Interface Setup
An audio interface is a device that is used to transfer audio streams (usually analog) to and from a computer, allowing recording and playback for DAW software. They typically include microphone, instrument-level, RCA, SPDIF, and AES-EBU inputs, as well as monitor, headphone, and auxiliary/line-out outputs. Often they will interface MIDI in addition to audio.
Interfaces vary in form factors and how they connect to the computer. Early interfaces were PCI cards that had to be inserted into the computer's motherboard. Modern ones may use a PCI or PCI-e card, or use USB 2, USB 3, or a Firewire connection. Some early interfaces consisted of nothing but a PCI card and a break out cable that split into various jacks to connect to audio cables - all the controls for the inputs were controlled via software. Most interfaces nowadays consist of a hardware box meant to either sit on a desktop or live in a rack - the box provides various controls in addition to the input/output jacks.
Setting up an audio interface can be a bit daunting at first. Hopefully this page provides generic information that may clear up confusion common to most interfaces.
Contents
Installation
All interfaces are a bit different, and you should refer to the manufacturer's documentation for installation; however, there are a couple of quirky things I would like to emphasize.
- Some interfaces may be powered via a Firewire or USB cable as well as its own power adapter. Be careful - some are not meant to be powered by both simultaneously and can will be damaged if set up that way. When in doubt, try using the interface without its supplied power adapter first. On the other hand, some USB connections might not provide enough power, even if they should, such as if you connect to an unpowered USB hub that has numerous devices that use USB power. If things aren't working as they should, it's best to try to do some research or contact the manufacturer before experimenting and frying the interface.
- If your interface connects via a PCI or PCI-e card, the location of the slot on the motherboard may affect its performance. Generally, the slots furthest from the bottom have higher IRQ's than those towards the bottom. That means interrupts from the interface card can trump interrupts from cards below it and achieve better performance. Sometimes, there are motherboard BIOS options to adjust the priority the card can have.
- Not all manufacturers implement protocols the same way. My firewire interface recommended using a firewire controller that uses Texas Instruments chips. So I bought a PCI card with TI chips to provide the firewire ports to connect to the interface, rather than use the motherboard's firewire port.
- If installing a card into the motherboard and things don't work correctly at first, try powering down and reseating the card, or try using a different slot.
- Not all USB ports are alike. Sometimes the motherboard divides them between multiple controllers, with some functioning better than others. If you experience poor performance, try switching ports and testing.
Hardware/Physical Connections
The analog physical inputs for interfaces resemble the components of a mixing board. Most inputs have a gain/trim control and pre-amp, and microphone inputs typically feature phantom power switches. Instrument-level inputs often have a pad button in addition to the gain/trim control to attenuate the volume of the inbound signal.
Whereas a mixing board may be analog or digital, audio interfaces are designed to convert the analog signal into digital audio. Whereas analog clipping may be mildly annoying or in some cases musical, digital clipping is usually quite noisy and harsh. Properly setting pad and gain/trim settings to avoid digital clipping is essential to getting a usable signal in your DAW.
Cheaper interfaces don't always have great pre-amps, pad circuits, and A>D converters, preventing them from sounding good regardless of what settings you use. It's a good idea to not only look at general reviews of interfaces but reviews that specifically address your primary use cases before buying. Do not rely on features alone. I find it's better to sacrifice features in favor of quality signal transfer.
Many interfaces' inputs are designed to accept either microphone or instrument-level signals. They look similar to an XLR jack, but with a hole in the middle for 1/4" TS or TRS jacks. These will often feature pad, phantom power, and trim/gain controls. Other interfaces will keep XLR and TS/TRS jacks separate, with phantom power and pad controls only found on the XLR and TS/TRS inputs, respectively. These inputs are typically found on the front of the interface.
Line-In inputs are typically a pair of balanced 1/4" jacks and found on the rear of interfaces. Other formats would include the unbalanced red and white RCA jacks used on consumer devices, which is useful to connect a CD or mp3 player. They are designed to accept a stereo signal, but can be used to input 2 separate mono inputs.
