Friday, 30 August 2013

Greetings from Asia...

Thought I'd put up a quick post since it's the end of August...

Been traveling around a few countries over the last few weeks with the family. I've kept my eyes open to see if I can spot some good audio gear but so far no luck. Beijing for example has huge malls of IT gear - computers, cameras, DIY pieces, electric toys, surveillance equipment, and massive floors of flat screen TV's. Barely anything hi-fi to be found. Maybe I just didn't hit the right stores!

One thing that's quite clear these days, with the year-on-year inflation running close to 3% over the last few years, with inflation up to 8%/year back around 2006-2007, Beijing (large cities in China in general) sure isn't cheap these days for most things from a foreigner's perspective. The cost of housing/condos these days would be horribly prohibitive for middle-class young folks to set up a decent sound room.

Note that I did run into a few speakers that looked like clones of the B&W Nautilus 801 of questionable workmanship...  Otherwise, what I saw looked like quite low-end receivers and the ubiquitous soundbars meant for small home theatres.



I've been to Singapore a number of times, about every 2-3 years for personal travel and work-related duties. It's amazing the development over the last few years...  I guess opening up for gambling does tend to draw in liquidity :-). This despite decades of bans against gambling out of a strong moral stance. Behold, the Marina Bay Sands and the "supertrees" out at the Gardens By The Bay right across from it:



For tonight, I sign off from a spotty WiFi connection here in Ao Nang, the tourist village close to Krabi, Thailand. Some of the islands around here got hit pretty hard by the tsunami back in 2004.




I'll be back in Singapore next week and hope to hit The Adelphi for some hi-fi auditioning... Wishing all a good Labour Day long weekend ahead (in N. America at least) :-).


Sunday, 11 August 2013

MEASUREMENTS: WD TV Live - A look at (and listen to) the digital "low end".

I'm sure we've all seen these ubiquitous devices at the local BestBuy, Costco, Walmart, etc.



Even as an "audiophile", you might be tempted to purchase one for streaming audio/video to the den, basement, bedroom, etc... As you can see, on the back, from right to left, there's the little phono plug which functions as composite video/stereo audio (comes with a supplied cable), then a second USB port (one up front), HDMI, 10/100 ethernet, TosLink, and power plug to the wallwart.

It's mass market, inexpensive (this particular no-frills model usually goes for <$100), and there are a number of equivalent digital streamers out there with a similar feature set (Patriot, Roku, D-Link, Pivos, etc.). Although it's primarily meant to be a digital HDMI transport, I wanted to see what this could offer for the audio lover... In my mind, "mass market" and "inexpensive" are not bad characteristics. IMO consumers should be thrilled to find a technically good/excellent product at this price point and ease of availability if they can! Furthermore, I think it's worth looking at the "low end" to understand just what is gained with better quality gear more to the "high end".

The P/N at the bottom of the unit was WDBHG70000NBK-01. This was bought back in 2011 by my brother-in-law so current models may have hardware differences. I tried to open the unit up to have a look inside but there are no screws and I really did not want to potentially damage the aesthetics (it's not mine after all!). I see Legit Reviews opened an even earlier unit back in 2009 and found a Sigma SMP8655 SoC inside but didn't comment on what DAC was being used. I imagine this model would be based on something similar. Legit Reviews has another article on this model but no discussion on the chipset.

Let's see objectively then what this little device can do...

I. Stereo analogue output:

Let us first start with looking at what's coming out of that composite/stereo RCA cable from the built-in DAC. The supplied phono-to-RCA cable is cheap and thin but functional, about 3 feet long.

Setup:
Test signals & music (FLAC) on high speed ADATA USB3 stick --> WD TV (front USB) --> supplied audio/video RCA cable --> E-MU 0404USB --> shielded USB --> Win8 test laptop

WD TV firmware (latest): 1.16.13

I'm using a high speed 32GB USB3 stick. Although it's a USB2 port, I did not run into any troubles. All audio was encoded in FLAC lossless compression. This setup should provide the best audio quality from the unit (ie. no streaming issues or risk of lossy transcoding). There's no digital volume control to affect the sound quality as far as I can tell. I mainly want to see just how objectively accurate this device can decode audio through its own DAC and as an optical TosLink transport later.

Here's the 0dBFS 1kHz square wave through the oscilloscope:
Good channel balance and credible square wave. Peak voltage at ~1.23V. Notice the plateau isn't flat suggesting imperfections in the voltage regulation.

Impulse response:

Somewhat unexpected, looks like an intermediate phase upsampling digital filter was used which decreases the pre-ringing for a more extended post-ring. Absolute polarity maintained.

