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:
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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:
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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:
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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.

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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):
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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 :-)

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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!

Sunday, 24 February 2013

MEASUREMENTS: Logitech Touch TT3 Mod.

Here's some data on my Touch with Soundcheck's Touch Toolbox 3.0 (http://soundcheck-audio.blogspot.ca/...oolbox-30.html) software mod applied.

Before I start, I just want to say that over the years I have not been involved in any of the discussions around this mod or the merits of it. Even though I do not necessarily agree with many of Soundcheck's comments on his site, I do appreciate his work in putting it together and creating the install script which was easy to run; it's always good to have hobbyists experimenting with stuff and it's interesting to see the feedback from users.

I followed his instructions to turn off the plug-ins, change to server-side decoding of FLAC in the "File Types" tab, "No Volume Adjustment", etc... As per instructions, WinSCP used to transfer the script and PuTTY for logging into the Touch.

I downloaded the script with 'wireless LAN deactivated' but noticed in the status screen that WiFi was labeled as "enabled" still (not sure if this means it's on or off!), so I used the 'tt -w' to turn off (or on) the WiFi status for good measure during a few of the measurements. Here's the screenshot of the "status" output for the "NoWiFi" condition in my charts (in retrospect, I think the modification turned off the WiFi, so when I 'disabled' the modification, it means I must have turned it on... not that it makes any difference as results show):


I also wanted to test the analogue output with "tt -o 1" but I could not get analogue output to work even though the status screen said it was enable. If anything, one would expect that turning off the screen, no wifi, server side decoding may drop the analogue noise floor maybe a few dB's... Oh well, I guess anyone who would go through this amount of modding would not be using the internal DAC anyways.

Procedure same as tests in previous posts, here's the result from the Touch+TT3 --> ASUS Essence 1 --> XLR cable --> E-Mu 0404USB:

16/44:
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16/44 THD graph:


24/96:
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24/96 THD graph:


The first column of each table is the stock Touch using the coaxial output (proper shielded coaxial cable of course).

Conclusion:
I see no difference with the Touch as digital transport despite screen off, no WiFi, server side decoding on these objective measurements. Subjectively, likewise, the Touch sounds great played through the Essence 1... Loving the sound of some Depeche Mode as I'm typing here with the mod still installed. I can see how not having the screen on and the ability to "touch the Touch" to make track selections would annoy me after awhile :-).

At least in my case with this specific DAC, the Touch Toolbox 3.0 mod made no difference to measurements even down to below -110dB noise floor.

MEASUREMENTS: Logitech Touch as transport!


The follow was a post I made of the Squeezebox Forum a few weeks back to hopefully answer the question of: How well does the Touch function as a digital transport?

Setup:
All the results here are made with the Touch with Triode's EDO firmware installed. For the sake of clarity, when I indicate a test was run in "EDO mode", this means it's the "digital only" mode, otherwise I'm referring to the default "digital + analogue" mode. For those wondering, there was no difference in measurements between stock firmware and with the EDO firmware installed.

The Touch was connected by ethernet to the basement music server --> either TosLink or coax out --> ASUS Xonar Essence 1 DAC --> XLR cables --> E-MU 0404 USB for measurement.

As previously measured, the balanced XLR output from the Essence One has so far given me the best electrical noise suppression and lowest noise floor, the Touch was used as the digital transport for this system. I then played the RightMark calibration, and test tones off the Touch and measured the analogue out from the Essence 1.

About the digital cables:
TosLink - cheap "VITonet" labelled plastic fibre cable - no idea where I got this, if I bought it, would likely be <$10 at local supplies store. Pretty thin and flimsy looking but gives a good tight connection with the ends. You can see this cable in the picture above just to the right of the Touch.

Coaxial - this gave me an opportunity to try a simple unshielded 3' stereo audio RCA cable (zip chord that I never used supplied with an old DVD player! forget any impedance matching or electrical shielding) vs. an actual shielded 6' coaxial cable "Acoustic Research Pro Series" I bought 10 years ago for ~$20.

I unplugged the Essence 1's USB cable from the computer during these tests to avoid potential noise pollution. Also, when testing the TosLink, the coaxial SPDIF was not connected.

First off, 16/44:
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Nothing to see here in terms of the Touch as transport! Essentially perfect measurements... The 1st column is just the audio played to the Essence 1 through USB 2 (note there's something wrong with the IM value here - I suspect it was a spurious error from this run). Whether I used TosLink, cheap RCA, actual coaxial to connect to the Essence 1 from the Touch did not matter.

