 Loudspeakers are also required at various points in the audio processing chain to enable engineers to ensure that the programme is reasonably free from technical defects, such as audible distortion or background noise.The engineer may mix programming that will sound pleasing on the widest range of playback systems used by regular listeners (i.e.high-end audio, low-quality radios in clock radios and "boom boxes", in club PA systems, in a car stereo or a home stereo).