Arcam FMJ D33 D/A processor Measurements

Sidebar 3: Measurements

I examined the Arcam FMJ D33's electrical performance with Stereophile's loan sample of the top-of-the-line Audio Precision SYS2722 system (see www.ap.com and the January 2008 "As We See It"); for some tests, I also used my vintage Audio Precision System One Dual Domain. The maximum output level at 1kHz was 4.732V from the balanced XLR jacks, 2.184V from the single-ended RCAs, the latter 0.76dB higher than the CD standard's 2V. Both pairs of outputs preserved absolute polarity (ie, were non-inverting). The XLRs are wired with pin 2 hot. The output impedance was a low 47 ohms from the RCA jacks, 142 ohms from the XLRs.

The D33's TosLink input locked to data with sample rates up to 96kHz, the coaxial S/PDIF input up to 192kHz, though the AES/EBU input wouldn't lock to the SYS2722's AES/EBU output. The Apple USB Prober utility revealed the USB1.1 input port as "ARCAM USB Audio 1.0," operating in isochronous asynchronous mode and handling 24-bit data with sample rates up to 96kHz, including 88.2kHz. The USB2.0 input port was identified as "ARCAM USB Audio 2.0" using "ARCAM DFU" firmware, and again operating in isochronous asynchronous mode. This input successfully operated with 24-bit data and sample rates up to 192kHz, including 176.4kHz.

Fig.1 shows the D33's impulse response with 44.1kHz data (one sample at 0dBFS) and with the Burr-Brown DAC chip's default filter engaged. The symmetrical ringing either side of the pulse reveals this filter to be a conventional linear-phase type. Switching to Arcam's Filter 1 gave the impulse response shown in fig.2. The ringing now occurs after the pulse, meaning that the filter is a minimum-phase type. By contrast, Filter 2 has a single cycle of damped ringing (fig.3). The frequency response with the Burr-Brown filter (fig.4) is conventional, with a sharp rolloff just below the sampling frequency. Not only is Filter 1 a minimum-phase type, its frequency response (fig.5) confirms that it is an "apodizing" filter; ie, it has a null at half the baseband sample rate, something that correlates with improved sound quality. With 192kHz data (green and gray traces), the response follows the smooth rolloff seen with lower sample rates, reaching –3dB at 60kHz. As suspected from its impulse response, Filter 2 is a slow-rolloff type that optimizes the time-domain performance at the expense of allowing some aliasing energy to leak into the audioband (fig.6).

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Fig.1 Arcam FMJ D33, impulse response with default filter (4ms time window).

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Fig.2 Arcam FMJ D33, impulse response with Filter 1 (4ms time window).

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Fig.3 Arcam FMJ D33, impulse response with Filter 2 (4ms time window).

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Fig.4 Arcam FMJ D33, Burr-Brown Filter, 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) (0.25dB/vertical div.).

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Fig.5 Arcam FMJ D33, Filter 1, 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) (0.25dB/vertical div.).

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Fig.6 Arcam FMJ D33, Filter 2, 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) (0.25dB/vertical div.).

The 0.2dB channel imbalance in these response graphs is larger than I would have expected. Channel separation, however, was excellent, at >125dB below 1kHz, and still 112dB at the top of the audioband. Other than some supply-related spuriae at 60Hz and its third and fifth harmonics, these all lying at or below –130dBFS (0.00003%), the D33 had a superbly low noise floor (fig.7). Increasing the bit depth from 16 to 24 with a dithered 1kHz tone at –90dBFS therefore dropped the noise by >14dB (figs.8, and 9), implying resolution of at least 18 bits. These graphs were taken via the coaxial S/PDIF input. The USB ports gave identical performance, revealing that they do indeed operate without truncating the 24-bit data. (See the "Measurements" sidebar of the review of AVM's Evolution C9 elsewhere in this issue for what happens with word-length truncation.) The peaks in these graphs just kiss the –90dBFS line, implying good low-level linearity, which, in conjunction with the low noise, allowed the D33 to reproduce a good facsimile of a sinewave with undithered 24-bit data at –90.31dBFS (fig.10). With undithered 16-bit data (fig.11), the Arcam DAC clearly distinguished the three DC voltage levels described by these data.

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Fig.7 Arcam FMJ D33, spectrum with noise and spuriae of 1kHz tone at 0dBFS with 16-bit data (left channel cyan, right magenta) and 24-bit data (left blue, right red) (linear frequency scale).

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Fig.8 Arcam FMJ D33, 1/3-octave spectrum with noise and spuriae of dithered 1kHz tone at –90dBFS with 16-bit data (top) and 24-bit data (bottom) (right channel dashed).

