By Frederick Norén
Fifteen years after releasing their first D-A converter, Dangerous have brought out their first A-D. Was it worth the wait?
Dangerous Music have been making highly respected, mastering-grade outboard gear for almost two decades. Their monitor controllers have featured high-quality D-A converters for some time, and standalone D-A converters were released more recently. But until the new Convert-AD+, they’d not offered an A-D converter. So, having been impressed by every piece of Dangerous gear I’ve used to date, I was keen to see if their first A-D converter was worth the wait…
The front panel of the Convert-AD+ (I’ll call it the AD+) consists of a couple of different sections, and it’s all very intuitive. Leftmost is a button for changing the sample rate — pushing it switches between the usual sample rates from 44.1 up to 192 kHz. When the sample rate is stable, the Lock LED changes from red to green. When using the USB connection, the AD+ sets its internal clock according to the DAW settings that are detected — it can serve as a master clock for other equipment in this mode, but the clock rate is set by the DAW. This default mode can be defeated by holding the clock button for three seconds, after which the AD+ sample rate is only set by the front-panel button. Again, it can be used as a master clock for other connected equipment in this mode. The third option is to slave the AD+ to the external word-clock input. When you press the Word Clock button for five seconds the AD+ goes into master-clock mode, whereby the device ignores any incoming word clock signal.
Next is the Calibration section, and pressing the Select button sets the maximum input level (to +18, +20 or +22 dBu), making it easy to incorporate the converter in pretty much any existing setup.
Another convenience is that the Analog Input section offers the possibility of switching between two different stereo inputs. This simple, yet brilliant facility allows you to hook up, say, two instrument recording channels to the first stereo input, and analogue stereo-bus processing on the other. For instance, in my own studio, I have two vocal recording chains hooked up to the first input pair, and the stereo output from my analogue summing mixer feeding the second. But the dual input pairs would make it equally possible to, for example, change swiftly between two different analogue mastering chains.
As a young sound engineer, I received my education in the broadcast world, which makes me very picky when it comes to metering — I’ve used lots of high-end converters over the years, and the level metering on the AD+ is one of the most informative and fluent systems I’ve encountered. The level meter ranges from -80 to 0 dBFS and shows peak over average — displaying both RMS and peak information gives you a clear indication of the crest factor. Should you require even greater precision, the Zoom function sets the meters to display the input level only between -10 and 0 dBFS — perfect for mastering and checking exactly how loud the peaks really are. A Peak Hold function helps to keep track of loudest transients and the Over indicator goes from green to yellow when three consecutive samples have been clipped.
The right-most section controls two input transformers and a unique shelving EQ/compression circuitry that adds subtle harmonic distortion — all of which I will discuss in more detail below.
On the rear panel, in addition to the dual stereo XLR inputs there are plenty of digital options: dual AES3 outputs, ADAT and both optical and coaxial S/PDIF outputs, word-clock in and out, and a USB port. The last of these allows the AD+ to pass a signal to your DAW as one half of an audio interface — and Mac users could conceivably create an aggregate device that paired it with a Dangerous Convert-2 or Convert-8 D-A converter. During the test period, I used the USB connection to record analogue mixdowns at a high sample rate on a laptop, with good results.
The X-Former Insert consists of two Hammond input transformers, which have been designed deliberately to add some sonic flavour to the audio passing through. The Canadian Hammond company have been making transformers for a century, and according to Chris Muth, Dangerous Music’s chief design wizard, their transformers were chosen after auditioning all the usual brand-name suspects. Inserting the transformers tightens up the low end, with a gentle roll-off that starts at 100Hz and is down 0.5dB at 40Hz. Simultaneously, the removed bass energy is ‘folded up’ one octave due to added second harmonic distortion. The result is a slightly tighter low-end that translates better to small speakers. At the other end of the spectrum, there’s a gentle rise which starts at 3kHz and is up 1dB at 20kHz. At loud RMS levels, transformer core saturation kicks in and compresses the high-end a little bit.
Emphasis is a parallel analogue high-shelving EQ and compressor section, that also introduces second-harmonic distortion. The EQ starts boosting at 300Hz. When the knob is at 12 o’clock the boost is 1dB, and with the knob turned fully clockwise the boost is 2dB. The compressor, with a threshold (relative to the digital output) of about -14dBFS, lowers the gain of the signal before it’s blended back in with the dry signal. Both the transformers and the Emphasis circuitry are hard-bypassed when not in use.
On receiving the review unit and plumbing it in, I decided to commence my tests by re-recording an analogue mix that I’d recently completed. Normally, I use a Dangerous Convert-8 as my master clock, but I decided to let the AD+ perform this role, since both units share the same impressive low jitter tech specs. Pressing the Word Clock button for 5s put the converter into master clock mode, and after hooking up the analogue and digital cables, I was good to go.
Comparing the recorded result with the mix recorded through my other mastering-grade A-D converter, it was clear to me that the Convert-AD+ offered another level of depth and clarity. Not only did the mix sound slightly wider, but the whole stereo panorama also sounded somehow more coherent. Another thing that struck me was the upper mid-range clarity, which manifested itself as an opening up of the whole mix — just a little something extra. The mix already had a good-sounding mid-range depth, but I was pleasantly surprised to find it sounding even better defined when captured through the Convert AD+. In the context of A-D conversion, these differences are easily discernible — when you know a mix inside out it’s fairly easy to hear differences in the finer details of, say, reverb tails and effects. The icing on the cake for me was a beautiful low-end depth and definition, which sounded to me exactly like the all-analogue mix, as I’ll describe in more detail later.
