Re: [tuxdroid-user] Dedicated sound normalizer / multiplexer daemon

[Philippe T. <ph...@te...>]

Florent THIERY wrote:
>> Actually the 500Hz comes from the 2.4GHz signal which is pulsed at 500Hz (a frame is sent each 2ms, thus 500Hz).
>>     
>
> Would'nt a passive "passe-haut" filter remove it? (no idea how it's
> called in english :p)
>
> http://fr.wikipedia.org/wiki/Filtre_passe-haut
>   
Follow the link to the english page ;-)
And you'll discover it's called High-pass filter
http://en.wikipedia.org/wiki/High-pass_filter

But if you skip everything belog let's say 550Hz you'll miss a big part.
Think that the musical A ("la" en français) to tune instruments is only 
440Hz
(as well as the phone tone)

500Hz is just in the middle of the useful audio band that's it :-(

What you need is a notch filter:
http://en.wikipedia.org/wiki/Band-stop_filter
but getting a very narrow one is not that obvious.
Depends how good is the AVR on audio processing...

Otherwise analog ones are possible, starting from the very basic RLC filter:
http://www.everything2.com/index.pl?node_id=1391618&lastnode_id=0

Phil