MEASUREMENTS: RME ADI-2 Pro FS R Black Edition as ADC.

About a month ago, I posted this preview of the RME ADI-2 Pro FS R Black Edition AD/DA converter. It has been a wonderful month of simply listening to this device without a care around performing measurements. For listening, I have it set up as per the image in my sound room with the Raspberry Pi "Touch" running RoPieee previously discussed.

So far, from a subjective perspective, it has been a joy to listen to music with this machine.

Alas, as a "more objective" audiophile, it came time to have a look at the performance for this device to check if I'm missing any significant limitations. Over the years, I've discussed limitations to human hearing as well as the idea that many of our audio electronics these days have surpassed human auditory perception such that while measurements of DACs or amplifiers can show limitations, often these are beyond the resolution thresholds of human hearing/perception. Remember that while not all measurable anomalies need to be chased after when the goal is simply to be able to enjoy music, technical "ideals" are useful for devices one may want to use as a "reference".

So to start, today let's just focus on the ADC side of this RME device. Remember that the RME ADI-2 Pro FS R Black Edition (again, let me just call it the "FS R BE" for short) is an evolutionary step from the ADI-2 Pro FS ("Pro FS") that I started using 2 years ago. Consider this article as building on some of what we already know about the Pro FS as an ADC from 2018 with requisite repeated tests comparing the two machines and using today's software.

PREVIEW: RME ADI-2 Pro FS R Black Edition AD/DA Converter

Look what showed up at my door (finally!) the other day. This is the latest hardware update to the RME ADI-2 Pro line of converters, the RME ADI-2 Pro FS R "Black Edition" - quite the mouthful! Let's just use "FS R BE" for the rest of this article for short in reference to the name.

Currently, the street price is around US$2,000.

Back in mid January, RME debuted this latest iteration of the ADI-2 Pro at NAMM 2020. Since 2018, I have been in contact with Matthias Carstens (co-founder of RME) off and on about the ADI-2 Pro FS that I have been using for measurements on this blog. Shortly after NAMM, I contacted Matthias about getting an upgrade as I could use two of these ADI-2 Pro devices - one for the soundroom and another for my test bench - when the company starts shipping these.

MEASUREMENTS: RME ADI-2 Pro FS as DAC (Part II - frequency response, noise, distortion and jitter)

As we saw previously, the RME ADI-2 Pro FS is based on the AKM AK4490 DAC chip and provides a good assortment of features like filter settings. We've seen that the headphone output amplifier provides plenty of power and the beginnings of what looks like a highly accurate DAC; consistent with my subjective opinion.

Time for part 2 of the objective evaluation today as we continue to explore the DAC output quality.

MEASUREMENTS: RME ADI-2 Pro FS as DAC (Part I - output levels & digital filter settings)

After having explored a couple weeks back the ADC capabilities of the RME ADI-2 Pro FS, for this installment, let's start with evaluating the DAC output quality of the device and in the process examine the objective fidelity with audio playback.

Remember, with that previous article, I had already discussed my subjective opinions based on listening sessions. My opinion has not changed in the last number of weeks as I'm still very much enjoying the sound I hear hooked up to my main system. Subjectively, the output sounds very clean, has a neutral tonality and low noise level very much like the Oppo UDP-205 and other high quality DACs. As usual, it will be interesting to compare measured results among the different devices I put through the test bench.

But before we do that... Let's start with the basics and some of the "microscopic" measurements I usually begin with - things like output levels, filter settings, etc...

MEASUREMENTS: RME ADI-2 Pro FS ADC performance and as measurement hardware.

I discussed the features and some listening impressions of the RME ADI-2 Pro FS ADC/DAC a couple weeks ago. As I noted at that time, my main aim in owning this device is for the purpose of using it as an ADC for measurements here on the blog going forward.

For the purpose of measurements, we want a tool that can allow us to obtain reproducible results and good accuracy. Over the years, I've achieved reproducible results with consistently minimal inter-test variation by standardizing the way I run most measurements with the digital sources, cables, standard procedures, and types of tests I run. What I want is better accuracy - an ADC that has lower noise floor for improved resolution, doesn't add as much of its own distortions, have higher timing accuracy (eg. for jitter tests), and perhaps more features to expand the measurement quality (eg. higher sample rate to capture impulse responses more accurately, and can handle wider input levels for the range of devices tested).

Given that this is the priority, instead of measurements of DAC performance first, let's get straight to describing the characteristics of and using the ADI-2 Pro as a measurement tool which means we'll need to get a taste of how well the analogue-to-digital capability performs. Let's compare the results I'm getting from the RME to my previous measurement ADC device over the last couple years, the Focusrite Forte for a sense of the changes in resolution I can expect from the new upgrade.

PREVIEW: RME ADI-2 Pro FS AD/DA Converter

I. Prologue

For those who have followed along on the blog, you may recall that this blog started with some arguments I had with folks on an audiophile forum around the audibility of high bitrate MP3. Back in those days (err... late 2012), there were all kinds of claims made by quite a few hobbyists that they could "easily" differentiate lossless FLAC from 320kbps MP3. I'm sure there are still many in the audiophile forums who hold this view although I think things have softened about the magnitude of differentiability (I think this shift has changed with high-res audio as well).

That disagreement was enough to push me to put out a blind test, to start looking into what I could do to help further my own understanding and awareness around audio hardware. The articles on this blog basically have been the culmination of that pursuit in hopes that the ideas and tests have been useful for others also on this journey looking for some clarity, typically found with more objective analysis.

