Monday, 25 February 2013

MEASUREMENTS: Logitech Squeezebox Transporter [Updated June 26, 2013]


It's Squeezebox Transporter time!


In order to do the measurements, I brought the gear downstairs to the basement which is an electrically quieter environment. There's a Belkin PureAV PF60 power center there for all the equipment. Also, the measuring computer is now the AMD Phenom X4 laptop with Win 8 usually used by my kids :-). The laptop was running on battery - I could detect a 0.5dB difference with the AC adaptor plugged in down at the -110dB noise level.

One note about the XLR measurements you'll notice - the THD levels are a bit higher than RCA. I believe this is a result of the fact that the E-Mu 0404USB could not handle the XLR voltage from the Transporter and I had to use the analogue attenuators to (just barely!) avoid clipping.

Lets start with the 44kHz signal:
Name:  44_Results.png
Views: 153
Size:  29.6 KB

Undoubtedly, the XLR output is significantly better than RCA. One observation is that through the RCA's, the stereo crosstalk remained around -90dB whether the signal was 16 or 24-bits. I'm not sure if this is the limit of the Transporter itself, or has to do with the cables I used - a pair of AudioQuest 6' interconnects. I don't remember which model of AudioQuests these were (bought a few years ago in a moment of weakness :-) but they are longer than the 3' I had been using to measure upstairs.

Now for 24/96:
Name:  96_Results.png
Views: 152
Size:  29.3 KB

Again, we see the -90dB stereo crosstalk limit with the RCA output. XLR's measure is fantastic! Likely hitting the performance limits of the E-MU 0404USB and ~3dB better than the Essence One (of course the E1 did not have the benefits of a power filter or low noise environment of the laptop running on battery).

The WiFi router was in the same room as the Transporter hence the 90+% wireless strength. No difference in the measurements whether WiFi or ethernet.

To show in graph form the difference in noise floor between the RCA and XLR:

Notice the noise spikes like at 60Hz using the RCA cable (the AQ construction seems to be shielded but can't confirm unless I cut it open!).

Conclusion:
1. Overall the Transporter measures well! Phenomenal XLR performance - best I have been able to measure so far; >19-bit dynamic range.
2. A bit unclear about that stereo crosstalk measurement with RCA however. A bit higher than I'd have expected. Might need to try a different cable and see... (In case anyone wondering, I have not opened up the Transporter to change the unbalanced volume attenuation.) --- SEE ADDENDUM: I believe it's the cable!

ADDENDUM - (Cables do make a difference :-)

Further exploration of the stereo crosstalk issue shows that it likely was the cable afterall! I switched the analogue out from the AudioQuest (can't confirm but the cable looks like the current "Yosemite" model on their web page) to a pair of old 6' Tributaries interconnects (probably 50% the cost). As seen below the Tributaries improved stereo crosstalk by ~2.5dB:
Name:  AQ_vs._Tributaries.jpg
Views: 144
Size:  26.3 KB

Here's how the graph looks (AQ [white] vs. Tributaries):


Furthermore we're starting to see that 24-bit audio is starting to show better separation compared to the 16-bit data with the Tributaries suggesting that the cable was the limiting factor! I expect a good 3' cable would improvement the measurement even further. At this point then, I believe the Transporter's RCA stereo crosstalk is just fine.

Interesting that the more expensive AudioQuest measured worse than the Tributaries in this setup. As a result of this, I'm going to demote the AQ's to my CD player - something I would never know to do unless I ran this objective test.

------

Before I leave the Transporter alone... I wanted to see if turning on the TosLink effects loop affected measurements. Normally, I have the Transporter --> TosLink --> Behringer DEQ2496 (room EQ) --> TosLink --> Transporter as DAC, so it'd be nice to know that the DEQ in digital mode doesn't affect the final sound (tested at 24/96).

With the DEQ2496 on bypass mode (ie. no room EQ processing):
Name:  Tributaries_RCA_-_TosLink_Effects_Off_and_On.png
Views: 251
Size:  25.2 KB

Using the Tributaries RCA cable as output, no difference whether the DEQ2496 was digitally in line or not. Note that I used rather generic TosLinks - well constructed relatively thick plastic optical cables bought on sale for $10 each. Alas, by this time I had disconnected the XLR's and I didn't care to disrupt the Transporter setup again :-)

------

Transporter Jitter measurements (Dunn J-Test 24/48, XLR):



Direct from the analogue output, this looks good!  The usual beautiful Transporter jitter plot. The 6 tiny spikes/sidebands are estimated as <300ps total (I think Stereophile measured 230-270ps) - nice corroboration!