While the Convert-AD+ performs an incredibly ‘pure’ conversion, it’s not purely about conversion — there’s that analogue processing too. And I became rather addicted to the sound of the input transformers and the Emphasis processing. I can best describe their combined contribution to the sound as ‘analogue polish’. They work in tandem to tighten the low end while adding mid-range warmth and ‘sparkle’. To help me put that in slightly less subjective words, I measured the harmonic distortion. As well as the EQ and compression, not only was a good dose of odd-order harmonics being added, but I could see that the distortion pattern is also frequency dependent — more second-harmonic distortion is added at low frequencies, and more third- and fifth-harmonic distortion at higher frequencies. The compression effect at high frequencies helps to control excessive peaks just a little bit too. All in all, I’d say that the analogue processing of the Convert-AD+ ranges from the very subtle to adding ‘a breath of fresh air’.
Less Is More…
Working with analogue processing and mixing, I found myself having to perform slightly fewer ‘tricks’ when recording mixes via the Convert-AD+, especially in the mid-range and higher frequencies — they just sounded coherent and smooth. Another area that became easier to massage was the low end: normally I face a fight to retain the depth and punch of the kick and bass instruments when recording, especially in a busy mix, but somehow, the low-end was captured from the lowest octave with such depth and clarity that I didn’t need to fight quite so much to make it work. To my ears, the low-end performance of the Convert AD+ was truly remarkable.
…But More Is OK!
It might strike you as silly to consciously design a high-end A-D converter to distort the signal, and personally I’ve never fancied doing it. Nevertheless, coaxing the Convert-AD+ into distortion shows how well it copes with excessive input levels. The analogue stages have amplitude and slew-rate capability well in excess of the A-D chip, which in turn has internal headroom above the digital output level. You can, then, push the input levels to clip the signal digitally without ever distorting the analogue front end or the ADC chip. Enabling the Clip Guard feature (the precise details of which Dangerous are remaining tight-lipped about) won’t prevent clipping, but it will prevent the meters in your DAW or digital recorder from indicating any overs — so, for example, a CD pressing plant won’t reject your master.
The Zoom function comes in handy for checking exactly how high the levels are, and the Over indicator turns from green to yellow when hitting 0dBFS. I suspect the yellow colour was chosen on purpose, rather than red, because it still sounds good hitting the converter with up to +4dB of excessive level. Naturally the results are subjective and program-dependent, but mastering engineers are going to want to try this converter for this purpose: typically, an A-D converter produces its most transparent result when the peak level is no hotter than -4dBFS, but who’s taking notes when it sounds like this?
It’s worth mentioning the internal digital clocking of the AD+, because it’s built around the JetPLL jitter-suppression technology used by quite a lot of professional audio-interface designers, but this has been further enhanced by the surrounding circuitry. The team at Dangerous Music have gone to great lengths to make it compete with the best; I’ve used a bunch of different word-clock generators in my own control room and I’m happy to state that the Convert AD+ is one of the best, if not the best I’ve used. Whether a digital master clock can improve the sound quality of external converters or not, where a master clock is needed it should be a really good one!
The published specs are impressive: the dynamic range is 118dB, the THD+N is less than 0.0011 percent at +4dBu, and the clock jitter 16ps (100Hz to 40 kHz). According to Dangerous President Bob Muller, the AD+ design process was the same as for all Dangerous gear, with the subjective perception of the sound made the first order of business. To this end, a few contenders for chips where chosen based on published data, then each chip was built into a very simple ‘black box’ with an analog input and an AES3 digital out. Then a series of blind listening tests were conducted, involving both the design team themselves and a select group of professional engineers, to determine the best-sounding chip. There was a strong consensus for the AKM AK5394A — it’s no wonder that this is so frequently used in high-quality audio interfaces and A-D converters!
The choice of converter chip, though, is only one piece of the design puzzle. The analogue front-end, power distribution and isolation, grounding and shielding, the clock and the isolation of the clock signal from the analogue and digital audio paths are all important factors that influence the end result. It’s here that Dangerous Music have gone the extra mile and this has, in my view, allowed them to create one of the best-sounding A-D converters on the market.
Some competitors choose to sample at a fixed high internal sample rate, and then apply sample-rate conversion to generate the desired sample rate output, but the Convert-AD+ doesn’t do this — because the Dangerous Music team just don’t believe this to be beneficial to the sound quality.
The Dangerous Music Convert-AD+ is a stellar-sounding, mastering-grade A-D converter. It’s super transparent, yet manages to be musical. The sound quality is undoubtedly amongst the best available, so this device is well suited for mastering engineers and music producers who demand the best possible sound quality. The input transformers and analogue processing are genuinely useful tools, and after some usage their combined effect on the music can become addictive. The other facilities, such as the exemplary clocking, thoughtful metering and switchable dual inputs, also make it a practical device in any setup.
Even with the impressively high-quality A-D converters already available, Dangerous Music have shown that it’s still possible to improve on both the design and sound quality. The Convert-AD+ will definitely not be leaving my control room any time soon!