First, what is NAS? According to Wikipedia, NAS is “a file-level (as opposed to block-level) computer data storage server connected to a computer network providing data access to a heterogeneous group of clients”. OK, so it’s a server that provides files to a computer over the network.

Another way to think of it is as a virtualized hard disk. An application running on the computer is probably not even be aware that the file storage it is accessing is elsewhere on the network.

By these definitions, I like NAS. What I don’t like is what “NAS” has come to mean when you buy a consumer-grade hardware/software “NAS”. Not to pick on any particular manufacturer but I’ll use Synology as I’ve owned a couple. I guess I have four issues with them:

• Cost/performance. For the money, these devices come with pretty low-performing CPUs and low amount of RAM. A “powerful” CPU in this world is a low end Celeron.
• Bloat. The original notion of “NAS” has been bloated to the point where these things have their own desktop and include their own package manager(s) that you can use to install all kinds of stuff… It looks great until you install some things and find out it doesn’t work that well or is hard to configure.
• RAID/poor scalability. I suspect the traditional RAID in the typical 4-drive consumer NAS has had its day. When you run out of space, you have to buy a set of new higher-capacity drives and… throw the old ones away.(*1) If a drive fails, the actual process of rebuilding the array is the most likely time that a drive will fail! (And if it does, your data is toast.)
• Reliability/single point of failure. Doesn’t matter how many drives you have, you still have only one power supply (remember: consumer-grade NAS). If that fails, no data access. That’s how my last Synology went, and why I won’t ever buy another.

(*1) Admittedly Synology did have an improved solution to this, their Synology Hybrid RAID. But you still have to replace at least two of the drives when you run out of space.

So what’s a better way – directly attached storage? No. I like networked storage. But I think these days, we need to think of networked services, of which storage is just one part. Point by point:

• Cost/performance. Almost anything is better. But for storage, an ODroid HC1, HC2 or H2 has loads more bang/buck, and can easily be set up as a dedicated file server. (There will be loads of other examples, these are just the ones I use/am familiar with.)
• Bloat. Start with a basic Linux server OS and add just the services you need. Don’t try and shoehorn all your networked services onto that poor little CPU in a NAS.
• RAID/poor scalability. 1. Use realtime sync to mirror your files across multiple machines. If one goes down, your files are all there on another machine(s). 2. Have another storage node on the network and write to it daily with a snapshot type of backup system. 3. Use a distributed file system like MooseFS, one or two drives per node. If you need more storage, add drives instead of replacing them!
• Reliability/single point of failure. One drive per node gives maximum power supply redundancy!

Not long after I purchased my ADI-2 Pro, RME released the “DAC only” version. It felt it worth a brief comparison. Here is the block diagram of the ADI-2 DAC:

As you can see by comparing to the block diagram of the ADI-2 Pro, the ADI-2 DAC is a much simpler device! Compared to the ADI-2 Pro, it is missing:

• Analog inputs
• The second pair of analog outputs and associated processing (i.e. Phones 3/4)
• Balanced headphone drive
• Digital outputs
• AES/EBU digital input
• Multichannel USB
• Rack-mounting holes

However, it gains:

• A dedicated IEM amplifier
• A remote control
• Incremental improvements in the internal clocking and analog output stage (these are now, I believe, in the currently produced ADI-2 Pro, which has received a name change to “ADI-2 Pro FS“.)
• Bass/treble and loudness compensation runs at 352.8 and 384 kHz sample rates
• An “auto-dark” mode
• Audiophile feet

There are some things that are just different:

• The unbalanced 1/4″ TS output jacks have been replaced with RCA jacks.
• The hardware reference levels are lower and uniformly spaced.
• The hardware reference levels on the unbalanced outputs are 6 dB lower than the balanced.
• The front panel is black instead of silver.

A dip like that is hard to remove – you can’t EQ it, as then the off-axis response will have a peak in it. Using Edge, I came up with a baffle for the Neo3; this is a quick prototype:

Prototype Neo3PDR Baffle

The on-axis response is shown in purple in the curve below. It’s not flat but it’s easy to EQ – the EQed response shown in green. I haven’t measured the off-axis response yet – that will tell if having a baffle this shape is any improvement. At the least, the baffle lifts up the bottom end, making the tweeter strain less with a low crossover point.

New Neo3 PDR tweeter baffle measurements, on-axis, with and without EQ

Update April 16th 2012

Here is the off-axis measurement (with no EQ). In the frequency range from 3-10 kHz, the frontal lobe is wider than with the ideal dipole, but as you can see it still behaves like a dipole with a distinct null at 90 degrees. (And this is not intended to be a 100% precise measurement, the mic position was determined with a tape measure and eyeballing the angle of the baffle.)