Arcam irDAC-II D/A processor Measurements

Sidebar 3: Measurements

I measured the Arcam irDAC-II with my Audio Precision SYS2722 system (see the January 2008 As We See It"), using the Audio Precision's optical and electrical digital outputs, USB data sourced from my MacBook Pro running on battery power with Pure Music 3.0 playing WAV and AIFF test-tone files, and with the same files played on an iPhone 6S, an iPad2, and an HTC Android phone via Bluetooth. Apple's USB Prober utility identified the irDAC-II as "irDAC-II" from "ARCAM," and revealed that its USB port operated in the optimal isochronous asynchronous mode. Apple's AudioMIDI utility revealed that, via USB, the Arcam accepted 32-bit float and 24-bit integer data sampled at all rates from 44.1 to 384kHz. The optical input locked to datastreams with sample rates up to 96kHz, the coaxial S/PDIF inputs locked to streams of up to 192kHz-sampled data. Via Bluetooth, the Arcam was identified as "irDAC2 f93a."

The Arcam's maximum output level at 1kHz was 2.15V from both its variable and fixed line-level RCA jacks, 4.01V from its headphone jack, and all three outputs preserved absolute polarity (ie, were non-inverting). The output impedance from the fixed and variable outputs was a low 47 ohms from 20Hz to 20kHz, and the impedance from the headphone jack was a constant 1 ohm across the same range. The irDAC-II's impulse response with data sampled at 44.1kHz (fig.1) revealed the reconstruction filter to be a conventional FIR type, with time-symmetrical ringing.


Fig.1 Arcam irDAC-II, impulse response (one sample at 0dBFS, 44.1kHz sampling, 4ms time window).

The magenta and red traces in fig.2 show that this filter rolls off rapidly above the audioband, with the aliased product at 25kHz of a full-scale tone at 19.1kHz (cyan and blue traces) suppressed by >110dB. Fig.3 is a more conventional way of showing frequency response, in this instance taken with data sampled at 44.1, 96, 192, and 384kHz. In each case, the response falls sharply just below half the sample rate, and other than with 384kHz data, the channels are superbly well matched. At 384kHz, the right channel (green trace) rolls off a little earlier than the left (blue), reaching –3dB at 80kHz compared with 100kHz. Figs. 2 and 3 were taken from the fixed outputs; the responses were identical from the variable and headphone outputs.


Fig.2 Arcam irDAC-II, wideband spectrum of white noise at –4dBFS (left channel red, right magenta) and 19.1kHz tone at 0dBFS (left blue, right cyan), with data sampled at 44.1kHz (20dB/vertical div.).


Fig.3 Arcam irDAC-II, frequency response at –12dBFS into 100k ohms with data sampled at: 44.1kHz (left channel green, right gray), 96kHz (left cyan, right magenta), 192kHz (left blue, right red), 384kHz (left blue, right green) (1dB/vertical div.).

Channel separation (fig.4) was superb, at 125dB in both directions at 1kHz, and decreasing to a still-excellent 110dB at the top and bottom of the audioband, the former due to capacitive coupling somewhere in the circuit, the latter to the wall-wart supply's increasing impedance at low frequencies. The level of random background noise was very low, but some low-level spuriae were present at 60Hz and its odd-order harmonics (fig.5). Increasing the bit depth from 16 to 24 with a dithered 1kHz tone at –90dBFS dropped the noise floor by around 21dB (fig.6), suggesting that this inexpensive DAC offers close to 20-bit resolution, which is excellent. However, with 24-bit data (blue and red traces), the reduction in analog noise unmasks some distortion, the highest-level harmonic being the second. With an undithered 16-bit tone at –90.31dBFS (fig.7), the three DC voltage levels described by the data are very well defined, and other than 25µV DC offset in the right channel (red trace), the two channels match well. With 24-bit undithered data (fig.8), the Arcam output a well-formed sinewave despite the very low level of the tone.


Fig.4 Arcam irDAC-II, channel separation (5dB/vertical div.)


Fig.5 Arcam irDAC-II, spectrum with noise and spuriae of dithered 24-bit, 1kHz tone at 0dBFS (left channel blue, right red) (20dB/vertical div.).


Fig.6 Arcam irDAC-II, spectrum with noise and spuriae of dithered 1kHz tone at –90dBFS with: 16-bit data (left channel cyan, right magenta), 24-bit data (left blue, right red) (20dB/vertical div.).


Fig.7 Arcam irDAC-II, waveform of undithered 1kHz sinewave at –90.31dBFS, 16-bit TosLink data (left channel blue, right red).


Fig.8 Arcam irDAC-II, waveform of undithered 1kHz sinewave at –90.31dBFS, 24-bit TosLink data (left channel blue, right red).

