OPPO has just released the HA-2 DAC and Headphone amplifier. It is sized to use with your smart phone's digital output using a USB-micro-to-USB-micro cable. With a Sabre Mobile DAC, the HA-2 will decode up to 32/384 PCM and DSD256 music stored on your phone (you will need a downloadable app).
Computer audio is all the rage now, with many people moving their entire digital collections to music servers, and the laptop taking the place of the CD player in many systems. The technologies behind USB DACs have evolved rapidly to where the interface is now on the same level as Coaxial or Optical interfaces. One area that hasn't been addressed as well is the portable audio market, as most USB DACs are rack-sized components that require a wall power supply. This is certainly not a convenient option for those of us that want high-resolution audio on the go.
Most audio component manufacturers have a DAC in their product lineup, and NAD is no exception. However, the NAD M51 is unusual in that it takes the incoming digital PCM bitstream and converts it directly to a PWM bitstream, which is then fed directly to the output. The idea has been around for about a decade, but the technology for implementing it was not fast enough in those early days. Now, with modern technology and techniques, NAD has produced what they call a "Direct Digital DAC", where the digital signal does not go through digital to analog conversion in the normal sense, but converted to PWM at 844 kHz sampling, with 35 bit word length. As you will see with the bench tests, the results are quite amazing, and the price is very affordable.