SPDIF input/output is also found on the rear of the interface as a pair of jacks. These may be optical, coaxial, or both. Coaxial appears similar to RCA jacks but using an orange color rather than red or white. Although the connection is identical to RCA, RCA cables are typically a different resistance as cables designed to transport SPDIF digital audio - standard RCA cables may work, but may intermittently lose their sync...or they may not work at all. Optical cable is often referred to as TOSLINK to avoid confusion with coaxial cables and use a different jack. I don't find optical cable to be worth the extra expense for home recording, but it's generally not that expensive and often thinner than coaxial cable, creating less clutter.
For outputs, interfaces typically feature pairs of balanced 1/4" analog outputs, one of which is likely to be used for studio monitors. Others can be used to feed external gear, such as external effects or a guitar rig for reamping. There's also SPDIF out which is useful when you need to send your signal to other digital gear - this bypasses the set of D>A and A>D conversion that would happen if transmitting via analog cables.
Drivers
Most interfaces come with their own setup CD that includes the hardware drivers used for the OS or DAW software to communicate with the device. Before installing off the CD, you may want to look at the manufacturer's webpage to download the latest software/drivers - there's a good chance a later version was released.
For Windows, the preferred driver is usually ASIO. (ASIO is actually just a protocol - a driver simply implements ASIO. This means every ASIO-compliant driver is device-dependent, and you can't use the driver for one device on another.) Microsoft's default sound card driver is DirectSound, which is processed and buffered at multiple stages by the Windows OS before actually reaching the device. ASIO bypasses the Windows sound kernel (KMixer), avoiding both latency and unwanted processing by the OS, leading to both higher quality and greater availability of computer resources.
Using ASIO usually requires nothing more than installing the manufacturer's provided software. If you look in Device Manager, the driver may not explicitly say ASIO even if it is. There should be no need to change the preferred driver through Device Mananger. In your DAW, however, when selecting your audio interface, you may see your device listed multiple times with different driver names - DirectSound, WDM, MME, and ASIO. Given the choice, you should select ASIO.
ASIO is not an open standard, requiring a license for a DAW or hardware manufacturer to implement it. Thus, some do not natively support it. A popular alternative when an ASIO driver is not provided for your interface is ASIO4ALL, which is a free "driver" that uses advanced WDM techniques to achieve ASIO-like performance from devices that use a WDM driver. I find it's best to try to avoid the issue altogether by using ASIO compliant interfaces and DAW software. Getting ASIO4ALL to work correctly can be tricky or impossible.
Control Panel
Your interface should come with software to control it, often labeled "mixer" or "control panel". This often lets you do various things with inputs and outputs similar to real-world mixing board; however, not all interfaces feature these options - in those cases, the DAW software is routing directly to the physical outputs on the unit as well as handling all monitoring and leveling. It is also where you set the sample rate, clock source, input buffer, and SPDIF source.
Inputs/Mixer
The mixer or input tab of the control panel might not exist, depending on your specific interface. Some manufacturers rely on your DAW software to handle the routing listed here, which depending on your DAW, may or may not be available. It provides an additional layer of mixing/routing between your DAW's output and your interface's physical outputs, as well as allowing you to level and pan your physical inputs.
The controls typically resemble a mixing board. The page includes the physical inputs on your interface as well as software return inputs from your DAW which your DAW will see as outputs. You can do standard mixer operations for each of them, like leveling, panning, muting, and soloing.
Your DAW should automatically see all of your interface's physical inputs without having to change anything here, although you may have to add them inside your DAW software's setup. Different interfaces will provide your DAW software with different numbers of virtual outputs, and again, you may have to set that up inside your DAW.
Each input is likely to have a set of buttons that represent the available physical outputs. Routing a physical input directly to an output is called direct monitoring or hardware monitoring. The software tells the interface to route the signal directly from input to output. This allows you to hear your playing without any latency - the signal does not have to be digitized, routed into the computer, processed by the DAW and/or the operating system, routed back to the interface, and converted back to analog.