Now what happens with the DEQ2496 in line (remember, the digital data is now going through 2 TosLink cables as described above)?
Obviously quite a bit more jitter has been injected by the Behringer! My estimate looking at the top 8 sidebands suggests that the jitter level now is 2ns using some measurements in WaveSpectra!

Since I can just turn the digital loop on and off, I can do instantaneous A-B'ing of the sound. Even in this condition, I cannot say the clearly increased jitter is at all noticeable. What can I say, even knowing this I'm just fine with keeping the DEQ2496 in line and use the room EQ function since *that* is audible! At least now I can say I've done an A-B test examining the effect of 2ns jitter for myself.

Addendum: Feb 27, 2013
Thanks to slimdevices forum member "tpaxadpom" who measured the digital output with the AP2722 unit:
AES/EBU 377.3-424.5 ps
SPDIF RCA 566 ps
SPDIF BNC 283-330.2 ps (rca cable with 2 bnc adapters yielded the same results)
Toslink 1.462 - 4.103 ns depending on the cable used. I've tested 4 or 5 different toslink cables.

Looks like the Transporter's BNC connection is the winner followed by AES/EBU. TosLink worst for jitter not surprisingly.

Addendum: March 6, 2013
Got some AES/EBU digital cables - here are the measurements.

Addendum: June 26, 2013
As part of the transport measurements, I decided to have a closer look at the Transporter. Here's some more data to consider:
Lovely 24/44 square wave at 0dBFS off the RCA output. Peak voltage of 2.95V. Very nice channel balance.

Impulse response (16/44):
This is the standard "sharp" filter. Linear phase. Absolute phase maintained.

When you set to "slow" roll-off, look what happens:
Wow... Barely any pre and post-ringing! However, clearly to achieve this, roll-off is expected to be very significant.

The "big board" RightMark summary - all based on RCA analogue output:
Look at the 16/44 frequency response; clearly roll-off is quite significant. Here's the graph:
You see the response deviating significantly by about 8kHz and more than -1dB by 15kHz. For good 'youngish' ears, that's significant.

This is what 24-bit buys you in terms of noise floor - remember this is with RCA output, expected to be even better with the XLR:

At 24/96, the filters are still quite different, but inaudible difference for anyone but cats, dogs and machines :-):

RCA analogue output Dunn J-Test:
16-bit (16/44):

24-bit (24/48):

Summary: I remain very impressed with the Transporter. Kudos to Sean Adams and the Slimdevices team back in the day. Technically a beautifully designed machine and it remains my primary digital front end in the listen room. I was a bit surprised by the slope of the slow roll-off - much more than I thought!

5 comments:

  1. Hey Archimago,

    ...wanted to let you know I sure appreciated your analysis and commentary. I used a similar setup to yours for years: Transporter -> Behringer DEQ2496 -> Transporter. AES for the loop. I recently modified my setup, feeding s/pdif directly to a NAD M2. The Behringer is now in loop using the M2 (using, ironically, optical).

    ReplyDelete
    Replies
    1. Nice setup Thomas!

      Wonder if you've done an A-B comparison of the M2-Behringer loop comparing the M2 direct vs. M2-Behringer with Behringer on bypass. As noted in my later Transporter-Behringer AES/EBU post, there was a measurable decrease in jitter compared to TosLink. I never could hear the difference however.

      Delete
  2. hi i Don't know why but this version of Windows sounded much better
    so i duméed my install cause is a insider preview 17763.17 updated from 1803
    https://hotelattraction.wixsite.com/windowsaudiophile

    enjoy and thank you for ALL tour work

    ReplyDelete


  3. Great post you shared, you have now become top of my list. You were unknown to me before but have found your content to be fantastic.

    So great work for informing us of the possibilities and following a certain path.

    I really appreciate your hard work an giving us some information and inspiring others to follow.

    Thanks so much.

    I hope for more post in the future.
    Open Frame Touch Monitor

    ReplyDelete