Grimm Audio MU1 music streamer Measurements

Sidebar 3: Measurements

I examined the amount of timing uncertainty—jitter—in the Grimm Audio MU1's AES/EBU output using my Audio Precision SYS2722 system's digital oscilloscope function. I overlaid successive snapshots of the MU1's AES/EBU output, taken over a 60-second time window, to show what's called an "eye pattern." To make things as difficult as possible for the MU1, the AES/EBU link was a 45' length of Canare 110 ohm balanced interconnect and the data represented the 24-bit Miller-Dunn J-Test signal sampled at 44.1kHz. With an ideal transmission system, all the pulse transitions in the datastream will overlay one another to produce an image of a wide-open "eye," with just one trace visible.

Fig.1 was taken with the original 44.1kHz data (no upsampling) plotted over one "unit cycle." The eye is wide open, with no blurring of the leading and trailing edges. The average jitter level, assessed with a 50Hz–100kHz bandwidth, was 291.3 picoseconds (ps). Figs.2 and 3 show the eye pattern with 2× and 4× upsampling to 88.2kHz and 176.4kHz, respectively. Other than the reduction in the width of the eye, there is still no blurring, though the very long interconnect lengthens the waveform's risetimes. The average jitter levels were 291.3ps at 88.2kHz and 340.3ps at 176.4kHz. While these jitter figures are higher than Grimm's specified <0.6ps, the latter refers to the jitter on the MU1's master clock, while my measurements refer to the data-related jitter due to the transmission of the J-Test signal via the very long AES/EBU cable. For comparison, playing data representing a 24-bit 1kHz tone sampled at 88.2kHz reduced the jitter to 192ps, while the optical output of the Astell&Kern portable player I used for some of my auditioning had 1119ps of jitter.

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Fig.1 Grimm MU1, eye pattern of AES/EBU data output carrying 24-bit, 44.1kHz J-Test data, no upsampling (±2V vertical scale, 175ns horizontal scale).

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Fig.2 Grimm MU1, eye pattern of AES/EBU data output carrying 24-bit, 44.1kHz J-Test data upsampled to 88.2kHz (±2V vertical scale, 175ns horizontal scale).

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Fig.3 Grimm MU1, eye pattern of AES/EBU data output carrying 24-bit, 44.1kHz J-Test data upsampled to 176.4kHz (±2V vertical scale, 175ns horizontal scale).

Analyzed in the digital domain, with no D/A conversion, the Grimm MU1's "Pure Nyquist" filter used for the upsampling appears to be a very long linear-phase type, with a lot of pre- and postringing on either side of the single full-scale sample (fig.4).

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Fig.4 Grimm MU1, digital-domain impulse response sampled at 44.1kHz, upsampled to 176.4kHz.

While the upsampling doesn't add any data above the original sample rate's Nyquist frequency—22.05kHz with 44.1kHz data—this filter has an extremely steep rolloff, reaching full stop-band attenuation at 22.05kHz (fig.5). For reference, the red and blue traces in fig.6 show the ultrasonic rolloff of the MBL N31's Fast reconstruction filter with the same signal and plotted over the same octave between 15kHz and 30kHz. (Note that this spectrum was taken from the MBL's analog outputs; the ultrasonic noise floor is therefore higher than it is in fig.5, which shows the spectrum of the data analyzed in the digital domain.) The green and gray traces show the rolloff with the N31's Min (minimum phase) filter. The paradox is that I preferred this filter's slow rolloff with 44.1kHz data compared with that of the MBL's Fast filter, yet I preferred the upsampled MU1's ultrafast rolloff shown in fig.5. 221Grimmfig5

Fig.5 Grimm MU1, digital-domain spectrum, 15kHz–30kHz, of 24-bit white noise sampled at 44.1kHz at –4dBFS and upsampled to 88.2kHz (left channel blue, right red; linear frequency scale, 20dB/vertical div.).

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Fig.6 MBL N31, analog-domain spectrum, 15kHz–30kHz, of 24-bit white noise sampled at 44.1kHz at –4dBFS with Fast filter (left channel blue, right red) and Min filter (left channel green, right gray; linear frequency scale, 20dB/vertical div.).

Finally, I examined the question of whether the MU1's digital-domain volume control lost resolution at settings below the maximum. Fig.7 shows the FFT-derived spectrum of data representing a 24-bit 1kHz tone as transmitted via AES/EBU with the volume control set to “0” (red), "–10" (blue), and "–20" (green). Reducing the volume by 10dB lowers the 24-bit noise floor by 10dB; reducing the volume by 20dB lowers the noise floor by 20dB. The Grimm MU1's volume control does indeed preserve resolution at lower settings.—John Atkinson

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Fig.7 Grimm MU1, digital-domain spectrum, 1Hz–5kHz, of 24-bit. 1kHz tone with volume control set to "0" (red), "–10" (blue), and "–20" (green) (20dB/vertical div.).

