Applies to all Focusrite interfaces and preamps.

Focusrite interfaces and preamps feature several types of inputs, allowing you to work with a variety of audio sources, including the following:

• Mic — Microphone level
• Line — Line level
• Inst — Instrument level

These three signal levels may have their own dedicated XLR or 6.35mm (¼″) inputs. However, many of our products include combo connectors that accept both three-pin XLR and 6.35mm (¼″) jack. The XLR section of the connector is dedicated to microphones, while the 6.35mm (¼″) jack in the centre accepts both line level and, in some cases, instrument level. There is a hardware or software switch to change between the two where instrument input is available.

XLR input

6.35mm (¼″) input

Combo input (both)

Microphone level

Mic level is a very low signal level that requires amplification by a preamp. It is produced by microphones, but also by DI boxes and some other devices, all of which typically connect via XLR. All Focusrite products use XLR for mic-level connections; you won't find a mic setting on products with combo inputs because the XLR portion is dedicated to mic-level.

Line level

Line level is a much higher signal level. Most audio equipment outputs line-level, though the exact level can vary between consumer and professional equipment. Synthesisers, drums machines, keyboards, outboard effects, and many mixers output line level. Even headphone outputs on phones, tablets, and laptops — while not strictly line-level — can be connected to line inputs. 

Equipment designed to power passive speakers, like power amps, certain mixers, and guitar amp speaker outputs should not be connected to line inputs, as it can severely damage them. For more information, see ‘speaker level’ below.

A variety of connectors can be used for line-level signals, but most current Focusrite products feature 6.35mm (¼″) TRS line inputs — check your user guide or any input labels if you're unsure. TRS refers to the number of conductors in the cable and their positions on the connector:  Tip, Ring, and Sleeve. The advantage of TRS is that it can carry a balanced mono signal, which helps prevent noise. You can still connect TS cables to your TRS inputs; the signal will just be unbalanced.

6.35mm (¼″) TRS

6.35mm (¼″) TS

It's important to note that, while TRS cables can be used to carry unbalanced stereo signals, all TRS inputs on Focusrite products are balanced mono. You will need to use two of these inputs for a stereo signal.

If you would like more information about the differences between TS, TRS, balanced, and unbalanced connections, see these two articles: What are TS, TRS, and TRRS connectors? and Differences between balanced and unbalanced audio.

Instrument level

Instrument level is the most variable signal level and comes from a wide-variety of guitar and instrument pickups, almost always using a 6.35mm (¼″) TS jack. Like mic level, it requires amplification by a preamp. Additionally, instrument-level signals are generally always unbalanced.

6.35mm (¼″) TS

To connect an instrument with a pickup directly to your audio interface or preamp, first check that you're using a 6.35mm (¼″) input that accepts instrument level. This should be indicated on the input label, or by the presence of an instrument button, and you can also check the user guide. If the input accepts both line and instrument level, enable the instrument level switch on the hardware or in the control software.

What are the differences between these input types?

When you select a mic, line, or instrument-level input, two main characteristics change to accommodate the different signal levels:

• Impedance — Impedance is a measure of the opposition to electrical current passing through a circuit, such as an audio signal passing through a preamp. To preserve tone and volume, the input impedance must be appropriately matched to the source impedance. For example, when you set an input to instrument level, it switches to the impedance of a guitar amp, ensuring your guitar comes through clearly.
• Maximum input level — Analogue audio consists of electrical signals that can vary greatly depending on the source. Stronger signals result in higher input levels. For instance, a synth's output will be far higher than a mic. By adjusting the maximum input level, you can match the appropriate signal level to each source, ensuring the signal is neither too weak nor overloading the input.

Typical impedances and maximum input levels for Focusrite products:

*Maximum input level measured at minimum gain.

For exact specs, refer to your user guide and the product pages, as impedance and maximum input levels may differ from those listed above.

What about outputs?

Other than headphone outputs, the analogue audio outputs on all current Focusrite products are line level, generally balanced using 6.35mm TRS jacks, although some may use XLR, and there are some older products that use unbalanced RCA. See 'headphone level' below for more information regarding the headphone outputs on Focusrite products.

What other types of audio signal are there?

Headphone level refers to the type of signal produced by headphone outputs, including those on our products. While it is to a large extent similar to line level, the impedance requirements of headphones are different, which can result in low volume or poor audio quality when connecting headphones to line outputs. Also, all headphone outputs on Focusrite products are 6.35mm TRS, but they are unbalanced stereo, rather than balanced mono.

To check what impedance of headphones your Focusrite interface can drive, check this article: What impedance headphones should I use with my interface?

Speaker level is a much higher voltage signal used to drive passive speakers, like you might connect to guitar amplifiers or other power amps. Due to the high voltage, low impedance (typically 4 – 16Ω) and resulting high electrical current, a speaker level signal can damage inputs designed for lower signal levels, like mic, line, and instrument. Focusrite products do not output speaker level.

Inserts consist of a line-level output and input intended for sending audio directly from the preamp to outboard effects and processors, and returning it to the same channel on the preamp. The input and output may be provided by separate ports, or combined into a single unbalanced TRS that can be split into the send and return signals with a TRS Y-splitter cable, as they are on the Clarett OctoPre — How do I use the insert points on Clarett OctoPre?

There are also a variety of digital signal formats, including ADAT and S/PDIF. These carry digital audio via electrical or optical signals, rather than analogue audio.

For more information about these digital signal formats and how to use them with your audio interface, have a look at these links for ADAT and S/PDIF.