RightMark:
Here is a summary of the "big board" - I've included data from the Squeezebox Touch and with the Transporter representing the kind of result one usually associates with "high end" products:

Basically we see that this device is capable of 16-bit resolution with marginal improvement going to 24-bit data. Interestingly, it seems to be handling 88kHz okay - good frequency extension beyond 30kHz:


But, 96kHz and above (I also tested 192kHz) looks like it's being downsampled to 48kHz (verified when I did the digital tests below):

Odd, I wonder why they didn't support 96kHz since it's not that much higher than 88kHz and arguably more useful.

A few comparison charts at 24/48 then:
Frequency Response:

Noise level:

THD:

Clearly the WD TV Live cannot compete with either Squeezebox products technically. Frequency response is down to -3dB by 20Hz which can result in audibly weak bass. Also, there's some kind of high frequency noise at around 16kHz.

Jitter:
As I have demonstrated in the past, jitter (as can be measured with the Dunn J-Test) is usually NOT an issue unless there's an S/PDIF interface in the way.  This is true with the WD TV Live:

16-bit Dunn J-Test:

24-bit Dunn J-Test:
No anomalous sidebands with the J-Test at all. No surprise... However, that nasty 16 kHz noise can be seen in the graphs above!

1kHz -90.3dB Waveforms:
So, what does the 1kHz -90dB undithered 16-bit waveform look like?
Hmmm. As you can see the left (green) channel is very noisy compared to the right (blue). In fact, you can generally make out the 3 voltage levels in the blue tracing suggesting good representation of a 16-bit bit-perfect signal. I determined that the 16kHz noise was primarily in that right channel...  Ugly, but arguably still better than the TDA1543 NOS DAC I showed in the previous post. Remember that this is zoomed in looking at a -90dBFS signal.

Here's the same waveform in 24-bits:
Again, noisy left (green) channel with a smoother sine wave with the right (blue) tracing.

Okay... Obviously the analogue output leaves much to be desired straight out of the WD TV Live.


II. As S/PDIF TosLink Digital Transport:

Setup:
Test signals & music (FLAC) on high speed ADATA USB3 stick --> WD TV (front USB) --> 9' generic plastic TosLink --> ASUS Essence One DAC --> 3' shielded RCA --> E-MU 0404USB --> shielded USB --> Win8 test laptop

I tested the WD TV Live with audio set as "Stereo" as well as "Digital TosLink Pass Through" in the Setup menu and noticed no difference for regular PCM audio.

RightMark:
The results are clearly improved over the analogue output above. Basically, these numbers are in line with the usual result out of the Essence One using unbalanced RCA cables. (Note that some of my other tests are with XLR balanced cables which usually improves dynamic range by about 3dB.)

You might be curious why there's no 24/88 result...  Interestingly, even though 24/88 could be played with the analogue output, it doesn't output a digital signal at that sample rate! I can see the Essence One going into 24/88 mode but there's only silence! I don't believe this is an issue with the DAC since with the Squeezebox Touch (EDO kernel), I am able to play up to 24/192 using the TosLink interface (most device pairs are limited to 24/96 with TosLink).

Again, 24/96 is downsampled to 24/48:

Let's now compare the 24/48 result with some of  the other transport devices I used in my previous post comparing various digital transports connected to the ASUS DAC via TosLink:

Frequency response:

Notice the slight variability between the devices up in the high frequency range.  Again, my suspicion is that this is due to slight timing differences in the S/PDIF signal. Zoomed in, you see that the WD TV Live is actually right at the middle of the pack: 

Noise Level:

THD:

Stereo Crosstalk:

As you can see, other than that slight frequency response difference, the other tests show no significant difference between the digital transports with the ASUS Essence One DAC. Unless you have better than 0.1dB hearing acuity up at 18kHz, that slight frequency response variance between the devices should not be significant.

Jitter:
16-bit Dunn J-Test:

24-bit Dunn J-Test:

Well, there's the S/PDIF jitter for you. Jitter modulation pattern is obvious which means we're looking at a bit-perfect signal from the WD TV. 24-bit tracing is clearly more jittery than at 16-bits. The WD TV Live's digital output is more jittery than the previous devices tested (you can find those graphs in this post).

1kHz -90dB Waveforms:
16-bit undithered:

24-bit undithered:

Much better looking zoomed-in waveforms - as expected from the Essence One DAC. Only a bit-perfect source would be able to produce that 16-bit undithered waveform morphology above.

