To cancel noise... kinda like phase cancellation on purpose.

[kristian]

I had a thought today while i was sitting on the throne before school. Say you have a guitar track, and you have a 3 second intro of that wav file where you have a bit of hum from the loud/distorted settings on the guitar. This hum should be somewhat cyclical, ie in the USA 60 cycle hum. Could you take one cycle of this sound from the beginning of your wav invert the phase, and then place it accross your entire wav to cancel out the hum from the amp and just the hum from the amp? or am i just floating in the clouds?

 

[Blue Bear Sound]

Well, yes... in theory....

That's how some noise-removal plug-ins work - give them a noise clip and it removes all components of the signal that look like the clip...

Of course, it can't distinguish between desired freqeuncies around the noise level and undesirable ones, so that's where the theoretical application breaks down from practical application!

It depends on how complex the signal waveform is, and how different the signal is from the noise you're trying to remove. For example, removing a 60hz hum from a bass track may alos remove a lot of necessary low-frequency signal from the actual bass that you want to keep!

Bottom line is you have to try it - sometimes it'll work great, other times, not so great.

Bruce

 

[ausrock]

Bruce,

On the subject of "phase", but in the context of mics, if a console hasn't got a phase reversal switch, am I right in thinking that I can get around the problem by changing the wiring in a mic connector .........i.e; swap the red and black wires around on one end of the cable. Or is that too simplistic?

 

[kristian]

ausrock, i know for sure that that is one way to flip the phase if you don't have a switch for it. I was assuming that you would loose other freqencies. I bet that would make for some cool FX if you could think up clever ways of cancelling things out.

 

[ausrock]

Kristian,
Thanks for the answer. My Soundcraft console doesn't have "phase reversal" on the channels ........and I am thinking of making up a few short XLR-XLR phase reversal leads just in case I run into the need at any time. Just wanted to be sure that they would work OK.

 

[John Sayers]

Ausrock - a few phase reversal cables is a good idea BUT! make sure you label them boldly so as to distinguish them from your normal leads. We used to paint ours red. You must use them when mikeing under snare and when using a mike in the back of a guitar amp as the phase coming out the back of a guitar amp (open back) is out of phase to the front.

cheers
JOhn

 

[TexRoadkill]

You can always reverse the phase in your DAW by doing a Invert on the sound file.

 

[ausrock]

John,
I understand. Thanks for the input.

Tex,
Valid point, except I'm not travelling the DAW path. To my mind, computers aren't the "be all and end all" that some people would have us believe. Consequently, I am running an analogue console, dedicated H/disk recorder and my PC is only there to do burning on.