Sure, NAD's M51 is an exceptionally musical-sounding digital-to-analog converter, but it's much more than that. It's also a versatile digital preamp with enough inputs to handle all of your digital music sources: disc players, network music players, and even your computer. What puts this DAC in a class by itself is NAD's acclaimed Direct Digital technology, which uses immense processing power to transform digital bits into music that's warm, involving, and lifelike.
How NAD's Direct Digital technology works
NAD's powerful processing engine has exceptional speed and accuracy compared to typical DACs. To get technical for just a moment, the M51 re-samples the incoming pulse code modulated (PCM) signal and converts it to a pulse width modulated signal (PWM) with a sampling rate of 844kHz. One big benefit of converting PCM to PWM is that it completely eliminates any timing errors, known as "jitter," in the incoming signal. That's reflected in the M51's vanishingly low numbers for noise and distortion.
Sound that expresses the spirit and soul of your music
Specifications matter, but they can't describe the energy, presence, and life that the M51 restores to your music. Thanks to this DAC's extremely high clock speed, sophisticated filters can be used to remove nasty digital artifacts like ringing, while maintaining the nuanced dynamics and tonal purity that will make even familiar recordings sound fresh.
All the right connections — including HDMI
The M51 offers an array of digital inputs, plus high-quality analog outputs including balanced XLR.
The M51 is uniquely equipped to dramatically improve the sound quality of all your stereo digital music sources. It has a coaxial digital input, which is great for connecting a CD or DVD player, or a Sonos® Connect player. And an optical digital input is the ideal hookup for your HDTV, Apple TV®, or game console. In addition to these common inputs there's an uncommon balanced digital XLR input that provides an ultra-low-noise connection when used with a compatible high-end CD transport.
A Type B USB port makes it easy to feed the output from your computer into the M51's superb DAC, bypassing your computer's sound card to yield much higher quality sound with stored or streaming music files, including high-res files with sample rates up to 192kHz. (Free USB driver download required for Windows® PC playback.)
Plus, the M51 is the first unit of its kind that we've seen to offer HDMI connections: two inputs and one output with video pass-through. This gives you access to the high-quality 2-channel soundtracks found on nearly all Blu-rays and DVDs. Many symphony orchestras and some specialty music labels are also releasing high-res audio recordings on Blu-ray or DVD.
Praise for the NAD M51 from Stereophile
"The M51 projected a rich, lovely sound that wasn't too forgiving, which was to its credit. I like to hear a recording's technical warts, if any."
"I prefer DACs that reveal as much as possible about what was captured on the tape or in the digits, and couldn't care less about adding a rose-colored tint to dodgy digital sound. In this regard, the NAD M51 succeeds with a wonderfully detailed and revealing sound best described as honest, with a friendly smile. And it was a pleasure to listen to. "
— From Jon Iverson's review in Stereophile, July 6, 2012
Read the full review
It's a versatile digital preamp, too
The M51 is a fully functional digital preamp with one of the world's best volume controls. NAD's 35-bit architecture makes it possible to have a DSP-based volume control that does not reduce resolution — even with 24-bit high resolution signals. In fact, all switching and volume control is done in the digital domain. The only analog circuit is the Class A buffer at the output of the DAC.
Note: input selection is available from the front panel, but volume can only be adjusted via the remote control.