Direct Stream Digital. A digital encoding format proposed by Sony and Philips used to record SACD albums. DSD samples an audio signal at a fixed rate (frequency) just as in the PCM method. However, instead of recording the volume or amplitude as an absolute number, as in PCM, the DSD method measures and records how much the volume has changed since the last measurement. If the signal is sampled fast enough, the amount of change since the previous sample would be very small. The proposal for DSD is for a sampling rate that's over 2 MHz (2 million times per second). At this high speed the changes in signal strength can be represented with one bit. DSD also compresses the data resulting in a 2:1 reduction. DSD will be able to provide a frequency response from DC to 100 kHz with a dynamic range of 120 dB.