Objective testing requires disciplined procedures and tools. Methods to reduce variables so that we can have reasonable "apples-to-apples" comparisons and reduce or eliminate psychological biases when we make decisions and search out facts beyond opinions colored by idiosyncratic preferences. Whether it's using an ABX tool, asking a partner/spouse/family/friend/neighbor to change something without our knowledge when listening, or measurement devices - letting the tool demonstrate changes - I believe we can find answers to uncertainties or prove claims. I personally believe objective testing is not only something "nice to have" with reviews, but an essential part of developing insight into the devices being tested and our own perceptual and cognitive limitations.

That's a long intro which brings us to today's preview of a new tool. :-)

When it comes to using an ADC for measurements, over the years, I've gradually upgraded starting with my old Creative E-MU 0404USB from 2012, to the Focusrite Forte in 2016, and now, let's start with a look and listen to the RME ADI-2 Pro FS ADC/DAC. The aim has been that each step brings with it more accuracy for the measurements and this third iteration of the measurement hardware should bring with it opportunities to explore further and continue the process of finding clarity in a hobby that for too long IMO has been filled just with mere opinions - or even worse perpetuation of myths. (Remember, nothing wrong with opinions... But let's make sure it's grounded in objectivity!)

MEASUREMENTS: Focusrite Forte USB Audio Interface (ADC & DAC) + Summer Musings

Product shot from here.

A few weeks back, I mentioned that I grabbed one of these Focusrite Forte USB2 audio interface units for some home recording projects I wanted to do. Beyond using it as a measurement device, my old Creative E-MU 0404USB was being used for some of these recordings and I figured it was time to upgrade to something new since a couple of the analogue pots were getting a little scratchy and I figured an all-digital device like this would allow me to more accurately adjust the volume on the microphone pre-amps (indeed it has worked out very well!).

A size comparison.

MEASUREMENTS: Tascam UH-7000 USB Interface (Part II: As an ADC)

TEAC & Tascam combo with size differential. The E-MU 0404USB in the background to the left.

Alright, it's time to spend some time looking at using the Tascam UH-7000 as an analogue-to-digital converter. Remember in the first instalment, I showed that this device is already a very good DAC. This time around, I wanted to see whether this device did the job well as an ADC; my main desire being to use it for vinyl needle drops and to see if it can be used as a good measuring device in comparison to the Creative E-MU 0404USB I've been using for the last couple years (which I bought mainly as a DAC back in 2009).

MEASUREMENTS: E-MU 0404USB.

Since late 2012, I upgraded my computer workstation's DAC to the ASUS XONAR Essence One and this left my E-MU 0404USB free to be used as a dedicated ADC and measurement device.

For ease of use, I decided to "standardize" on the RightMark Audio Analyzer suite of measurements for these USB0404 measurements. At this time, the newest version is 6.2.5, available free from the website. In time, I might upgrade to the PRO version. What I can say so far is that RMAA is remarkably consistent with good inter-test reliability so long as one has the technique figured out with one's equipment. It's very easy to get things wrong during calibration for example. As usual, there are the caveats to keep in mind and the results I get here may not be comparable with others (good writeup here: http://nwavguy.blogspot.ca/2011/02/r...yzer-rmaa.html).

One nice feature about external DAC/ADC's like this one is the fact that it has LED's to indicate if signal is clipping. I've found this invaluable in measurements since it allows me to make sure I'm maximizing the measurable dynamic range.

To get a sense of what the E-MU 0404USB is capable of, here are a few numbers in RCA loopback mode - it looks like the 0404USB is not bad as a DAC itself! Internal DAC chip AKM AK4396 (same as Transporter).

Setup: AMD Phenom X4 Win 8 laptop on battery <---> USB2 <---> E-MU 0404USB (RCA loopback)
0404USB Driver: 1.40.00 Beta, L6.1.30.07 firmware.
USB cable used: generic high quality (<$20)
RCA cable: simple Radio Shack headphone phono to stereo RCA cable. As you can see in the image above, I have some generic RCA-to-XLR converters as well to plug into the analogue inputs up front.

Summary compared with Logitech Transporter (more detailed measurements of this device in a future blog post):


Notice that the Transporter measures better here but it is using XLR cables. If I had some balanced TSR to XLR's for the E-MU, I suspect the it would be even better.

Nice and flat frequency response at 24/96:

Here's the THD graph (24/96 again):

The jitter is really good for the E-MU also (it uses an asynchronous USB2 interface). This was done with the Dunn J-Test at 24/48 playing and analyzed with WaveSpectra 1.40E running a 131,072 point Blackman-Harris FFT. Note that I have seen various comments made in the forums that the 0404USB has bad jitter issues - well, I don't see it, in fact if I were to estimate, we're looking at <250ps using both the DAC and ADC in this case:


With digital silence playing, here's what the noise floor looks like:

A few spikes noted, the tallest about -135dB down.

Noise floor zoomed into 0-100Hz range - notice essentially no 60Hz pollution:


For such an inexpensive unit, I'm impressed! In the days ahead, I'll update this blog with the other DAC's and devices tested... I certainly do not claim that the 0404USB is near as good as dedicated measurement gear like the AP devices used by Stereophile. However, for the at home hobbyist, I suspect these kinds of tests will do nicely to help differentiate what's reasonably good from the bad.

From a subjective perspective, I've enjoyed using the 0404USB as my main DAC for about 3 years. The sound is precise and clean. Some would call it "analytical" but I honestly have no idea what that's supposed to mean since that sounds like a good thing to me :-). Basically, an honest portrayal of the digital audio with a good flat frequency response.

I do have a few gripes:
1. It's discontinued and the drivers were never great.  As noted above, I'm using the latest "beta" driver which is at least a couple years old. At least it's still compatible with Windows 8! On occasion, if I used the ASIO driver, it would mess up Windows mixer and I'd need to reset the sampling playback rate.

2. The headphone out is weak. It's fine with efficient headphones but my AKG Q701's were too much for the headphone amp.

3. Volume pot's got a bit noisy over the years.