Harmonic distortion at high signal levels was very low, even into 600 ohms (fig.9), with the third harmonic the highest in level from the line outputs at just –111dB (0.0003%). From the headphone outputs, the second harmonic was the highest in level, at the same –111dB. All the previous tests were taken with S/PDIF or USB data; as with Bluetooth-sourced data, the performance will greatly depend on the code used, whether aptX (Android phones and my MacBook Pro) or SBC (iPhones and iPads). I examined the behavior of these codecs in the measurements that accompanied our review of Arcam's rBlink. Basically, the superior-sounding aptX trades off low-level resolution in favor of preserving a random noise floor, whereas AAC seems to try to preserve resolution at the expense of noise-floor modulation and the introduction of enharmonic spuriae. However, even aptX introduces noise modulation, as can be seen in fig.10, which plots the spectrum of the Arcam's output as it decodes aptX-encoded Bluetooth data representing a 1kHz tone at 0dBFS (blue and red traces) and at –20dBFS (green and gray). The level of the random noise floor is related to the signal level. Incidentally, I created this graph using my MacBook Pro as the Bluetooth source; the only Android phone available to me produced around 2% of odd-order distortion with full-scale tones, even with its volume control set to –12dB.


Fig.9 Arcam irDAC-II, spectrum of 50Hz sinewave, DC–1kHz, at 0dBFS into 600 ohms (left channel blue, right red; linear frequency scale).


Fig.10 Arcam irDAC-II, spectrum of 1kHz sinewave, DC–10kHz, at 0dBFS (left channel blue, right red) and at –20dBFS (left green, right gray), both sourced from MacBook Pro via Bluetooth (linear frequency scale).

Intermodulation distortion was extremely low (fig.11), as was the irDAC-II's rejection of word-clock jitter via its S/PDIF and USB inputs (fig.12), with the odd-order harmonics of the LSB-level, low-frequency squarewave at the correct level (green line), and no other sidebands visible. With 24-bit J-Test data (fig.13), there are no sidebands present but some low-level spurious tones can be seen. Overall, its measurements suggests that the inexpensive irDAC-II is a conventional but well-engineered D/A processor.—John Atkinson


Fig.11 Arcam irDAC-II, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 0dBFS into 600 ohms, 44.1kHz data (left channel blue, right red; linear frequency scale).


Fig.12 Arcam irDAC-II, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz: 16-bit TosLink data (left channel blue, right red). Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz.


Fig.13 Arcam irDAC-II, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz: 24-bit TosLink data (left channel blue, right red). Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz.

US distributor: The Sound Organisation
1009 Oakmead Dr.
Arlington, TX 76011
(972) 234-0182

tonykaz's picture

Who else should I ask?, am I asking the right person?

This Lamm Reference RIAA preamp for instance. Is it Class A Recommended? or is the Manufacturer claiming it to be well above Class A?

Seems like plenty of outfits are claiming their stuff to be Reference Class.

So, should we now expect there to be : Reference Class, Class A, Class B, Class C, etc?

Besides, is there anything in the Vinyl chain that could be Reference?, like a Clock traceable to WWV's HP Atomic Clock.

Maybe "Reference" is a "Tuning Fork".

Of course 16/44.1 Redbook would have to be a Reference, wouldn't it? and now 24/44.1 & 24/48 are useful References, aren't they?

How can a Vinyl Record be Reference, there are virtually no standards (what so ever) in the Vinyl industry or in Playback gear.

Un-less, what Chad Kassem says is true: most of the Vinyl being made is from the Digital Master ( which is of a Reference Standard ).

Confused Tony in Michigan

John Atkinson's picture
tonykaz wrote:
Who else should I ask?, am I asking the right person?

Right person but possibly the wrong thread, as this is the Arcam DAC review.

tonykaz wrote:
This Lamm Reference RIAA preamp for instance. Is it Class A Recommended? or is the Manufacturer claiming it to be well above Class A?

When you see the word "Reference" in a Stereophile review, it means that the word is part of the product's formal name, nothing more.

John Atkinson
Editor, Stereophile

tonykaz's picture

it means nothing more, it's just a name, an arbitrary selection by the Company, no reference to any Established Reference.

I suppose, in short, it's BS.

Why do we have these ><)))))'> smells in Audiophile marketing?

I suppose this is why we need our JA & Tyll

Tony in Michigan

dalethorn's picture

"Besides, is there anything in the Vinyl chain that could be Reference?, like a Clock traceable to WWV's HP Atomic Clock."

Last time I checked, the Atomic Clock by HP will give very accurate results, but is not regulated for jitter. That's the inherent problem in converting Cesium streaming to other formats.

tonykaz's picture

You always seem smarter than me.

How'm I supposed to know about Cesium jitters?

