Now that digital audio is so common, not only for portable devices but also for home music systems, there are many devices coming onto the market to improve the quality of the sound for playing through high quality equipment. Whereas the original MP3 players were less than CD quality now it is possible to download digital audio files at much higher resolution than CD and even DVDs.
As the sound emanating from loudspeakers is analog, at some point in the audio reproduction chain the digital signal has to be converted to analog. It is most commonly done prior to the preamplifier. A Digital to Analog Converter (DAC) is a vital component in the signal chain and there is an increasing variety to choose from.