Audio data is stored on CD as 16-bit words. It is the job of the digital to analogue converter (DAC) to convert these numbers to a varying voltage. Many DAC chips do this by storing electric charge in capacitors (like water in buckets) and selectively emptying these buckets to the analogue ouput, thereby adding their contents. Others sum the outputs of current or voltage sources, but the operating principles are otherwise similar. A multi-bit converter has sixteen buckets corresponding to the sixteen bits of the input word, and sized 1, 2, 4, 8 … 32768 charge units. Each word (ie sample) decoded from the disc is passed directly to the DAC, and those buckets corresponding to 1’s in the input word are emptied to the output. To perform well the bucket sizes have to be accurate to within +/- half a charge unit; for the larger buckets this represents a tolerance tighter than 0.01%, which is difficult.
Audio data is stored on CD as 16-bit words. It is the job of the digital to analogue converter (DAC) to convert these numbers to a varying voltage. Many DAC chips do this by storing electric charge in capacitors (like water in buckets) and selectively emptying these buckets to the analogue ouput, thereby adding their contents. Others sum the outputs of current or voltage sources, but the operating principles are otherwise similar. A multi-bit converter has sixteen buckets corresponding to the sixteen bits of the input word, and sized 1, 2, 4, 8 … 32768 charge units. Each word (ie sample) decoded from the disc is passed directly to the DAC, and those buckets corresponding to 1’s in the input word are emptied to the output. To perform well the bucket sizes have to be accurate to within +/- half a charge unit; for the larger buckets this represents a tolerance tighter than 0.01%, which is difficult. Furthermore the image spectrum from 24kHz to 64kHz must be filtered out, requiring a com