Now, 24/96 (standard "digital + analogue" mode):
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Hmmm, not unexpectedly, the "RCA as coaxial" is the stand out here. Slightly reduced noise floor (~1 dB), reduced dynamic range (~2 dB), mildly worse stereo crosstalk.

How about 24/96 in "EDO mode" with the analogue output turned off?
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Essentially the same as the standard mode. It appears that turning off the analogue output circuitry (or at least silencing it) does not affect the test results in any meaningful way. Again, the RCA cable performance is inferior to a proper shielded coaxial cable. However one has to realize that at this level of performance, the difference is really so minor that it's unlikely anyone would be able to tell a difference from listening! To give you an idea, here's the THD plot, notice how little difference there is with the RCA cable (cyan) just rising over the others like around the 2-10kHz range.

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Conclusion so far:
1. 16/44 performance is beyond reproach according to these tests.
2. 24/96 performance likewise is excellent. Starting to see the limitations of an unshielded cable connected to the coaxial SPDIF but even in such an extreme situation, the rise in noise floor is likely inaudible.
3. Turning off the analogue output does not appear to improve the quality of the digital transport.

Now it's time to talk 24/192 with the Touch with EDO plugin. Thank you Triode - amazing plugin/kernel!

Results:
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What I find impressive here is the fact that TosLink to the Essence 1 worked at 24/192!!! In fact, that picture of the Touch in the previous post playing the 24/192 John Coltrane's "Blue Train" (Classic Records HDAD release from 2001) was through the TosLink (you can see the 192kHz LED lit up on the Essence 1). This is why I'm very impressed by the components used in the Touch; kudos to Logitech and ASUS! Over the years, this is the first time I've been able to play 24/192 for hours without obvious clicks/pops/disruptions even with an inexpensive plastic cable. To show the TosLink result above wasn't a "one-off", here's a series of 4 runs with the TosLink done over about 2 hours - notice the inter-test reliability.

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Like with the 24/96 tests, the cheap RCA cable is showing its limits even more with measurably increased noise floor (10 dB worse!) from the lack of shielding and possibly data errors as the speed of data transfer doubles. Another interesting phenomenon is that even the shielded coaxial cable has a measurably higher noise floor compared to the TosLink by about 2dB. Would an expensive coaxial cable improve this? Possible I guess if the shielding is excellent, but even so, would anyone ever notice at around -110dB!?

Another observation with this test is that the noise level, dynamic range, and stereo crosstalk are all WORSE than 24/96. Every piece of equipment here from the E-Mu, to Essence 1, to Touch are running at max. specifications so the system is running at it's limit.

Here's the THD graph showing the increase in noise with the coaxial interface - el cheapo RCA (cyan) is looking "bad" here:
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Conclusion:
1. Thanks again to Triode for the EDO plugin/kernel. It works beautifully and in my system with TosLink working, the Touch measures within 1-2 dB in terms of noise level, dynamic range, and stereo crosstalk compared to a direct USB connection to the DAC for 24/192 playback!

2. If you can get the TosLink to work, you've set yourself free from electrical noise with "galvanic isolation" of the Touch and DAC. Again, the fact that I could get TosLink 24/192 to work reliably between the Touch and Essence One really is impressive and speaks well of the equipment.

3. A recurring theme in these tests is that of ELECTRICAL NOISE. Coaxial SPDIF cables need good shielding at 24/192!

4. 24/192 does not measure as well in my system as 24/96. Writers like Lavry and xiph.org ("24/192 Music Downloads Make No Sense") have already eloquently documented their opinions against 24/192 and I guess I can echo their concerns with the gear I'm using for these tests... Firstly, between 24/96 and 24/192, the difference is ultrasonic; do we demand high-end SLR digital cameras to also capture ultraviolet light? (Sure, you might want to do this for specific scientific reasons.) Secondly, other than a handful of albums usually from smaller labels like 2L, Reference and Linn, I have rarely come across truly native 24/192 (or 24/176) recordings. IMO, it also makes no sense to buy stuff like DSD64 converted to 24/176 such as many of the HDTracks offers.

Addendum: Feb 27, 2013
Thanks to slimdevices forum member "tpaxadpom" who measured the digital output with the AP2722 unit:
SPDIF RCA 377.3 - 324.5 ps
Toslink 1.604 ns

RCA much better in terms of jitter measurements.

MEASUREMENTS: Logitech Squeezebox Touch. [Updated 2013-06-22]


I got this unit late last year lightly used when Logitech announced the Touch's discontinuation. I notice it is quite hard to get one of these now and they're commanding quite an elevated price on eBay!