Routing the software return inputs to outputs is what will allow you to hear the output of your DAW software or other audio player software on your computer. Of course, you can often do more advanced things here, and it might be a little confusing at first. Let's look at a few examples.
- Guitar > Mic'ed Amp/Cab > Interface Mic Physical Input > DAW > Software Return Inputs 1/2 > Interface Mixer Settings > Interface Outputs 1/2 > Monitors/Headphones
- Guitar > Mic'ed Amp/Cab > Interface Mic Physical Input > Interface Mixer Settings > Interface Outputs 1/2 > Monitors/Headphones
- Guitar > Interface Instrument Physical Input > DAW > Software Return Inputs 3/4 > Interface Mixer Settings > Interface Output 3 > Mic'ed Amp/Cab > Interface Mic Physical Input > DAW > Software Return Inputs 1/2 > Interface Mixer Settings > Interface Outputs 1/2 > Monitors/Headphones
Notice how the "Interface Mixer Settings" appear in the above examples - this determines how the DAW outputs (seen as software return inputs by the interface) are routed to the interface's physical outputs. In our examples, we have the mixer set to route software returns 1/2 to physical outputs 1/2 and software return 3/4 to physical outputs 3/4 (but we only use output 3 to feed the mono guitar amp).
Example 1 is a typical guitar recording setup. You are not routing the physical input directly to any output, but picking it up in the DAW where it is recorded to a track and output to the master bus, which sends it to outputs 1/2. The Mixer sees that as software return inputs 1/2 and routes that to interface outputs 1/2, which are connected to your studio monitors.
Example 2 is how you would monitor your rig through your monitors without using DAW software.
Example 3 routes the guitar directly into the interface, so that it can be recorded as a DI track in the DAW. This would allow you to reamp the track later. It is then routed back to the interface where it is sent out of physical outputs 3/4. This connects to the amp/cab, which is mic'ed and routed into the interface, which is recorded as a separate DAW track and returned to the interface and output to the studio monitors (same as example 1). While this method will work to record both direct guitar and the mic'ed amp/cab simultaneously, the signal is getting routed around quite a bit before finally getting to the monitors (and even the amp/cab). Thus, it may have a bit of latency that makes it difficult or awkward to play in time during tracking. A better method to record both dry and wet guitars would be to use a DI box to split the signal, sending the signal from the DI box and mic'ed cab to different inputs on the interface.
When you are tracking, you may prefer to route your physical inputs to your monitor outputs - this will minimize latency, which may assist your performance. Also, you will need to do this to hear yourself through the monitors if you are not using DAW software at that moment. If you are mixing, reamping, or recording from a player or a natural sound source, you may prefer to disable direct routing in your interface, and let the DAW determine if you are monitoring the input or not. Be careful - if you route a physical input directly to an output and monitor it via the DAW, the signal from the DAW may have more latency, causing the mixed signals to have a comb filter. Even without latency, it would make the guitar sound louder than it should, possibly clipping the interface's output.
The software return inputs are what your DAW sees as outputs, so set them up accordingly. Generally, you only want to monitor the master output bus, which should be routed to outputs 1/2 in the DAW. In your interface mixer, you thus want to route software return input 1/2 to the physical outputs connected to your monitors, which are also usually 1/2. You may use Line Outs to run to other gear, or reamp via SPDIF. The best way to avoid confusion is to route each software return input to the same-name physical output. In some cases they are labeled differently, and you can order them by priority. For example, if you often use the physical "Line Out" outputs to run to an effects processor, you can assign them to the next open software return input, such as 3/4.
The input mixer may have additional level and pan controls. Sometimes these are linked to hardware controls on the device itself. These may not be able to prevent input clipping by lowering them - usually you need to use analog pad switches and gain knobs that attenuate the signal before hitting the A>D converters; however, some advanced devices will control analog circuitry through software. Generally, you will leave these at max volume and center pan, manipulating such things in your DAW.
There may additionally be typical mixer functions such as solo and mute buttons, which work the same way as they would on a mixing console, covered on the Mixing Boards/Consoles page.
