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Removing hum


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This is probably a beginner's question, but I am a beginner.


I am trying to move my old vinyl record and cassette tape collection to my computer and from there to my iPod. I am using a Mac G5 computer. I am inputting into the computer using a cable that has two RCA plugs at one end to hook to the receiver output, and a small cylindrical plug to go into the sound input on the computer. I input using the Apple program GarageBand.


When I input a song from vinyl records, or from a cassette tape that taped from a vinyl record, I get an annoying hum, or buzz. I would like to eliminate that hum.


GarageBand has 29 filters, most of which have manual adjustments to them. Someone told me to use the AUParametric EQ, but could not tell me the settings to use. The three settings are


Center Frequency (20 to 22050 Hz)

Q (1 to 20)

Gain (-20 to 20)


Needless to say, Apple computer does not give me any instructions on what to use this for, or how to pick the proper settings.


There are 28 other filters, including AUDynamics Processor, AUFilter, AUGraphic EQ, etc. I do not understand any of them.


If there is an expert or hobbyist out there who knows, please tell me which filter to use, and what setting to use, to eliminate the hum, without doing too much damage to the underlying sound quality.


By the way, I am in the United States, and we have 60 Hz alternating current electricity.


I hope you can help me.


I may be asking too much, but when I input to the computer from a cassette tape, I get a very mild hissing sound. It is not nearly as annoying, but if someone knows how to get rid of that, that also would be helpful. But I am most concerned about the hum from vinyl records and would be very happy if I could learn an easy way to get rid of it.


Thanks so much.


Jim Lawrence


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Well, the way to fix the hum/buzz is not with the filters but at the source. It's almost certainly caused by the cabling linking your home turntable/cassette deck to your computer which is likely causing an earth loop. Trying to remove this by filtering will probably have too much effect on the sound quality for you to be happy with it. There are various things to try:


-If it is simple, single frequency mains hum, you COULD at least try the filter. Set the centre frequency to 60Hz, the Q to 3 or 4 (you can play with this) and the gain to -20. However, since you describe it as a bit of a buzz, I suspect this won't work.


-Try another cable in case this one is shorting somewhere. Phono/RCA connectors and minijacks are fragile and prone to this.


-Make sure the connectors at both ends are pushed all the way in but NOT touching the equipment chassis at either end.


-Plug the computer and hifi gear into the same socket (a multiway extension is fine). I know that, with American gear, it's not unusual for some things to have the third (earth) pin on the electric plug and for others not to. Assuming either or both the computer have an earth pin, make sure any extensions and sockets you use have the earth connected.


-If your turntable has an earth wire, make sure this is connected. You can try this either to your hifi amp (assuming you're using one) or to a screw on the computer chassis.


-If worst comes to worst, visit your local electronics shop and buy some "isolating transformers" (plus any necessary adaptor cables) for the link.


Finding an earthing problem can be trial and error, but it IS the only good way to cure your problem.


As for the hiss on the cassette tape, this is a case where your filters might work. I don't know "Garage Band" but many audio workstations have a feature called "Noise reduction". If you have this, then that's the one to try. If not, have a play with the filters. I'd suggest the Graphic EQ and start to pull down the gain on frequencies above 10 or 12 kHz (cassettes have little sound above these frequencies anyway. Again, find the best compromise between killing the hiss and making the music sound too flat and lifeless.



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