I live in Fly-over country,

The god concept alone gives me the jitters, now I gotta worry about my clocks giving jitters.

Maybe I should return to my first love : Vodka

Tony in Michigan

Glotz's picture

Fo' sure. Great review and references, as I own many of the same Gabriel recordings referenced in the review. I really wish it had MQA.. but I am patient.

Might I make recommendation? Try Herbie's Audio Labs' products sandwiched between the rack shelves of your Target TT-5. I have, and for the absolute pittance in price, sooooo worth it. (Tens of dollars for the entire rack.. not hundreds.)

Platinum-cured silicone is really an amazing material for audio. Nothing like Sorbothane or other squishy products similar to that material. It actually 'de-couples' gear very well, and at a 1/100th of the cost of ball-bearing feet, etc. Their Grungebuster platter mat competes with the best mats out there, and is extremely reasonable in price as well. Any one using an acrylic platter should look into this product (if an aluminum platter is not financially feasible). I reeeeally want to see a turntable company use the products as a 'sandwich' filler some day.

Their website is 'meh', but it's about the products. (I have no relationship whatsoever with their company... just a customer.)

mrkaic's picture

...machine reviewed here. I was under the impression that this magazine has become a newsletter for the scientifically uneducated ruling class.

A few more reviews like this one and I will say "Bravo!"

tonykaz's picture

Good one, Mr. mrkaic !

mind if I borrow it, from time to time?

Tony in Michigan

ps. I might simplify it by say'n : Uneducated Ruling Class or Inherited Ruling Class. Either which way, I bow to your wisdoms.

mrkaic's picture

... is probably not a very common one and has nothing to do with politics and more with my perception of social power. For example, I think than rich anti vaxxers, clueless movie and music stars who pontificate about every moral panic they can think of (without having any scientific qualifications, of course), professional athletes, pundits and talking heads who talk about just any issue without ever doing any serious analytical work etc. are the true ruling class of today.

The Onion nailed this years ago:

But feel free to borrow the phrase, no problem.

tonykaz's picture


I had to look up anti-vaxxers. ( my chiropractor is an anti-vaxxer, I'm not! ).

Tony in Michigan

Anon2's picture

I am a proud Arcam fan and loyal owner of the brand's products.

I am encouraged by the fact that the writer of this article saw fit to hook up this next generation Arcam DAC directly to his power amp. I am seeing more DAC/headphone Amps that allow a more budget-constrained consumer a quicker path to separates.

Keep making the hints. We'll keep taking them.

I have been an enthusiastic fan of Arcam DACs. I plan on continuing to purchase Arcam DACs. I do regret that they elected to discontinue the superb performance and portability of the r-Pac. The r-Pac has become "my stereo" (along with headphones) for most of the week.

There is one thing that I hope Arcam addresses. Perhaps they have addressed this issue. On the rDac, including two that I have owned, there is this strange clicking noise, and blanking out of the sound, when these devices are on certain outlets. This occurs through power strips where other electronics (TVs and audio gear) show no strange or similarly intermittent performance. A perusal of web postings shows that I am not the only reporter of this apparent defect of the rDac.

My dealer had to replace an rDac that had this problem. The replacement exhibits the behavior intermittently. I have learned to deal with it because, besides this problem, the rDac is a category-leading device.

I hope Arcam has fixed this. Perhaps we can get some Stereophile or manufacturer comments to this effect in this comments stream.

Besides this problem with the rDac, which I hope has not happened with successor models, Arcam is a superb brand offering great performance for the money (though I'm still to be sold on Class-G amplification).

wozwoz's picture

I cannot think of anything more inappropriate or off-putting in a high-end hi-fi product than the inclusion of wireless or Bluetooth. The very last thing I want in my personal musical sanctuary is to have my brain or body made the subject of unnecessary radiation that is known to damage DNA in scientific tests. And while Bluetooth is generally a low-strength power source, if it is close enough to your body, it has an effect, just like mobile phones or wi-fi routers. I don't use a Bluetooth mouse or keyboard for the same reason - they give me headaches / buzzing which I frankly don't need. Aside from the health reasons, why you would want your music compressed and distorted by low-res Bluetooth compression in a high-end hi-fi product is simply beyond belief, and serves to discredit both this product and its manufacturer.

labjr's picture

"Carpenters' Singles 1969–1981 (DSD64 file, A&M/Analogue Productions)"

Is there a version of this album that was an "Analog Productions" project and not just a DSD file that Acoustic Sounds is selling?

John Atkinson's picture
labjr wrote:
Is there a version of this album that was an "Analog Productions" project and not just a DSD file that Acoustic Sounds is selling?

No, it is the DSD version that Acoustic Sounds sells.

John Atkinson
Editor, Stereophile