Speakers feeding back while recording in garageband - HELP!

So basically I am having a massive problem.

Just got a Mac, it is an iMac G5 PowerMac8,1 1.6GHz 1GB RAM etc

Running iLife 08.

I have just started to use garageband. I started recording with my electric guitar, plugged my cable into the 3.5mm line in mic socket and obviously the other end in the guitar.

I selected a guitar effect with a distortion sound and record. When I play back I realise there is this infernal din coming out as well as what I've played all the way through the track.

It actually does this with every effect and on every instrument I plug in with varying degrees on velocity and it is so bad you can not use 75% of the effects on a real instrument recorded track which kind of defeats the point of have a recording software.

On further inspection, turning on the monitor setting on i realise this sound is contant the whole time even when the guitar is not even plugged in and I have no idea why.

I have set my audio settings as they should be, copying numerous tutroials but I still get this feedback buzz noise sound.

Can someone please help me!

I will list my settings here:

System Preferences: Sound, Input = Line In Audio line-in port
Garageband Preferences: Audio/MIDI = Audio Output = System Setting or Built In Audio (either one makes no difference), Audio Input = System Setting or Built In Audio (again, either one makes no difference)

I have made a youtube video which you can find here:
Mac speaker feedback issue in garageband - YouTube

SERIOUSLY CAN SOME PLEASE HELP! I have discovered it does this even when the cable is not plugged in and the monitir is on!

I just watched your vid - thanks to Robducky. Does this noise occur under any other circumstances? I'm not completely convinced it's feedback - but it's hard to tell from the video. I'm wondering if it could be noise induced by another source - either internal or external.

You're using wrong connector that's why iMac didn't turn off internal Microphone

More info? This is my reply to your old topic last week.

Ken Ardency said:

Normally it shouldn't act like that. The internal mic should disable automatically whenever line in is plugged with right type of connecter.

The only reason that your iMac didn't disable internal mic because you use 1/8" TS to 1/4" TS adapter. The 1/8" TRS input jack of your iMac didn't detect all three-conductors (Which are Tip Ring and Sleeve) that's why it didn't tell your machine to turn off internal Mic.

You'll have to get Y-cable that split from 1/8" Stereo TRS to 2 mono 1/4" TS Jacks. It looks like this.

Be careful don't buy headphone splitter. They look very similar to each other.

Or 1/8" TRS to 1/4" TS Cables like this is OK to use too. This is 'Monster iStudioLink Instrument Cable' cost around $26

Y-cable or Instrument Cable can be DIY but you should use high standard cables and connecters such as Canare, Mogami, belden, Neutrik, and etc... It's a lot better than cheap pre-assembled cables and cheaper than expensive cables such as belkin, monster and etc...

I've been using Canare cables with neutrik connecters in my studio for more than 10 years and all my cables still working fine.

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