Audio buzz through Griffin iMic problem...

Gwailo

Gwailo

B.A. Economics (Hon)
Hi,

You might be able to help, don't get scared away by the music equipment :)

I've got the following recording setup:

- Bass guitar
- Boss GT-6B (effects processor with analogue outputs)
- Bass Amp (Kustom 10W)
- Griffin iMic (Analogue-USB converter)
- Studio headphones

* Bass guitar inputs to GT-6B
* GT-6B outputs (analogue) to a) iMic (mono out), b) amp (head phone jack) and my headphones are connected to the amp.

Ok, now I noticed that when the Griffin iMic is connected to the computer and connected to the GT-6B I get a buzz through the system, which disappears when I unplug the iMic converter. I hear the buzz in the headphones connected to the amp.

My question: is there a way to filter USB connections, or, alternatively, filter the analogue side? I suppose I could build a band-pass supression filter, but I'd like an easier solution if I can find one.

I have a feeling what's happening is that the USB bus power is inducing current into the analogue side of the connection (i.e., the mic-in). Now, I can see how Griffin may have overlooked this since most microphones are passive and nobody would ever know (you'd never be able to hear the induced buzz on a dynamic microphone membrane, no matter how quiet :))

PS I don't know if the powerline ground for all my equipment is properly wired (i.e., if it's actually grounded). Hey, I suppose it could be a buzz over the ground wire through all my equipment, but then, wouldn't I get buzzed even if the iMic isn't connected?

Any help is great, thanks in advance!:p
 
A real possibility is that the GT-6b is creating the buzz that you're hearing. I own a GT-5 for my guitar effects, but I never record direct with it because it does have some noise. I wouldn't be surprised at all if it isn't the iMic. A good way to check it out would be to plug a portable CD player into the iMic and see if you still get the buzz. You shouldn't.

Matt
 
Hmm

I suppose that's possible, but because the noice disappears when I unplug the iMic, and doesn't reappaear when i plug in any other peripheral (i.e., short circuit in the jack) I'm a little sceptical.

But thanks for the contribution! :p
 
So you hear the buzz even when the iMic alone is plugged in, without any device connected to the line in jack? Also, if you record using the iMic, and play back the recorded audio later (after having unplugged the iMic), do you still hear the buzz?
 
I record audio with an iMic, both from a Sony cassette deck and from an Onkyo receiver. No buzzing heard here.

(Aside from input being somewhat overly bright and loud, I have no criticisms of the iMic, especially for the price.)
 
Ok, I'll take a closer look at my whole setup.

Thanks all! Your help was appreciated :)
 
I saw your thread and had to respond because we have similar set ups. I have an iMac 700 and the iMic. Once you plug an instrument in, you are going to get hiss, even with humbucking/humcancelling pick ups because it's the nature of the beast. What enhances that 60 cycle hum is plugging into an amplifier. You might try playing your bass direct into your computer and recording, then affecting it digitally with the plug ins that come with your recording software. I have a bare bones system (SoundEdit 16 bit) and when I play direct there is very little, if no, hiss introduced to the recording.

Most effect boxes add hiss unless they are rack mounted. The stomp box variety seem to have less shielding and hiss protection than a $300 and up rack mount processor.

Do you have a website with samples of your recordings? We could share notes.

Hope some of this helped!
 
Thanks for your reply! I don't hvae a site up yet, and I'm still quite amateur, but I'll let you know when I have something. Do you have a site up?
 
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