Capacitors in DC circuit?

Irrespective of the input source type, noises come in-circuit from external sources or by switching states of the components. In such a case, capacitors act as a reservoir and provide filtering while used in parallel as a filter capacitor. You will find such low to high-value capacitors in almost every circuit. 

But, blocking capacitors block dc and AC to be passed, in such case the audio circuit properly process the signal since audio signals are meant to be work entirely in AC.

When used in a direct current or DC circuit, a capacitor charges up to its supply voltage but blocks the flow of current through it because the dielectric of a capacitor is non-conductive and basically an insulator.  At this point the capacitor is said to be “fully charged” with electrons.
 

Used in a direct current or DC circuit, a capacitor charges up to its supply voltage but blocks the flow of current through it because the dielectric of a capacitor is non-conductive and basically an insulator. At this point the capacitor is said to be “fully charged” with electrons.

The capacitor is a component which has the ability or “capacity” to store energy in the form of an electrical charge producing a potential difference (Static Voltage) across its plates, much like a small rechargeable battery.

There are many different kinds of capacitors available from very small capacitor beads used in resonance circuits to large power factor correction capacitors, but they all do the same thing, they store charge.

In its basic form, a capacitor consists of two or more parallel conductive (metal) plates which are not connected or touching each other, but are electrically separated either by air or by some form of a good insulating material such as waxed paper, mica, ceramic, plastic or some form of a liquid gel as used in electrolytic capacitors. The insulating layer between a capacitors plates is commonly called the Dielectric.
Due to this insulating layer, DC current can not flow through the capacitor as it blocks it allowing instead a voltage to be present across the plates in the form of an electrical charge.