COMPANY INFO
Grimm Audio BV
Eindhoven
The Netherlands
(+31) 40 213 1562
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COMMENTS
dumbordumber's picture

A lot appears to have been spent on the casing of this item, particularly the top. However, the interior is a very different kettle of fish. It looks lashed together. Standard length cables, folded and cable-tied. The DC, digital and signal cables are all unprotected from RF and EMI. The casing interior has no damping of any sort, no special layout, or suspension of circuit boards, just old-school steel pillars. In fact the interior of this device largely looks like a computer that has been assembled from fairly standard off-the-shelf components by your local computer shop. I have no doubt that it sounds good if those components are well matched and well chosen, and if the power supplies are decent. But so do many home built computers costing far less. This really is a lamb in wolf's clothing.
If I had bought this device and not known what was inside, I would have been expecting, for the price, something akin to Naim's layout and military wiring. If I had opened it up and found what lay inside, my face would have looked...well, Grim.

Jack L's picture

Hi

I concur with yr candid comment: "grim" - uninviting !

It should sound superb as reflected from its lofty price. Yet its so-so internal fabrication looks like some "of-the-shelf" stuff built by a neighbourhood computer repair shop. Hopefully it's actually "a lamb in wolf's clothing" !!

I said so from my recent experience. Just 2 weeks back I got a very basic DAC of an audio unknown brand-name in New York for an unbelievable very dirt crappie price from Amazon.

I acquired it sorta for 'fun' as digital is always my back burner music source vs vinyl classical music I addicted to.

It got basic Toslink & coaxial input & unbalanced RCA audio O/P & earphone jack featuring no-joke 24bit 192KHz sampling rate with 3 year free warranty.

Beyond my expectation for such crappie price, this New Yorker sounds pretty decent with its coaxial input & audio O/P hooked up to my design/built phono-linestage with straight-line bypass mode ON.

This Little David from New York makes ALL my CDs & DVDs sound so much better than before ! WoW. So pleasantly surprised !!

Play digital smart, dear consumers !

Listening is believing

Jack L

Jack L's picture

Hi

Despite its very dirt cheapie price vs it's decent sound, this litte no-name New Yorker DAC is built in a small all-aluminum box so rigid & strong with 'seamless' corner joints looked like 100% watertight !!!!

So gratified !

Jack L

mememe2's picture

"$10,500 without internal storage". Two hoary homilies come to mind - 1. More money than brains and 2. You can put lipstick on a pig but it's still just a pig.

cgh's picture

Knowing nothing about the manufacturing process I was surprised, many years ago, to learn how expensive it is to make the box. I happened to be at a manufacturer's plant in CO after a RMAF when these parts came back from being dipped in acid and anodized.

Anyway, that's an attractive box IMO. The top reminds me of those popular pictures attempting to explain general relativity (curvature related to stress energy). Guessing it isn't cheap to make.

Jack L's picture

Hi

So comparing the "off-the-shelf" like fabrication quality of its inart, how much as a consumer like you, would guess to pay for the for the box alone ? Say 60% ??

Are we paying our hard-erned money for the music or its "attractive" box ?

By the same token, the dirt dirt cheap price I paid for my basic 24bit192KHz DAC of New York which sounds so decent, is built in a small "water-tight" aluminum box strong & rigid like a miniature tank. Where the manufacturer got the money to cover the cost of the box alone ??

Jack L

Jack L's picture

Hi

So comparing the "off-the-shelf" like fabrication quality of its inart, how much as a consumer like you, would guess to pay for the for the box alone ? Say 60% ??

Are we paying our hard-erned money for the music or its "attractive" box ?

By the same token, the dirt dirt cheap price I paid for my basic 24bit192KHz DAC of New York which sounds so decent, is built in a small "water-tight" aluminum box strong & rigid like a miniature tank. Where the manufacturer got the money to cover the cost of the box alone ??

Jack L

partain's picture

Unlike in the political universe , where never do promises of benefits "trickling down" come to fruition , Trickling down is inevitable in electronics.
Good thing.
I'd be willing to pay $700.00 , or so .

AaronGarrett's picture

I have one and my experience exactly mirrors JA. On low resolution material like streaming radio, which I listen to a lot, the difference is enormous upsampled via AES/EBU. Stuff I couldn't listen to I now really enjoy. For me this alone is worth it, I can enjoy a lot more music than I could without the MU-1. In addition for Native DSD it is great. And although JA didn't mention it (because it is not presently a feature) it will be able to do FM radio as well and be a very full-functioning digital preamp.

But as JA says also there are a lot of other very serviceable and cheaper solutions if this isn't an issue for you.

davemill's picture

I am looking forward to the release of the Boulder 812 which will additional provide balanced analog inputs and will be at a LOWER price point. I refuse to spent that amount for this type of device unless it is engineered and manufactured in the US which the 812will be and will no doubt perform extraordinary well.

Dear Stereophile Administrator, the CAPCHA authentication process at least for MacOS and iOS devices using Safari needs to be fixed. For at least six months, I have always had to use the forgotten password process to log in even though I am entering the correct password. This is a security issue.

Foottapper's picture

Hi John, thanks for the review. Since a couple of months I’m thrilled to have the MU1 at home, just love the ease of use ánd jaw dropping sound. Any chance that you’ll review the LS1be’s?

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