If you use a computer for music recording and production, you will need a good quality audio interface. Beyond the obvious question of available budget, the particular requirements of the user has to be considered while narrowing down the options to choose an audio interface suitable for you. Here we discuss about making the buying decision easier.

The basic use of an audio interface is that it lets you record external sounds such as vocals and instruments into your computer, converting them from analogue to the required digital format, and from digital to analogue when the signal passes from the computer to amp/loudspeakers. The conversion between analogue and digital is written in short as A/D-D/A

To record midi within a computer, you don't need an audio interface, though having a good sound card can help the computer to speaker connection and the final output sound.

There's now a very wide range of audio interfaces available at a price range from within Rs.5500 (USD 100) to what is affordable by only a few in the world. The good thing is that affordable audio interfaces like the Focusrite Scarlett or the Focusrite Saffire are of high quality with very good components, and are enough for us to make pro quality recordings. Since i personally know that they are used for pro sound recording and production, I can assure you that at least a part of the professional music you listen to and like these days are made using these small and handy audio interfaces.

Along with the budget, consider what the interface is going to be used for.  For example:

  • The interface used to record computer based music is different from what will be needed to record a live band.
  • Lesser the number of inputs and outputs needed, better the quality of interface available for a given budget. Naturally 2 input by 2 output audio interface will cost lesser than an interface with similar quality that has 8 inputs by 8 outputs.

What do you want to record?

Decide the number of simultaneous inputs needed for the audio interface, based on the recording needs. Let us have a look at the different types of inputs used while recording.

The different kinds of analogue inputs

Line level 

Line level is the simplest input, used for connecting electronic equipments like mixing desks, CD/DVD players, synthesizers and pre-amplifiers. Output of microphones is at a much lower level and that is why line level inputs are not enough to connect and record microphones.

Preamps – microphone inputs

Since a microphone output level is much below line level, we use a preamp to raise the signal level to line level. This is done before the signal enters the computer through the analogue to digital conversion.

Preamps with phantom power

Capacitor mics require a preamp that can supply 'phantom power'. A phantom power switch is provided for the preamp to be used when connecting condenser mics.

The Focusrite Scarlett 2i2 is a 2 in / 2 out USB recording interface featuring two award-winning Focusrite preamps. The front panel Neutrik combination input can be used to connect line and instrument level signals as well as microphones. And it’s solid enough to take on the road when you travel

Instrument inputs

The output levels from electric guitar or bass, peizo pickups of acoustic guitars etc fall in between that of a mic and a line in.

The signal from these sources are louder than than that of mics. We need to keep the input level considerably low to make a recording by connecting an instrument kind of input to a mic input.

Another difference in the case of instrument inputs is that magnetic pickups need a higher impedance to prevent high frequency loss. Passive pickups of guitars or similar instruments need impedence in the range of around 100k(omega) to 1M(omega).

The use of DI box If an audio interface suits you except for the lack of an instrument input, you can buy a DI (Direct Injection) box. A DI box will change the signal properties and let you plug your instrument to the mic input.

If you want to record with one or more mics and are starting from scratch, the most cost-effective option is to choose an interface with suitable mic preamps built-in. Those who already have an analogue mixing desk with input channels offering mic preamps and direct outs can patch these into the line-level inputs of an audio interface, while those with larger budgets can investigate more sophisticated stand-alone preamps that offer particularly clean or desirably 'coloured' audio.

Deciding the inputs for your audio interface

The Focusrite Saffire 6 USB is a two-in/four-out USB audio interface. It uses the award-winning Focusrite mic preamps

Computer musician

If you work with pre-recorded samples, loops and software synths, and do not record any signals at all (no recording vocals, guitar etc), the most basic stereo line-level input will be enough. Even if you don't use the two inputs for recording, they may come in handy for an occasional recording or just to transfer some analogue based music into your computer.

M-Audio Audiophile 192 Hi-def Aud Card which sells at around USD80 at the time of writing, is an example of a basic budget interface with two analogue inputs and outputs. Though, personally i recommend to put in a few more dollars and get an affordable Focusrite audio interface because it can make a difference to the sound and have additional features for a bit more of the money spent.

Solo musician

If you need just one mic input for vocals and one or two (stereo recording) instrument/line-level input for guitar/bass/keyboard, get an interface with two 'versatile' inputs that can accept mic, instrument and line signals. You can use these interfaces for multi track work too, by overdubbing, which should be fine unless there are too many analogue sources to record at the same time. Focusrite Scarlett or the Focusrite Saffire are among the best in this category.

Recording other musicians

You need more inputs when recording if you work involves recording more than one musician at the same time. 2 inputs and 8 inputs models are most common while 4 input is rare. If you want to record a band simultaneously, going for a minimum of 8 inputs maybe needed.

8 in 8 out

Interfaces in the 8-in/8-out line-level analogue format are available, though we may choose to have models with eight mic preamps instead of line ins built into the interface.

8 mic preamps

If you would like models with eight mic preamps built in to the interface, try Focusrite Saffire Pro 10I/O, the PreSonus FIREPOD, M-Audio ProFire 2626 ($400), and MOTU 8pre and MOTU 896mk3 Hybrid.

Other combination of input outputs are also available, like the MOTU UltraLite-MK3, which offers two mic/line/instrument inputs, six line-level inputs and 10 analogue outputs.

Read about them, the details, check the input and output needs you will have, and be convinced that they are suited for your needs, before you decide on one.