Outputs
The control panel often includes an output tab or page similar to the input/mixer page, but pertaining only to the control of the physical outputs. There are basic mixer controls here - solo, mute, level, and balance/pan. There may also be a control to link the levels of multiple outputs, so they are all adjusted simultaneously. Often a headphones output may not be a routing option for the inputs, but the headphones output can monitor any of the other outputs, which is selectable on the outputs page. Again, I usually find these controls to be unnecessary and use the DAW's controls instead, except for things the DAW doesn't cover, such as which outputs the headphones monitor.
Clock Options/SPDIF Source
The interface usually has the option to select the SPDIF clock source as internal or external (master or slave). Many devices require being the clock source; and in this case, you must select external or slave as well as setting the correct sample rate to sync with the device.
Otherwise, you should use internal/master and set the sample rate at the rate that you want to record in. The DAW may be able to override this value, but it's best to set it to the same to keep everything consistent and minimize confusion and risk of error.
Lower sample rates means smaller file sizes for storing DAW tracks and less CPU power needed to apply plugins or handle numerous audio tracks.
For interfaces that have both coaxial and TOSLINK SPDIF input, you should be able to select which ones you are using for input and output.
Note: the sample rate selected does not affect the operation of the A>D converters. These always operate at the device's maximum sample rate, providing the highest quality A>D conversion. The signal is then digitally scaled down to the selected sample rate, without any loss of quality, other than the removal of frequencies above the Nyquist frequency.
Input Buffer/Latency
Communication between the interface and the rest of the computer is not instantaneous or reliably timely. For a slower computer or one bogged down with other tasks, it may not be timely at all. This results in crackles and pops in the audio signal, as the stream is constantly being interrupted and dropped. To prevent this, the interface can store the audio stream in an input buffer, a temporary memory location, where it can be reliably transported to the rest of the computer when the computer is ready to receive it. In turn, this means that it takes longer for the audio to get to where it is supposed to go, resulting in latency between the input into the interface and the DAW's ability to record, process, or monitor it.
Interfaces often allow you to set the buffer size in terms of samples or miliseconds. You should set it as small as possible so long as the audio never drops out or pops.
While the DAW is smart enough to account for this latency, it may make it difficult for the musician to record if using software monitoring. This latency can be avoided by using direct monitoring (routing the interface's physical input directly to a physical output). It can also be minimized by using proper low-latency drivers (typically ASIO) and setting up your OS and DAW software to efficiently work with audio. Or you can use a more powerful computer.
Besides driver and OS settings, certain interfaces may be able to transport its data more quickly to the computer depending on the bus with which it uses to communicate. USB 2.0 or 2.1 can sometimes run into issues, although theoretically fast enough. Firewire is typically faster; however, this depends on the Firewire controller in the computer - some interface manufacturers recommend certain controller chips over others for best reliability and speed. Interfaces that use a PCI or PCI-e card may benefit from being seated in higher slots on the motherboard to obtain a higher priority for its interrupt requests. USB 3.0 is relatively new but should be more than fast enough to achieve imperceptibly low latency.
Connecting to DAW Software
Once you have your drivers correctly installed and your OS has recognized your interface, the next step is to open your DAW and select your interface. Every DAW software does this a bit differently, but most of the time, you should find the settings on the Settings or Preferences dialog under an Interface, Connections, or Hardware tab/page. You should be able to select the interface. Sometimes it does not appear as expected, either listed under a generic name like "ASIO Device" or listed multiple times with different drivers. You typically want to select the option that uses "ASIO", which is the lowest latency driver, and typically the only one that talks to your interface. DirectSound, WDM, or MME is not what you want - these are generic Windows drivers that do not allow DAW software direct access to the interface and buffer the audio streams through levels of the OS as well as process them before sending them on.
After you have selected your interface, you will want to setup your inputs and outputs. Often the DAW software will do this automatically, but it may omit all of the possible choices. Check the I/O page(s). If all your inputs or outputs aren't listed, you may have to manually add a bus for each (or each pair) of inputs and outputs - you will get the option to select the physical inputs that correspond to the bus as well as being able to label it to match the physical I/O it pertains to.