I don't think you gave enough information. What keyboard? What interface? When you say 'access the sounds of the keyboard', are you trying to access the keyboard's sounds in GarageBand?

You must start thinking about ROUTING... it is very important. So far, your keyboard is routed into your audio interface, and then into your computer/GarageBand, right? This allows signals to be sent through your interface to GarageBand... and it allows the sounds within GB to be played. But how do the actual sounds within your keyboard get routed into your computer? Only through an AUDIO connection. You must come out of an audio OUTPUT(s) of your keyboard and into an INPUT (or inputs, if in stereo) of your interface. Have you done this? If not, you will not get the audio from your keyboard into GarageBand. MIDI is for sending signals from your keyboard through your interface into 'virtual' or 'soft' instrument. But internal keyboard sounds? Must be done with an AUDIO connection -- no amount of 'MIDI' will replace this. Hope this helps.

There are (at least) two types of outputs.. there are MIDI outputs, and there are AUDIO outputs. You must learn the difference between the two (see my earlier message).

Ok, so as far as I can tell from the docs that keyboard - sends MIDI out its USB connection to your computer [which it sounds like you already have working], - and sends audio [its own internal sounds] out the L/R 1/4" [audio] Outputs on the back - To play/record one of GarageBand's own instruments, make a Software Instrument track and select the Instrument you want in the Library [on the left, shortcut Y] -- MIDI data from the keyboard will trigger the notes from the internal Software Instrument and be recorded in that track, and the sounds during playback will still come from the internal instruments themselves - To play/record one of the keyboard's instruments, plug the keyboard's [audio] L&R Outputs into two line-level [1/4"] inputs on your audio interface [say, the smaller jacks in the middle of the larger XLR connections, like for Inputs 3&4 on your interface]. Make an Audio track in GB, and select the interface inputs you've plugged the keyboard into [for example, inputs 3&4] as the input[s] for that track [in the Smart Control panel at the bottom, shortcut B] -- an audio waveform will be recorded in that track, just as when you record a live [acoustic] instrument with a microphone As LoFo also pointed out, the key to understanding this is to understand the difference between audio signals and MIDI signals -- hopefully the previously-recommended course will help explain that..

Ok, this is getting confusing -- first you said you had access to the MIDI sounds (the Software Instruments] in GarageBand but not the audio instruments from the keyboard, but then you seem to be saying the opposite -- you did get the sounds from the keyboard on a Audio track.. Please clarify.. Earlier you'd said you were going to make the MIDI connection via USB, but apparently you've used the old-fashioned MIDI connectors on the keyboard and the interface instead. That's fine, there's no audible difference between MIDI-triggered Software Instruments whether you connect them via USB or the older MIDI jacks -- that's because there's no sound in MIDI [again, it is key to understand the difference between audio and MIDI to avoid confusion].

Ok, to answer your question on the interface input hookup.. You said I don't know how to select the interface inputs for the audio track - Select the audio track - Hit the shortcut B to open the Smart Controls panel at the bottom [if it's not already visible] - At the bottom, under Recording Settings > Input select the interface inputs you plugged the keyboard's L&R audio Outputs into - Arm the Audio track [explained in a previous post] -- you should be able to hear the keyboard instrument and see the level in the audio track's meter, and when you record you'll see the waveform for the instrument And to clarify what you do or don't already have working.. You said I have access now to the sounds of the keyboard Does that mean you can play, hear, & record the keyboard's instrument sounds? If so, then you must have already done the above.. However, just to avoid confusion, make sure the two Direct Monitor knobs on the interface are all the way off -- that way you'll know when you have the routing done correctly in GarageBand because you won't hear the keyboard's instruments until you do.

Since I don't know what 'buzzing' sounds like in this case I can't offer any specific suggestions, other than a couple of general suggestions.. If by 'buzzing' you mean the instruments sound distorted, then make sure the signal going from the keyboard into the interface is not too high [too loud]. If the level meter in the Audio track in GarageBand is too high [into the yellow or red] as you play the instrument before you begin recording, turn down the level controls (apparently labelled SENS] on the interface for the channel[s] you've plugged the keyboard's audio Outputs into. If by 'buzzing' you mean crackling or intermittent, check the audio cable connections for loose or broken cables [try a different set of audio cables].