sentences:  Apart from putting the DAC stages into a separate case, the transport was mounted on a lead beam suspension to reduce disc reading errors; a unique audio stage offered the choice of six alternative playback filters; and the digital-to-analogue conversion was performed by six matched DACs to give linearity down to −120 dB at a time when most players were only linear down to about −94 dB.The CD1 soon became a three-box player with the arrival of a Quality Assurance Module, which monitored all the errors on the disc and quantified those that could not be corrected.This proved popular with many audiophile enthusiasts and also with specialist record companies around the world.