OTx2 Old Timer needs assistance on audio/midi usb interface

Lots of interfaces from the $150 on up will have combination inputs for however many preamps they have, which accept either a 1/4" input or an XLR input.
 
My Presonus 1818VSL has phantom power available for all 8 inputs, with the first 2 inputs being for either mic/instrument and the other 6 inputs being for either mic/line.
 
I always use one of the first 2 inputs for plugging in guitars - seems to work well.
 
A large part of your purchase cost for an audio interface will be based on the number of inputs and pre-amps it has, so figuring out what you need ahead of time will either save you money or will frustrate you, if you don't get it right.  Some vendors use cheap pre-amps and have a lot of inputs, and some have few inputs but have really good pre-amps.
 
I would do some soul-searching on determining the number of inputs needed, calculate the budget, and then do some homework on the various vendors that market interfaces with the number of inputs you need, balancing it all against how much money you have to spend on them.
 
Good luck, and I hope you find something that in the balance of it all fits your needs.
 
Bob Bone
 

Guitar inputs are called Hi Z in that they have a different impedance than line level inputs. They are for direct connection of a guitar to the interface without needing a pre amp and/or amp.
 
Unless there is a switch for changing the impedance I would not use them for normal line inputs if you can avoid it.
 
Most audio interfaces today come with mic and line level inputs. Some are switchable others are independent. Hi Z is useful if you plan on using a guitar directly with it.  
 
 

The spec sheets are a little confusing, since they typically do not (at least in the short "features" version) show what kind of current/impedence is supported. So it is common to see that a unit has XLR or TRS connections, but the seller assumes that you will assume these connectors are to line level connections, so the fact that they are "line level" is omitted. XLR connectors or combination connectors accepting XLR are typically (but not always) connected to built in microphone pre-amps. If the spec sheet fails to mention pre-amps it is safe to assume that none are present. HIgh Z matches the output of an unamplified electric guitar, and it is now pretty common to find connectors that will accept an electric guitar (TRS with internal High Z), an unamplified microphone (XLR with built in preamps), a and a TRS keyboard audio out (line level) in the same connector. RCA connectors are not common in computer audio interfaces, since they are more commonly used to connect electronic components than instruments. Digging into the manual or full spec sheet will usually clarify the issue of what type of electrical connection the socket supports.