Impedance
in [Basics]
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From: John Popelish on 16 May 2005 23:21 Music Man wrote: > So what is the relation to frequency and capacitance John? The effect of capacitance (the ability of the capacitance to pass current per volt across it) is proportional to frequency. Pick any capacitance and this formula tells you the volts needed to drive 1 ampere through it. But volts per ampere are called ohms, so the formula is Xc = 1/(2*pi*f*C) where Xc is the capacitive impedance in ohms (or volts per ampere), pi is 3.14159, f is frequency in hertz, and C is capacitance in farads. > Could you explain on how audio signals are "expressed" in electronic > circuits. Either as a voltage that represents the signal or as a current that represents the signal. If a capacitor is in series with the signal, it passes it better as the frequency goes up. If the capacitor is between the signal and ground, it drains more and more of the signal to ground as the frequency goes up. > What is need to creat a clean signals?How resistors creat noise and add to > signal? Whole different subject. Resistors (the gas of electrons in resistors, actually) make noise just to be in thermal equilibrium with their surroundings much like gas molecules bang around just from thermal energy. Then when you pass current through resistors, it bumps and bangs and surges a bit, because the current is composed of finite charges, not a smooth fluid, adding a different spectrum of noise to that from the unbiased resistor. You should probably read a bit on this and come back with questions. http://zone.ni.com/devzone/conceptd.nsf/webmain/8DE42E13BD089D8B86256816006545CD?OpenDocument > What I mean is why would a Neve mixing console sound better than a cheapo > desk. There are noisy resistors (noisier than can be explained by thermal noise), low quality capacitors that pick up vibrations and change capacitance as the signal voltage swings, opamps that are noisier or quieter, well shielded and poorly shielded designs, etc. Understanding all that, including the etceteras can take a lot of study and experience.
From: Rich Grise on 17 May 2005 10:36
On Tue, 17 May 2005 00:59:08 +0100, Music Man wrote: > So what is the relation to frequency and capacitance Xc = 1 / (2 * pi * f * C) Xc = capacitive reactance in Ohms f = frequency in Hertz C = capacitance in Farads. Cheers! Rich |