[sdiy] Wanted: non mathematical description of the function of RC-filters

[Synovatron]

Hi Florian,

Check out the Analog Devices 101 whiteboard series on filters and other subjects at www.youtube.com/playlist?list=PL64A193CF0B94C5D3

Cheers
Tony

Sent from my iPhone

On 5 Aug 2013, at 21:57, Florian Anwander <fanwander at mnet-online.de> wrote:

> Hello,
> 
> I need your help for a kind of beginners introduction into filters. The readers have a quite basic understanding of electronics. They know that resistors and capacitors exist (only a few will know what they do), and they know the difference of AC and DC.
> 
> Now I am looking for a very(!) simple explanation of the working principle of a passive RC highpass and lowpass. There shall be no mathematics involved. I started like following, but I not really happy with it:
> 
> 'A filter works basically with the fact, that a capacitor transmits alternating current, but blocks direct current. An electrical audio signal is an alternating current. The lower the frequency the more the signal becomes similar to an direct current. If we keep the first statement in mind, then a capacitor acts basically like a high pass filter: the lower the frequency of an audiosignal is, the more similar it is to DC, and the more the capacitor will block it.
> To get a tunable filter one would need a tunable capacitor, but that its complex. A tunable potentiometer is much easier to build. So the RC filter was developed. It combines a resistor with and capacitor. The cutoff frequency can be regulated with the value of the resistor. The RC-Filter consists of two signal pathes: "through the capacitor" and "not through the capacitor". To get a low pass filter the signal path "through the capacitor" directs to ground. So high frequencies are grounded, while low frequencies are fed to the output. The high pass filter works the other way around: the signal path "through the capacitor" feeds the output, while the signal path "not through the capacitor" goes to ground, which meands low frequencies are suppressed.'
> 
> The original is written in german, and maybe my translation contains additional errors. But I think 95% are correct.
> I like this description until the point with the two possible signal pathes, but the final explanation of high and low pass does not suit me. Any better ideas?
> 
> Florian
> 
> 
> http://fa.utfs.org/
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