A Quiet PC without spending hundreds on noise reduction.

[arkay]

Ok guys,

Had a bit of a brainwave the other day. I'm sure most of you would've seen or heard of noise cancelling headphones. They work by having microphones on them that are continually recording ambient noise outside the headphones, inverting the frequency and playing that back through the headphones. Thereby cancelling out the noise.

Seems odd that more noise can result in less but it does.

Now. The thought goes:

- Fans and drives and everything in a PC result in fairly low pitched whirring (ambient) noises.
- Theoretically the same noise cancelling process should work if.
- You place a good quality microphone in or near the PC, sample the sound and
- Invert the sounds and play it back either via the PC internal speaker (probably not good enough) or via some small top quality speaker mounted inside the PC.

The only requirement is that it can sample/invert and playback fast enough so as to cancel the noise coming from the machine.

I can see two ways of making it work.

1. Use the PC's soundcard itself and write a small app that does nothing but record and cancel the PC's noise or
2. Make a custom circuit with microphone and speaker that can be mounted internally to the machine.

I'd be interested to hear what peoples thoughts are. The difference here is that with noise cancelling headphones the sound is sampled external to where the inverted noise is played back (within the headphones)..

I believe it should be possible though. If it works we won't need to be worrying about noisy components at all

I tried this yesterday with cooledit pro and a microphone but because my speakers are not located close to the PC I didn't really get great results.

If anyone can think of an easy way to set theroy into practise I'd be interested to hear about it.

A bit of a search on the net reveals that I am not the first person to think of this however no one has yet successfully done it. There are circuits on the net but unfortunately at the moment I have neither the time or the ability to etch a board and solder it up to try.

Open to discussion!!

Cheers,
Arkay.

[schmeg]

Excellent idea arkay

I actually remember seeing something on TV quite some time ago about a car that did this (ie. had a microphone under the bonnet recording the engine/road/ambient noises, and (I think) feeding the cancellation through the car audio system - resulting in silent driving. I'm pretty sure it actually worked (from memory) too.

Also Blaupunkt steroes have all kinds of spiffy circuitry, I think one of their models actually does this (but from a microphone inside the head unit).

[schmeg]

I think this is what I was thinking of - not quite what you'd need :/

http://www.blaupunkt.com.au/technology_7.asp

[arkay]

Yep, that's basically it. I'm thinking that you could also transfer the inverse wave out of whatever speakers your using with media center. It should cancel the sound of the PC altogether. Only have to get the volume levels correct and you're done

Just need to find out how to use the Mic input on the PC to sample and invert the wave.. It should be a pretty basic application. Could be one of the most useful plugins yet for MCE.

Maybe I should've kept my mouth shut

Hehe..

Cheers,
Arkay.

[schmeg]

Originally Posted by arkay

Maybe I should've kept my mouth shut

*strolls down to the patent office*

[arkay]

Hehe..

Just had another thought. Most of us are using stereo as a minimum or full surrond systems. With the right micing you should be able to center the inverse wave noise right at the same location where your PC sits..

i.e. If your PC sits to the left of your tv between the center and left speakers then you'd want to "project" the cancelling noise there.

Gonna have to read up on audio programming in windows... I just know it's going to be more ugly than I'd like though

Cheers,
Arkay.

[simbot82]

Sounds spiffy. hmmmmmmmm get this baby working and negate all those silent PC parts manuacturers out there i wonder could be worth thousands at least

Oh you guys still there

Sounds intriguing Arkay, the perfect tonic for a bloke in need of recuperation, hours at the computer screen

[schmeg]

Hmms ... http://www.mp3car.com/vbulletin/showthread.php?t=22132

[arkay]

the problem with the LMS algorithm is that for systems where
eigenvalue spread is large, the convergence rate can be slow.
filtered-x algorithm is one of the family of self-normalizing lms like
algorithms invented to solve this eigenvalue spread dependency.

Yeah.. Makes perfect sense I'll just code that up now then shall I

Think a bit of research might be necessary!!

Cheers,
Arkay.

[schmeg]

Yeah ... me and algorithms used to be friends ... not no more though

We need to find a uni that'll give this to a comp. sci. student for a project

[arkay]

Hahaha... Naaaah. I used to be a Comp Sci student... I wouldn't have given anything like this to me back then... Though the alcohol may well help understanding it all

Cheers,
Arkay.

[simbot82]

Well there goes my retirement plan. Back to the cricket then.

Good luck with the research arkay, and don't spend too much time sitting at the screen

[schmeg]

Originally Posted by arkay

Hahaha... Naaaah. I used to be a Comp Sci student...

Yeah me too - who knows, maybe they're more advanced now...