search field.
Direct comparison between USB audio interfaces is not a particularly easy task, as they can be fairly complex devices. However, they are a key component in a home music recording set up and so it is worth taking the time to do some research. Creating a current and future requirements specification is a good first step. This can then be used to create a shortlist of potential devices which will be able to perform the required tasks for the given recording application. Careful thought should be given to input and output connectivity, sample quality and portability, as well as fully investigating potential compatibility issues. With due consideration, the purchase of a new USB audio interface can provide a home recording solution that will give long-lasting service and meet all expectations.