"Five Stars" from Hi-Fi Choice Magazine
Superior CD Player, DAC, and Digital Preamp
Designed to sit at the heart of a high-end digital music system, the Cambridge Audio Azur 851C is effectively three components in one. It's a superb sounding DAC, CD player, and digital preamplifier.
England's Hi-Fi Choice magazine gave the 851 C its top rating of Five Stars in the June 2012 issue. "A major advance on its already capable predecessor, the new 851C is a superb sounding digital hub that gives great hi-res and silver disc playback… The new player is remarkably refined, clean and revealing... a rich and sophisticated sounding machine that delivers remarkable tonal depth from a good recording."
"Deserving of Garish 'Buy Me' Stickers"
"No matter how challenging the music, the system kept a tight grip on proceedings while appearing calm and unflustered," notes John Bamford in his August 2012 joint review of the Cambridge Audio Azur 851C CD player and Azur 851A amplifier for England's Hi-Fi News magazine. "If ever there was a combo deserving of garish 'Buy Me' stickers on the fascias, it's these latest Azur components."
Not Just for CDs
Used as a high-end DAC, the 851 C allows a multitude of devices to be connected via its digital audio and USB audio inputs, including music streamers, digital iPhone/iPad docks and computers. Of course the 851C also offers stunning quality CD playback, and its uncompromised design ensures every last detail is retrieved from CDs.
Technical highlights include the highest specification twin D-to-A converters from Analog Devices, a 32-bit Analog Devices Black Fin DSP, and the very latest generation of upsampling technology from Swiss experts Anagram Technologies. This technological tour de force increases the quality of every music format, including low bit-rate MP3 files, CDs, and – best of all – uncompressed studio master content.
Cambridge Audio Electronics Engineer Sam Ellenby has worked on the development of the 851C for the last two years and believes it to be the most exciting product the company has ever created. "The 851 C produces almost no measurable distortion which is something that is gratifying as a designer and thrilling as a music lover. It's also the tiny details that make a real difference to the pleasure you get from using it. The simplicity of the user interface is something we're really proud of and proves that complex technology doesn't have to be complicated to operate".
The Adaptive Time Filtering Breakthrough
The 851C incorporates numerous advanced technologies, and key to its abilities is ATF2™ (Adaptive Time Filtering). This is the second generation of Cambridge Audio's highly regarded upsampling process, which was developed in conjunction with Anagram Technologies of Switzerland.
ATF2 intelligently interpolates all incoming audio data (such as 16-bit/44.1kHz from CD) to 24bit/384kHz through the use of a 32-bit Analog Devices Black Fin DSP (Digital Signal Processor). The ATF2 system applies polynomial curve fitting interpolation and incorporates a time domain model that allows data buffering and re-clocking to almost completely eradicate digital jitter, helping to ensure the best possible sound quality. A new ATF2 noise-shaping algorithm now also provides enhanced linearity with 24-bit sources.
Twin Analog Devices AD1955 DACs make a welcome return, having previously won praise in the 840C CD player. Here they are used in dual differential mode, and each channel has its own DAC to process information independently. These allow both left and right channel circuitry to operate identically, ensuring the 851C delivers fantastic soundstaging and stereo imaging properties.
It's a High-End DAC
With Windows PCs, the 851 C can accept USB audio feeds driverlessly at up to 24-bit/96 kHz resolution. And for the very best performance possible, a custom-designed Cambridge Audio Windows driver (available free from the Cambridge Audio support site) allows up to 24-bit/192 kHz operation and supports both kernel streaming and ASIO. (Apple computers already support up to 24-bit/192kHz USB transfer natively).
The 851C's Asynchronous transfer mode means that the audio data is not forced into fixed size packets to fit within a standard USB clock scheme – i.e. the data is now asynchronous to the USB stream. Instead, the 851C controls the flow rate and sets it for the actual audio sample rate being played. This dramatically reduces interface jitter across the USB transfer.
In addition, audio streamers and network music clients can be connected to the 851 C and upgraded via an SPDIF or Optical connection. The same applies to Blu-ray players, TVs and other audio sources with a digital output.
It's an Audiophile CD Player
Many CD players use drives designed for computers. Cambridge Audio avoided this approach due to the resulting noise and impurity and created its CD-only S3 Custom CD Servo™ drive. This audiophile design gives the 851C the ability to retrieve maximum digital information from CDs. Meanwhile, the Cambridge Audio-developed transport guarantees incredible rigidity, and the CD drawer itself has been designed to offer smooth operation.
It's Also a Digital Preamplifier
The shift towards digital music means that many people principally use digital audio sources such as computers, network streamers, and digital iPhone docks. The 851 C is the ideal audio hub for such scenarios since digital volume and channel balance functions enable it to be used as a digital preamplifier and connected directly to a power amplifier or active speakers.
These attenuation functions are completely processed in the digital domain through Cambridge Audio's proprietary DSP. This gives the highest quality of digital volume control as opposed to analog attenuation or digital bit reduction.
Selectable Digital Filter
The new ATF2 DSP features a selectable digital filter with three settings to suit your preferences and your particular system set-up.
The Steep Roll-off Filter exhibits strong attenuation of aliasing images outside the pass band (i.e. above 22.05kHz) at the expense of a little pre and post-ringing in the time domain. The Linear Phase Filter uniquely features 'constant group delay' which delays all audio signals at all frequencies by the same amount meaning all audio is fully time-coherent at the output.
Minimum Phase, meanwhile, does not feature constant group delay Instead, the coefficients have been optimized without feed-forward so that the impulse response exhibits no pre-ringing in the time domain.
All analog stages and filtering from the 851 C's DACs to output are also fully differential in nature. This fully balanced configuration largely rejects the already very low noise and distortion present in the DACs and filters and provides an unprecedented level of performance.
Balanced XLR Outputs – And More
Balanced XLR outputs allowing a balanced connection to the matching 851A are included in addition to conventional unbalanced phono/RCA outputs. In pursuit of the very finest sound quality, a high quality toroidal transformer is also used in the 851C. It ensures lower noise and less waveform distortion for quieter PSU operation. This equates to the purest sound with no buzz or hum that can be heard from cheaper transformers.
To ensure simple operation, a high contrast reverse black DFSTN display offers excellent feedback of the 851C's impressive features, which include CD-text support as well as the ability to rename digital inputs. In addition to these audiophile features, Control Bus Input/Output, IR Emitter Input and RS232 control are provided to make it easy to integrate this unit into custom installation systems. | 
