Noise sensor and volume control

[sonix]

A freind of mine is trying to find a way to control the volume on his TV depending on the ambient noise. I know you can use IR transmitters to actually put the volume up/down, but how can he trigger this?

Can anyone think of a possible solution?

Thanks.

snx

[Otto-Mate]

Re: Noise sensor and volume control

I'm sure it could be done.

He'd need some controller to do the logic, a PC or a dedicated controller with I/O like HomeVision.

Sound sensor linked to the controller, with the controller sending the up/down IR signals based on the thresholds set by the user.

Without descrete level controls on the TV though you'll be in trouble. If the user changes the volume level, then the system tries to increase to a pre-determinded level by sending X Volume Up commands for example, the system will soon get out of sync.

M.

[toscal]

Re: Noise sensor and volume control

This is not as easy as it sounds.
I know some comercial amplifiers that are used in bars have this ability, but they are not 100% perfect. In one bar I was in every time the cash register was closed the volume went up for a few seconds.
What you need is some kind of AGC circuit. see these sites for more details http://www.answers.com/topic/automatic-gain-control

http://www.elecdesign.com/Articles/Index.cfm?AD=1&ArticleID=6272

Another way is to invert the background noise and insert it into the sound being playedback. Very similar to the way noise cancelling headphones work.
This site is a bit technical but quite interesting http://www.prosoundweb.com/install/s...2/interact.php

[sonix]

Re: Noise sensor and volume control

Thanks for all your input. I'll pass ont he replies to him.

I'm thining that the firs step would be to write some sort of software that monitors the sound levels from a microphone, or even have two microphones, one measuing the ambietn noise, adn the other the volume from the speaker...

You could then in theory use there diffence in the two volumes to try and keep the souds relatively the same.

anyway, i'l let you know if i give this a go, might nto be worth it really.

snx.

[Milesy]

Re: Noise sensor and volume control

I dont think you could really invert ambient noise in that way toscal... the TV noise will surely become *part of* the ambient noise as well including its reverbs etc... so you could end up cancelling out the stuff you want to hear as well as the stuff you dont want to hear and get that messed up phasing sound that you get.

Again.... If you are measuring background ambient in an open space (ie. a living room how are you going to seperate that noise from the TVs sound?

i.e controller hears noise and increases the tv volume, your controller than hears more noise and increases the volume again? sounds like a recipe for madness

[TimH]

Re: Noise sensor and volume control

How do car radios do it?
I've been in a few cars where once you've turned the radio on and set the volume, it goes up and down according to how fast (?) you're travelling.
Is it a speed sensor, or some measure of cabin noise that does it?

Tim.

[toscal]

Re: Noise sensor and volume control

The way it works is that the sound from the TV is directly fed into, say the black box, this is then subtracted from the ambient noise. So what is left is just ambient noise. This is then inverted and added to the tv sound output. Now this has to happen in real time.
The other way which is not quite real time is to average the ambient noise over a few seconds and work out the max volume of this and then increase the TV volume by this amount.

Speed related volume controls do it a variety of ways. I had a head unit which I fitted to my old car which would increase the volume as I went faster. I think this just looked at a certain frequency range and as this increased it would increase the volume a by a certain amount. I do know some systems are linked to the actual speed of the car.