- Internal DAC chip: AKM4420

Setup: i7 computer system - same as Essence One. Analogue output from Touch going into the E-MU 0404USB for measurements.

Oscilloscope measurement of 1kHz square wave, 0dBFS off the analogue RCA output:
Nice clean waveform. 2.92V peak voltage. No significant channel imbalance noted.

Standard linear phase oversampling digital filter impulse response (16/44). Absolute polarity maintained.

RightMark Results:
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Mostly better results all around compared to the SB3. Frequency response within tighter range over the 20-20kHz spectrum, noise levels 1 dB lower in the 16-bit domain (as if it could go any lower!?), and about -4dB lower with 24-bit data giving the Touch DAC about 17.5 bits of dynamic range. Interestingly, the stereo crosstalk is a bit higher in the Touch vs. SB3 by about 6-8 dB (remember, it's still down at -90dB).

Notice no significant difference between WiFi and wired through the ethernet.

Frequency Response:






16-bit audio vs. 24-bit audio. Looks good. Less bass drop-off than the SB3 with my equipment.


Noise Floor:




 THD Graphs:




Jitter (Dunn J-Test, WiFi):
16-bit:

24-bit:


Analogue outputs look very clean.

Summary:
I guess the only surprise is that the stereo crosstalk is higher in the Touch than the SB3. Otherwise, audio quality seems superior - it can obviously handle 96kHz natively (up to 192kHz with the EDO plug-in as a digital transport), and flatter frequency response especially in the low bass could be audible.

Again, assuming the WiFi strength is reliable and you're not constantly rebuffering, I see no indication that sound quality is negatively impacted by going wireless.

Subjectively, I like the Touch's sound. These days, it powers my bedroom system with SONY amp and Tannoy mX2 bookshelf speakers I got about 10 years ago. For what it is, I can't complain about these analogue output results - very competent! Although you can get better measuring noise floor, dynamic range, etc. with an outboard DAC, the Touch in its stock form is already very impressive and it would be wise to do some A-B testing before thinking an expensive DAC will improve the sound much!

For what you get, the bang-for-the-buck from this little device is fantastic and a shame really that it has been discontinued.

MEASUREMENTS: "Slim Devices" Squeezebox 3 [Updated June 25, 2013]

Next up - my classic "Slim Devices" Squeezebox 3 (I believe this is one of the "first run" units; I was on a wait list at introduction):
- Internal DAC chip: TI/BB PCM1748E


Setup: i7 computer system with the analogue outputs of SB3 --> E-MU 0404USB. Details for this setup is same as Essence One tests.

Here's the oscilloscope plot of a 1kHz square wave at 0dBFS off the analogue outputs. Square wave have a slight downward slant. Peak voltage 2.64V. Nice channel balance (yellow = right, blue = left).

Standard linear phase digital reconstruction filter.

RESULTS:

First 2 columns are the stock SB3+stock wallwart connected to my basement music server by WiFi. Notice that 24-bit data does result in dropping of the noise floor by ~6dB. It looks like the good ol' SB3 internal DAC is capable of about 17-bit resolution when fed with 24-bits. Note that the old Stereophile review from 2006 did not measure 24-bit performance.

Second 2 columns are the same setup but with the ethernet (hooked up to my DLink gigabit switch 6 feet away). Essentially no difference compared to the WiFi.

Final column is with the SB3 over WiFi but the *SB Touch wallwart*. I see folks here talking about the crappy wallwart (true, the UNIFIVE wallwart looks and feels nasty compared to the one that came with the Touch!). I fed the 24-bit data and the result is essentially the same as the UNIFIVE. Based on these measurements, I don't see any evidence that the Touch wallwart would improve the stock SB3 performace.

Frequency Response:


Decent - obviously not as flat as Essence One from 20Hz-20kHz...

Noise Floor:


16-bit data obviously not as good as 24-bits. No difference between the WiFi vs. Ethernet groups.

THD Graph:


Dunn J-Test:
16-bit (16/44) -



24-bit (24/48) - 

CONCLUSION:

1. The SB3 can benefit from 24-bit "hi-res" audio. Whether you can hear the extra 5-6dB is your problem :-)
2. I see no evidence that a Touch wallwart would improve the performance over the cheap stock power supply. Who know is the multi-hundred $$$ or linear power supplies make a difference...
3. No evidence that running in WiFi mode will add any noise to the SB3 output.
4. The Dunn J-Test is demonstrating minimal jitter.