keyboard line out and griffin imic incompatibility?

Make sure the little switch on the iMic is towards the mic icon, this puts it in Line-Level mode (the other was is Mic-level)

Also, make sure the keyboard volume is very low or even all the way off, then slowly bring it up (headphone-level is hotter than Line-Level, so start of slow)

Here are a few interfaces, among many:

http://www.thehangtime.com/gb/gbfaq2.html#interfaces

--HangTime [Will Compute for Food] B-|>

The iMic is a very inexpensive interface. As I recall the Griffin FAQ was rather humorous, there were questions about the quality of the PREs and the answer were "It costs $35!". IOW, you're getting what you paid for.

I used an iMic for several months and rather enjoyed what I was able to do for barely a handful of bills.

However when we later moved on to a high quality (and high priced) interface I was blown away by the difference.

The noise floor on the iMic is rather high, there is always a bg hiss. Using a high quality interface, if there's no noise in the room, there is no noise on the recording.

So while I'm really guessing since I haven't heard your recordings, I'd say "yes", if you want top notch recordings, you'll need to buy a better interface.

--HangTime [Will Compute for Food] %-|>

tell me if I'm on the right track on the
following theories (I don't know if the following are TRUE):

I'll do the best I can...

1) The quater-inch headphone output from the Yamaha
keyboard is neither "balanced"

Correct, the headphone-out is not balanced. A balanced output uses 3 wires, a graound, a hot, and another hot that's 180° out of phase with the first. This is a neat trick in that two signals 180° out of phase with each other cancel each other out sp you get zero signal. In the case of a balanced out if noise is introduced, it is in phase on both cables. On the other end when the signal on the out of phase wire has its phase flipped, your original signal is now in phase on both legs, and the noise is 180° out of phase with itself, and thus is canceled out.

nor impedance matched
to the Griffin iMic.

The impedance is not a problem here. As I understand it, the headphone-out is High Impedance, and so is the iMic's In.

(I'm using a 1/4" to 2.5 mm
converter cable). I am possibly getting radio
interference (I DID get a local radio station when I
touched the plug right!!) and degrading the signal
because of these two issues.

Possible. A Low quality cable and or adaptor could offer an entry point for noise.

2) It may be necessary to put the signal from my
keyboard's headphone jack into a DI (direct box) to
get impedance matched to mixer levels - the levels I
assume the Griffin iMic expects.

No, this shouldn't be true. A headphone-out is actually much hotter than a Line-In, so the level should be able to offer more than enough signal, and the impedance is matched.

3) I'm HOPING that a high quality audio-to-USB (or
firewire) input box can perform the job of the direct
box.

It could, but the weak point I see is that you're stuck using a headphone-out instead of a Line-Out. I don't think a DI box is going to help any in comparison.

Hmmm, I just glanced at your computer list. Doesn't the iMac have a Line-In jack? Have you tried skipping the iMic and going straight into the iMac?

Finally, if anyone can give me the list of equipment
in order from a keyboard to Garageband

I think it could be Keyboard -> Mac

Other combinations would just be sticking an interface between the two (Keyboard->interface->Mac)

only has MIDI IN, MIDI OUT and PHONES/AUX OUT),

I'm intrigued that the jack is labeled both PHONE a well as AUX. An AUX out is generally a Line-Level out.

1) If it's not an impedance issue, but a signal
balance issue, then my Sony stereo mic (with its 2.5
mm jack, three conductors) doesn't look balanced
either (since stereo would require 5 conductors in a
balanced system, right?) but it doesn't have this
problem. Does that lead us to a shielding issue
somehow?

The mic is almost certainly a high impedance mic, so I'm sure it's not a Lo-Z/HiZ thing. Shielding is a possible cause for noise entering the signal chain, yeah.

2) The imac flatpanel does not have a direct audio in
(a disappointment to a lot of us Mac users when it
came out).

Which model, the Lam-Neck or the newer Looks-like-an-LCD-and-nothing-else?

I'm stuck with audio-to-USB or
audio-to-firewire as far as I know. That said, what
did you mean by "sticking an interface between the
two (keyboard and computer). You mean like the iMic
or the, for example, the MobilePre USB audio
interface?

Yes, the iMic (and MobiePre) are both interfaces.

I'm heading that direction at this point.
I'm just concerned that another interface will handle
the PHONES/AUX OUT just as badly because it's not a
standard signal for sound recording (but in fact
intended to drive headphone speakers). Is there a
reason to believe it will handle the signal better
than the iMic? Or should I be getting a keyboard with
a "proper" line out?

A MobilePre will almost certainly have higher quality A/D converters, but it's really hard to say for certain if it'll help.

Do you by any chance have a sample of your playing somewhere online? Could you upload a small sample somewhere? Perhaps if I can hear exactly what the issue is I can make a better guess.

If you do decide to look for another interface, obviously do some research, but try to find a store (real, or online) that has a liberal return policy.

I'm done bugging you now. Thanks!!

No worries, I enjoy helping out when I can. Musicians are special, and music is magic --Hang

2) The imac flatpanel does not have a direct audio in
(a disappointment to a lot of us Mac users when it
came out). I'm stuck with audio-to-USB or
audio-to-firewire as far as I know. That said, what
did you mean by "sticking an interface between the
two (keyboard and computer).

Weird... Are you SURE?? My 17" flat panel G4 iMac (with USB 2.0) has a line in.