The recording interface you get will determine how many channels you can record simultaneously, and will provide all your inputs and outputs.
The main purpose of the interface is to provide a hub for all your inputs and outputs, and provide routing of all the channels in and out of the computer. Some interfaces provide lots of inputs, and some provide lots of outputs. Some have options for expansion, and some have built in DSP (digital signal processing)
This lesson assumes you already know about the different connectivity options on an interface. If not, check out lesson 1.6 where that is all explained.
Choosing the right interface will take time and research to find the right balance between cost, quality, and features.
Interfaces have different methods of plugging into the computer. USB is the most common, and I think I would even recommend it. In the past, USB was sluggish and not capable of high channel counts, but the technology has improved a lot, and is now capable of 64 channels in and out with no problems. Some interfaces use thunderbolt or Ethernet for connectivity, as they are capable of even higher channel counts.
One of the first things to decide, is how many inputs and outputs you will need. If you are recording just 1 channel, such as a podcast, you don’t even need an interface, a USB mic will work just fine.
If you sing and play guitar, and just want to record yourself, a 2 channel interface that has 2 microphone preamps will be just fine. This same interface will also likely have 2 outputs, for connecting monitor speakers, and a headphone output.
As you grow and want to record larger projects, you’ll need more inputs. These can be in the form of xlr microphone inputs, 1/4” balanced line inputs, or digital expansion connectivity.
If you want to use an external preamp, which are often better quality than the preamps built into the interface, you’ll want to plug the preamps output into a 1/4” balanced line input on the interface. The idea is to not use the interfaces preamp. Be aware, Some lower quality interfaces will use a combo jack to offer either 1/4” or xlr input on the same channel, and the 1/4 input does not bypass the preamp. In these cases, there is no advantage to using an external preamp.
Digital expansion connectivity can give you the option of purchasing separate ad/da converters to increase your number of inputs and outputs. This will usually be in the form of an optical cable, called ADAT, or ordinary xlr cables or 25pin d sub cables, called AES/EBU. For more information on these connection standards, check out lesson 1.6.
And how many outputs do you need? The minimum is 4, so that you have 2 for your monitor speakers, and 2 for a headphone output. Headphone outputs are 2 channel because there’s separate signals going to the left and right channels.
There are a few reasons you might want more outputs.
- if you have a band practicing, or recording, more outputs can be used to send each band member their own headphone mix. Many interfaces will have a digital mixer which you can control on the computer, and control the levels of headphone mixes.
- if you like to use hardware gear, such as a rack mount reverb unit, or an analog compressor. You can route a track out your extra output channels, and into your piece of gear, and then to an input channel where it gets recorded back in.
- if you want to use analog mixing, also called “out of the box” mixing. Check out lesson 5.2 for more information on this.
A lot of interfaces have built in DSP. That stands for Digital Signal Processing. It gives the ability to add effects, such as reverb, compression and eq, directly within the interfaces mixer. When you route the signal to the recording software, you have the option of recording it with the effect already applied. You will also have the option to use the effects for monitor mixes, or a live mix into a PA system. The reason built in dsp is useful is because for real-time playback, you can add these effects. If you were to try and use the effects available in your recording program for real time, live application, it would require complicated routing in and out of the recording program, and there would be noticeable latency on the effect. It’s not really feasible. So, if you will be using the interface for live mixing or live monitoring, built in dsp can be very useful.
Many interfaces provide midi in and out. This feature is more of a thing of the past, as midi is not controlled by the audio drivers, so it is easily implemented through a separate USB connection. If your interface has midi in and out, then that’s nice, but if not, then don’t worry about it because you can easily add midi in and out to your computer with a midi to USB cable.
Regarding sound quality of interfaces, you generally get what you pay for, with some brands being a bit better than others. For instance, there are many interfaces available that are 2 in and 4 out, with no additional features. They usually cost between $100 and $200. But then the Apogee Duet costs over $600! The reason for this is that the Apogee Duet has better quality preamps, better quality amplifiers on its output channels, and headphones, and uses better quality ad/da conversion. All these things combined make for overall better sound quality.