This signal typically originates from a source with a fairly large impedance. It then translates this signal into a large-level signal. This large-level signal may also drive speakers with low impedance. Depending on the type of amplifier, one of several kinds of elements are used in order to amplify the signal like tubes and transistors. A few decades ago, the most common kind of audio amplifier were tube amps. Tube amps employ a tube as the amplifying element. In that way the low-level audio is converted into a high-level signal. Aside from the original music, there are going to be overtones or higher harmonics present in the amplified signal. This has put tube amplifiers out of the ballpark for many consumer products. Class-A amps have the smallest distortion and usually also the lowest amount of noise of any amplifier architecture. To improve on the small efficiency of class-A amps, class-AB amplifiers employ a number of transistors that each amplify a distinct area, each of which being more efficient than class-A amps. Because of the larger efficiency, class-AB mini amps do not require the same amount of heat sinks as class-A amplifiers. Therefore they can be made lighter and cheaper. The switched large-level signal has to be lowpass filtered in order to remove the switching signal and recover the audio signal. Both the pulse-width modulator and the transistor have non-linearities which result in class-D amplifiers having larger audio distortion than other types of amps. Newer amplifiers incorporate internal audio feedback in order to reduce the level of music distortion.