Audio Interface - How Many Inputs do I need?

Question

I'm new to audio interfaces and planning to buy either Focusrite 2i4 or 6i6. I have two keyboards and I want to connect those two to each other and then one to the audio interface.And also connect one keboard through midi to audio interface.

My questions are

• How many audio inputs do I need on the audio interface?
• I plan to buy
  • 2 mono to stereo line in cables to connect each keyboards' left and right channel to the stereo line in on audio interface.And
  • 1 one standard midi out cable for connecting the keyboard to the audio interface.
  • 1 usb midi cable for connecting one keyboard to the other.

Does this sound right?

• Also can I connect keyboard to XLR input the one that is used for mic?

Thank you.

Answer 1

Audio

First, be aware that each input jack on the interfaces you are considering (and the vast majority of audio interfaces) is mono, not stereo. So you will need 4 input jacks just to plug in your two keyboards. Admittedly, it's not entirely helpful that in their marketing language companies will say "stereo line input" when what they really have is two mono line inputs that you can gang as a stereo pair, but that's the way it is.

The good news is that you can plug your keyboards into the XLR jacks. Any time you see an XLR jack referred to as a "combo" jack, as it is on these interfaces, that will normally indicate that you can plug a standard 1/4" jack into the center of it and use it as a line jack.

So, for your audio setup, the 2i4 is not going to have enough inputs, but the 6i6 should be enough.

MIDI

Your MIDI plan sounds a bit odd. It sounds like you want to be able to daisy chain both keyboards to the MIDI ports on the audio interface. That is certainly doable, but the specifics of your plan probably won't work.

In particular, I doubt you will be able to chain one keyboard to the other using USB. If your keyboards actually support this, I want to know what they are! More likely, you will need to do your MIDI setup entirely with standard MIDI cables.

You will need 3 MIDI cables just to achieve a setup where one of your keyboards can both send and receive data with the computer (IN - OUT and OUT - IN between KB1 and the audio interface), and the other can receive data from the computer and/or the first keyboard (MIDI Thru on KB1 to MIDI IN on KB2).

The limitation in that setup is imposed by the MIDI Thru port, which is a one-way street. It's designed to send MIDI data from a controller to a sound module, not to support full two-way duplex communication where data is both coming and going. So you can have one keyboard as a controller, but not both.

To be able to use both as controllers, you will need an audio interface with 2 sets of MIDI In/Out ports, or a separate MIDI interface to support one or both of the keyboards. If you update your question with details of the keyboards you have and the objectives you want to achieve with your MIDI setup, I'll adjust my answer accordingly.

Answer 2

I think you need to provide more info before someone can really answer this completely. What kind of keyboards do you have, and, especially, what kind of output/inputs do they have? But I don't believe your description of what you want to do is possible on either of those interfaces. The 2i4 only has 2 mono inputs (these are both XLR and line-in, so you can use them for a mono 1/4-inch input, but then those inputs can't be used as XLR). So if you want both the L and R from your keyboards, you can only plug one into the 2i4 (L in one combi input, R in the other) before you've used up all the inputs. On the 6i6, you could use the 2 combi inputs for one keyboard's L and R and the rear line inputs for the other keyboard's L and R. You would still have 2 inputs left (but they're S/PDIF, which only works with some kinds of things), so technically that's more than you need.

Your plan to plug one keyboard's MIDI Out into the other keyboard should work via MIDI Thru, but I can't say whether USB will work without knowing the specific keyboards you have (I still might not know, since that isn't my area). Either interface should work with standard MIDI DIN cables. It's always potentially problematic to use MIDI and audio from keyboards simultaneously, because you can end up with echo due to your local playing also being sent via MIDI and then back out to the keyboard again. This depends on what you're planning on doing with the MIDI data being sent in.

So anyway, if you need stereo out of both keyboards, then you'll need at least 4 line inputs, so the 2i4 would only cover one and the 6i6 is technically more than you need. If money isn't a severe concern, then more is generally better, although I don't think there's a much use for S/PDIF inputs like the 6i6 has two of.

Answer 3

2 x keyboards = 4 line outputs->interface inputs (assuming stereo synths). On a 4-in interface all of your inputs will be constantly used up, so ideally you need a 6 or 8+ input one.

re MIDI - the synths are supposed to make sound, so they also need midi input, not just output. K1 I/O is 2 x MIDI cables, for K2 I/O you're either stuck with midi "thru" on K1 (if you have it, and then think of playing K2 sounds using K1 keys), or you can look for a 2 x MIDI i/o interface (a reason I keep my Midisport 2x2). It's worth checking if you can daisy chain your devices and avoid potentially messy MIDI data or latency.

As pointed in the thread, unless it's a universal input (hole in the middle) do not connect keyboard to microphone XLR input.

so:

• 6+ input audio interface
• 4 x single channel leads (TS/TRS)
• 3 or 4 x MIDI cables

The 6i6 has 4 analog inputs (2 universal instrument/mic, 2 x ¼” TRS). The rest is marketing talk - the S/PDIF requires a converter from analog but that chain is not necessarily in perfect sync with the rest, and also the converters may introduce a delay so if you're hoping to use it at full i/o, prepare to be surprised. It really is beyond me why Focusrite count a single MIDI input jack as 16 inputs. (6i6 = really 4 in 4 out 1 midi i/o 1 digital i/o).