Here I review the Metrum Octave NOS Mini DAC. I cover some background on DACs, NOS DACs before getting into the review itself.
What exactly is a NOS DAC?
The problem with digital audio is that it can quite often sound too digital. Poorly implemented digital to analogue conversion can leave music sounding metallic / harsh / artificial – i.e. digital. The best DACs (Digital to Analogue Converters) manage to make digital sources sound more analogue or organic; in other words, more like a good vinyl system. Good sound should be free of digital artefacts that have arisen as part of the conversion process. If listening to music from a digital source (e.g. CD or streaming) leaves you feeling cold then one reason could be a poor digital to analogue conversion process.
Most DACs use a method called oversampling whereby harmful harmonic content in the stream is moved into very high frequencies where they are harmless. This harmful content is a by product of the digital to analogue conversion process. The technique of moving these to very high frequencies allows the sound to be smoothed over. The majority of DACs on the market use oversampling.
However there is a small group of hi-fi aficionados who believe that the oversampling process is to blame for the music still sounding digital – i.e. not live / organic. It is often said that the process of digitising and converting music back to analogue robs music of that “live” feel. These people therefore seek out NOS (Non-Over-Sampling) DACs as a means to make music sound better to their ears.
Fans of NOS DACs will say they sound warmer / smoother / more real than their oversampling counterparts.
Who are Metrum Acoustics?
There are several DAC chips in used today from brands such as Burr Brown (Texas Instruments), Analogue Devices or Cirrus. The majority of hi-fi manufacturers simply stick one of these DAC chips into their products, perhaps a small tweak here and there, then sell it on. Nothing wrong with that – two hi-fi products with same DAC chip can still sound very different because it is all about how you implement or configure it.
Other hi-fi manufacturers, such as Chord, use proprietary DAC chips that they have designed and built themselves. Metrum Acoustics also fall into the latter category. Metrum is a Dutch brand owned by All Engineering who produce a wide array of electronic products. After researching how to improve digital music, Metrum began to realise that the problem lay in the oversampling technique. This led them to go down the NOS route instead.
The problem here is that the big chip manufacturers no longer make NOS DAC chips – even brands like Chord use the oversampling technique. So Metrum looked outside the audio field and began to use what they describe as “high speed industrial grade chips”.
The Metrum Octave NOS Mini DAC
Here is one of the results of Metrum’s research: the Octave NOS Mini DAC. It comes in two small silver boxes: one box holds the DAC while the other is the power supply and they are connected by a short cable. Build quality is pretty decent – the boxes feel quite tough albeit a bit industrial. On the front of the DAC box are power and input switches. Alongside the switches are two LEDs: one indicating power, the other indicating no signal.
Round the back of the Metrum Octave is a single optical Toslink, single coax RCA plus stereo unbalanced RCA outputs. So this is a minimal DAC with limited inputs. This lends itself to be placed alongside something like a Sonos Connect, Apple TV, Apple Airport Express or a Bluesound Node – effectively boosting the performance of one of these products. In my system, I set up the Octave between a Bluesound Node and my Roksan Caspian M2 integrated amp.
Listening to the Metrum Octave DAC
The unit I had was previously owned, so I dispensed with warm up time. Instead I got down to the business of listening to the Octave. Right from the get go, I could see the type of sound that I was going to get from the little NOS DAC. The music was painted in a very smooth, neutral and even-handed way.
I wouldn’t say the sound is warm or bright – it sits somewhere in between as it should do. This is important because all a DAC should do is perform the digital to analogue conversion process in the most high quality way. Detail levels are pretty good, not the best I have heard, but certainly a step up over the DAC included within my Bluesound Node.
So does the Metrum Octave achieve what all NOS DACs should? Does it sound analogue? I would say yes, this is one of the least digitally sound DACs I have heard. Everything is nice / smooth / easy going with this DAC. I think its neutral nature makes it a good partner for a wide variety of hi-fi systems.
Who would use this DAC? As I mentioned above, I think the Metrum Octave makes a good partner for anyone who has a more mainstream device like Sonos, TV or even a budget CD player. It is small enough to be unobtrusive but capable enough to justify its presence on your hi-fi rack. Users of largely headphone based systems could also benefit here.
The review sample here is the Mark 1 Octave; Metrum have since released the Mark 2. The newer model drops the two box design for a single, larger, box, an improved power supply and better jitter reduction. There are said to be small performance gains to be had from the Mark 2. This version I review here can be had for a snip on the second hand market and as such is a bargain for those looking to get a little boost in their hi-fi.