Adding more inputs

Live backing vocals, stereo inputs from keyboard, guitar processors, large number of live instruments etc may require an expansion in the number of inputs available for recording simultaneously.

There are two main ways to further increase the number of analogue inputs: 

Expand using ADAT

The easiest way to get more input and outputs is to buy an 8-channel combined preamp/converter box such as as Behringer's ADA8000 or one of the Focusrite OctoPre series, and plug its output into the ADAT input port found on many audio interfaces. Each ADAT port supports up to eight extra channels at standard sample rates.

Super interface

We can combine 2 pieces of the same audio interface with 8 inputs to work together, giving a total of 16 inputs. Most models allow us to use 4 pieces together, giving a total of most support up to four devices, giving us 32 inputs and outputs.

For this to work on a computer:

  1. The device manufacturer should provide multi device drivers
  2. There should be a way to lock the digital clocks so that all the inputs and outputs from the different devices work in perfect sync.

RME Fireface 800 is a popular equipment in this category, which includes two pairs of ADAT ports for further expansion, most often praised for the quality of the sound and ease of use. At their website, the manufacturer states that 'RMEs Fireface 800 is seen as reference by users and editors, when talking about FireWire audio and mobile recording.'.

Even if you need only one 8-input interface currently, buying one with multi-device drivers will make it much easier, if you have any need to upgrade later.

Interfaces with more than 8 inputs and outputs

MOTU 24 I/O has 24 analogue line-level inputs and outputs in its compact, 1U rackmount case, while a combination of Lynx's Aurora 16 and AES16 card will give you 16 ins and outs.

Digital inputs and outputs

Digital I/O allows us to connect compatible studio gear without additional analogue-to-digital conversion stages. Using the digital connection, we avoid using analogue equipments to pass the audio, thereby avoiding possible signal degradation.

S/PDIF (Sony Philips Digital InterFace) and ADAT (Alesis Digital Audio Tape) are two popular digital connectivity formats. When starting, you won't have to worry much about any of this. Later when needed you can find out what specialist digital connectivity is best suited for you.

The number of outputs

Deciding on the most useful number of outputs for your perfect audio interface is a partly academic exercise, since products mostly offer an equal number of inputs and outputs (notable exceptions include M-Audio's 4-in/10-out Firewire 410 and Echo's 2-in/8-virtual out Mia). This may seem bizarre to all those musicians who want to record a band and listen back in stereo and are therefore looking for an 8-in/2-out interface, so let's see what you can do with all the other outputs on the far more common 8-in/8-out models.

MOTU's 24 I/O Core System has 24 analog inputs and outputs at 24-bit/96kHz in a single rack space package, allowing you to connect and record from 24 simultaneous analog sources along with lot of output options.

Extra monitors or speakers

The main stereo outputs can be connected to the main monitors. Two of the remaining output channels can be connected to computer speakers or commercial speakers to know how the mix sounds in them.

External Effects

Outboard effects like analogue EQ, compression, tape/tube enhancement, reverb etc can be patched in using the extra output and input channels. One interface output is allocated for each mono send and one input for each mono return. Then using the sequencer, by choosing the appropriate output, send the signal to the external effect, connect the effected signal back in to the audio interface, take it back into the mix using the sequencer. Sequencers Cubase/Nuendo have in-built functions that compensate for the delay from the external effected signal.

5.1 surround

5.1 surround setup requires six outputs: left, right, centre, left surround, right surround and Low Frequency Effects channel. Audio interfaces with six outputs are therefore useful for a surround setup.

Some audio interfaces have in-built filtering and distribution features needed to direct the surround mix to the respective speakers.

M-Audio FireWire 410 4-In / 10-Out is an interface with lot more outputs than inputs.

To mix on external analogue gear

You could use the spare inputs and outputs to connect to an analogue mixer and mix the computer based tracks outside the computer; also known as 'out of the box' mixing. You can allocate each audio track or group tracks or stem submixes to separate hardware outputs of the audio interface, connect it to each track of the external mixer, mix it, then route it back to the computer as a stereo through two inputs.

Do this if you have good analogue gear and if you feel this kind of external mixing will add something good, instead of doing the whole process within the computer.


Many modern keyboard controllers and MIDI controllers provide a direct USB connection to computers, so that you may not need any MIDI ports at all. Edirol PCR-300 Midi Keyboard Controller is an example.

If you have more MIDI devices to connect, or if your keyboard does not offer any other option to connect to the computer, you will need a midi interface.

Many audio interfaces have a pair of MIDI in an out built in, so that you can use it for your midi controller or keyboard without having to buy a separate interface. This is better because it avoids any possible conflicts when you connect your audio interface and another midi interface simultaneously to the system.

Headphone Options

Using a laptop, a bus-powered audio interface and heaphones, you could run your whole recording or production system on battery.

Dedicated headphone-level outputs on the interface front panel lets you monitor while recording.  If you don't have loud speakers or if for some reason you prefer to use the headphones, the dedicate out will come handy while playback.

Two or more dedicated headphone outs are available in some audio interfaces. Even if headphone outs are not present, we can use the line outs to connect the headphones. We may need to raise the line level signal to make it loud enough in the headphones. Audio interfaces usually have analogue controls for headphone outputs. The main out usually don't have an analog control, which is a problem if you wanted to change the main volume fast, for example in the event of an unexpected loud noise. Focusrite products include this good feature and have analog controls for the main output, along with headphone level controls.

To be continued in the next post which will cover the remaining factors and conclude.