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Fig.9 Arcam FMJ D33, with noise and spuriae of dithered 1kHz tone at –90dBFS with 16-bit data (left channel cyan, right magenta) and 24-bit data (left blue, right red) (linear frequency scale).

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Fig.10 Arcam FMJ D33, waveform of undithered 1kHz sinewave at –90.31dBFS, 24-bit data (left channel blue, right red).

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Fig.11 Arcam FMJ D33, waveform of undithered 1kHz sinewave at –90.31dBFS, 16-bit data (left channel blue, right red).

The D33 gave low levels of harmonic distortion, even with a punishing 600 ohm load (fig.12). The second and third harmonics are the only harmonics visible in this graph, which would be subjectively innocuous even if they lay higher than –80dB (0.01%). Tested for high-frequency intermodulation distortion with an equal mix of 19 and 20kHz tones and the D33 set to Filter 1, the second-order difference product lay at a very low –106dB (0.0005%) (fig.13), with the images of the primary tones at 25.1 and 24.1kHz well suppressed at below –90dB (0.003%). With the slow-rolloff Filter 2, however (fig.14), though intermodulation remains very low, the ultrasonic images are only 10dB lower in level than the primary tones, and some low-level aliasing products are now visible in the audioband. The steep rolloff of the Burr-Brown filter gave the lowest intermodulation and image suppression (fig.15).

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Fig.12 Arcam FMJ D33, spectrum of 50Hz sinewave, DC–1kHz, at 0dBFS into 600 ohms (left channel blue, right red; linear frequency scale).

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Fig.13 Arcam FMJ D33, Filter 1, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 0dBFS into 100k ohms (left channel blue, right red; linear frequency scale).

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Fig.14 Arcam FMJ D33, Filter 2, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 0dBFS into 100k ohms (left channel blue, right red; linear frequency scale).

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Fig.15 Arcam FMJ D33, Burr-Brown Filter, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 0dBFS into 100k ohms (left channel blue, right red; linear frequency scale).

The Arcam demonstrated excellent jitter rejection on its S/PDIF inputs. Operating in the preferred asynchronous mode, the D33's USB inputs were equally good, with a well-defined central peak representing the tone at one-quarter the sample rate and a clean noise floor free from jitter-related sidebands (fig.16).

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Fig.16 Arcam FMJ D33, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz: 24-bit data via USB from MacBook Pro (left channel blue, right red). Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz.

Its measured performance indicates that the Arcam FMJ D33 is as well-engineered a product as I have come to expect from Arcam.—John Atkinson

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Arcam
US distributor: American Audio & Video
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Southaven, MS 38672
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COMMENTS
Robby's picture

While the measurements look alright, can this product actually produce enjoyable music? It's called Faithful Musical Joy after all...

This device is full of way too many opamps with vanishingly low THD+N spec sheets (high negative feedback, class AB output stages anyone?) and even the reviewer has found the sound 'harsh' and 'in your face' in some cases! Even the balanced outputs are created by an opamp from a single-ended signal... is this where high-end is going?

For $3200?

How can this be 'recommended' over the dozen of other less expensive, better engineered and cheaper alternatives?

Congratulations to Arcam for being able to demonstrate the integration of so many different TI chips in a single device, they probably got a good deal on that order.

John Atkinson's picture

Quote:
This device is full of way too many opamps with vanishingly low THD+N spec sheets (high negative feedback, class AB output stages anyone?). . .

Philosophical objections like this aside, what did you think of the Arcam FMJ FD33's sound?

John Atkinson

Editor, Stereophile

Robby's picture

Generally speaking I haven't enjoyed the DACs I've recently listened to that use TI digital to analog converter chips. And by listen I mean, spent time with them in my own system. I didn't get to hear Arcam's DAC seriously hence why I appreciate reading what *you* think about it.

Fundamentally I don't believe it's a question of what the readers think about it, but rather what you guys think about that product since you have the opportunity to listen to way more DACs than us mere mortals.

What you write has the potential to influence people's decisions to a certain extent and to me 'recommending' something means that in the context of that product's price range, features, etc... you would yourself select it instead of a competitor's offering. (at least that's how I interpret the summary).

Would you pick the Arcam as a DAC for yourself if you were shopping for a DAC in that price range?

John Atkinson's picture

Robby wrote:
Would you pick the Arcam as a DAC for yourself if you were shopping for a DAC in that price range?

Yes, because its F1 filter is one of the best-sounding reconstruction filters I have tried.

John Atkinson

Editor, Stereophile

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