RedNet is no exception to Focusrite's philosophy that 'sound is everything'. In fact, Focusrite took this philosophy one step further with RedNet, a technology which embodies the company's most advanced A-D/D-A conversion to date along with rock-stable JetPLL clocking and premium 'red' analogue circuitry.
With every design detail meticulously engineered, RedNet is a step above its I/O competition, providing some of the most transparent and pristine audio quality available – with the added benefit of the systems' revolutionary networking capabilities.
RedNet designer Simon Jones sat down with Richard Elen to discuss the technology behind the sound.
Using the same conversion method throughout all of the RedNet analogue units, Simon worked on getting one to the required level of quality, and then used the same ADC approach across all the units. This not only resulted in the same level of performance across all the units, but also ensured the delivery of similar sonic attributes.
With any digital/analogue system, a balance has to be struck between sonic quality and the noise floor of the system. Simon's focus was to ensure that the best tradeoff was achieved. One problem with high quality A-D conversion is the harmonic distortion at input levels above -6 dBFS. Below that level, most systems are fairly similar, but because of the way ADCs are driven, there can be problems at higher levels if care is not taken in the design. This problem can be avoided by paying close attention to the types and quality of analogue components used in the driving stages, to ensure that they don't add any harmonic distortion and to keep the sound clean.
The circuit board layout is also critical in converter design and again, once the layout was confirmed, a similar layout was used in all the RedNet models. “We used multi-layer boards, and gave a lot of thought to where the current flows and how it flows, around both the analogue and the digital sides of the converters", says Simon, “ensuring that the analogue and digital parts don't interfere with each other".
A rather unique feature of the RedNet conversion design is that the signal remains balanced throughout the audio path. This provides a purer signal path and keeps the noise floor down, avoiding balancing and then unbalancing the signal as it passes through the unit. Modern high-quality converter chips accept a balanced input directly, so staying balanced from input to converter makes a lot of sense. “Traditionally, the signal comes in balanced, gets unbalanced, processed, and then rebalanced," Simon comments, “But in RedNet I took the decision to remain balanced from start to finish" resulting in superior audio quality.
Naturally, the RedNet analogue units employ the DC coupling approach throughout the conversion stages to secure a flat frequency response.
The overall essence is one of attention to detail rather than the “special sauce" approach that characterised some earlier approaches to digital conversion. There is nothing special about the dither used, for example – by far the most significant source of noise is semiconductor noise in any event – and no noise shaping is used. “Noise shaping masks problems, essentially", says Simon. “When the design is right, you don't need to do any."
The Dante system tends to be used in closed systems such as PA systems, where it doesn't need to communicate with external devices, but this is not the case in modern audio applications where a great many digital devices may need to be brought into play. As a result, the Dante system needed to be upgraded to meet Focusrite's specifications. Discussions with Audinate resulted in Focusrite's decision to augment the original Dante system with a highly stable clocking system to make external interfacing a reality.
The obvious choice, as it is already employed successfully in Focusrite equipment, was JetPLL®. The use of JetPLL ensures that whatever the quality of a clock coming in from outside into the RedNet system, it would be cleaned up, resulting in minimal jitter in the audio band. In addition, it would also clean up jitter in network clocks. Thus when the peer-to-peer timing protocol (PTP) clock is distributed around the system, because each unit has a JetPLL clock, its level of jitter becomes irrelevant. “What we made sure," Simon notes, “is that one of the major issues that digital systems have, namely audio jitter, was knocked on the head."
Focusrite have brought together several areas of their expertise to create the RedNet system – a whole that is greater than the sum of its parts. By taking the proven excellence of the Dante Ethernet-based audio networking system and combining it with impeccable component selection, optimised multi-layer board design, and analogue and digital design that is second to none, RedNet delivers the best possible audio quality – alongside the most flexible capabilities in the industry: RedNet by Focusrite.