Mic vs Line vs Instrument Inputs

[TheEclectic]

I am looking at upgrading my USB 1.1 audio interface to one with USB 2.0 and I am trying to get a grip on this concept. I have searched the internet and still I have no real understanding.

It looks like most audio interfaces are setup to have a one or two mics, one or two instrument-ins and all of the rest are line-ins. Doing some experimenting with my gear, it looks like I need to run my instruments and my Roland VG gear thru a mic preamp in order to get the line-in signal as strong as the instrument-in signal.

Is this what people normally do? What about "DI" boxes - do they do the same thing as a mic preamp or are they somehow different?

Now I am starting to understand why some of my recordings sounded a bit weird - as was running my instrument level gear thru the line-in and I was altering my tone for the worse.

[jamsire]

I am looking at upgrading my USB 1.1 audio interface to one with USB 2.0 and I am trying to get a grip on this concept. I have searched the internet and still I have no real understanding.

It looks like most audio interfaces are setup to have a one or two mics, one or two instrument-ins and all of the rest are line-ins. Doing some experimenting with my gear, it looks like I need to run my instruments and my Roland VG gear thru a mic preamp in order to get the line-in signal as strong as the instrument-in signal.

Is this what people normally do? What about "DI" boxes - do they do the same thing as a mic preamp or are they somehow different?

Now I am starting to understand why some of my recordings sounded a bit weird - as was running my instrument level gear thru the line-in and I was altering my tone for the worse.

Alesis and M-Audio have these products. Also, the Tech 21 XDI box preserves the line signal.

[lactose]

I own the M-Audio preamp and use it in front of my Delta 44. For me it was pretty obvious right away that I needed the preamp. My guitar wouldn't light up the LEDs on the interface at all.

[Jersey Ray]

I'm far from an expert on the topic... but

yes you need to use some kind of pre-amp to boost the signal from guitar level up to line level. A direct box with an active pre-amp migh also fulfill this purpose.

I have noticed more and more, though, that some of these computer interfaces have dedicated guitar inputs. These will accept low level guitar signals. The Line-6 products have been this way for years, with software to model all the amps and such.

good luck!

[lord_avon]

hi,

ok, there are two things to bare in mind abotu the various input types.

1. mic inputs, normally very low impedance (600ohms) and low signal level
2. Line inputs, mid range impedance (~10Kohms) and nice big signal level (1V peek to peek).
3. Guitar inputs, very high impedance (100Kohms up) and another low signal level.

The important thing when connecting these things together is match BOTH the impedance and signal level.

Most tapping instruments fall into the "3" catagory.

Those with active pickups (bartolini's, etc) have a slight twist, in that they're somewhere between number 2 and 3, having an impedance close to the line level, but a signal that's quieter than line level, but MUCH louder than a standard passive guitar pickup.

Plugging a line level output FX send on a desk into a standard guitar pedal will distort it to hell usually. Plugging a guitar or mic into a line input usually means you hear next to nothing without the gain cranked up full and then you get a lot of "hiss".

What a DI box does is two fold, it matches BOTH the signal level and impedance of the mic to itself, and then "amplifies" it and outputs it with an impedance and signal level to match the output (normally line, often balanced line, i.e. XLR).

You can get guitar preamps, and audio interfaces with guitar inputs, but most only have ONE input, kind of useless for most tapping instruments.
So you'll need two DI boxes, or two Preamps.

I'm building myself a little battery operated, stereo preamp ready for when my megatar arrives. The idea being I can plug my Megatar into it, then from that into my Micro-BR's stereo line in, and jam away whilst on holiday without taking preamps, desks, power amps, etc.

I could make it so it could also be run from say a 9V DC wall wart (like a pedal) and hooked to a stereo line input interface if people wish.

I'll happily share the schematic when it's done and tested, if anyone is interested.

Paul