III. Summary:

So, this is what a $100 streamer can do in terms of audio these days. On the whole, not too bad actually! Some level of inaccuracy is expected in the objective analysis; not surprising given the compromises at this price point for something that's targeted more for digital video playback/streaming.

In terms of analogue audio quality directly off the unit:
1. It's a 16-bit internal DAC that's demonstrably noisy down at the LSB level. Although it has aspirations for 24-bits, there's really no significant benefit.

2. It's curiously able to manage 88kHz but anything above gets downsampled. IMO might as well stay with 44 & 48kHz.

3. The frequency response is hampered by bass roll-off of a greater magnitude than I'd be comfortable with. This IMO is the most audible effect and results in audibly "weak" bass.

4. There are suggestions of power supply issues with the square wave stability, and electrical noise up at 16kHz especially affecting the right channel in this sample I'm testing.

5. If a person were to complain about the sound quality of the analogue output, please don't point your finger at the dreaded jitter...  The issues above are much more significant.

As a digital transport using TosLink to the ASUS Essence One DAC:
1. RightMark results off the ASUS DAC are completely in keeping with the other bit-perfect transport devices previously tested (like the Touch, Transporter, Receiver, SB3, laptop-to-CM6631A, etc...)

2. This device is strangely incapable of sending an 88kHz signal to my ASUS Essence One even though it can decode 24/88 with the analogue out. Again, 24/96 and above gets downsampled to 24/48. More reason to just stay with 44 and 48kHz sampling rates.

3. S/PDIF TosLink jitter is demonstrably elevated compared to the other devices. This is the most technically anomalous finding (apart from the limited/idiosyncratic sampling rate support).

Subjectively, I had a listen to the analogue output of the WD TV Live with my Sennheiser HD800 headphones over a couple of nights. Despite the measurable limitations, it actually doesn't sound bad. With softer tracks like Queen's Love Of My Life (DCC Remaster) and Tracy Chapman's Fast Car, it sounds reasonably detailed except for a bit of harshness in the upper frequencies ("brittle" sounding high-hats and cymbals for example on a few of the tracks). With louder/bass-heavy tracks like AC/DC's Thunderstruck or Prodigy's Smack My Bitch Up, it doesn't "rock" as hard but most of the bass is still there; just not as accentuated as I'm normally used to. On loud, compressed tracks like Tyler Bates' To Victory ('300' soundtrack), things seem congested but not unenjoyable.

Once I switched to the digital TosLink output, it sounded like the ASUS Essence One. Nice and clear, good bass definition, quiet background. Even though higher amount of jitter is demonstrated with the J-Test compared to the other devices tested, I remain unconvinced that it's audible in regular music. I agree that with a S/PDIF interface, bits are not just bits but include timing inaccuracies (jitter), however I remain unimpressed that jitter of the magnitude I'm measuring with the WD TV Live negatively affects audio quality in a meaningful fashion.

So far, I'm still of the opinion that bit-perfect digital transports sound essentially the same when connected to a decent external DAC (consistent with the results here recently and here where I tested different laptops awhile back).

Remember that for these tests, I'm just using audio stored on a USB thumb drive. I did not set up the WD TV Live to stream off the ethernet/WiFi so cannot comment on how that would sound.

Music selection tonight: Time for a little "latin jazz"? Poncho Sanchez's "Freedom Sound" (1997) and "Cambios" (1991) are great for a warm summer night :-). Well recorded, dynamic albums with sweet music...

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Guys, even though I just got back from a trip, I'm heading off to another soon :-). Busy summer with the family. Have a great August! I hope to check out some audiophile shops in Singapore this time around like The Adelphi.

Saturday, 27 July 2013

MEASUREMENTS: DAC "Waveform Peeping" - the -90.3dB 16-bit LSB Test...


When it comes to technological "toys", I've vacillated over the years between the accumulation of digital photography gear and audio stuff... As I'm sure many of you know, "pixel peeping" is the act of "using 100% crops and similar techniques to identify flaws that have no effect on the photograph under real-world conditions" (Google web definition). Back in the "old" days (like a decade ago), the act of pixel peeping wasn't all that unreasonable since the differences visible could be demonstrated on photo-enlargements. When I was using my old Nikon D70 with 6 megapixels, sharpness at the pixel level was a significant consideration with moderate enlargements like 13"x19"; imperfections like moiré could be seen in the final product as well. Monitor resolution wasn't that high back then either so fine details were easily obscured.

Fast forward these days and I'm now using the Nikon D800. At 36 megapixels viewed on a >2MP monitor; unless I'm printing huge enlargements, there really is little need to "zoom" down into the 1:1 pixel level to appreciate a high quality image... Sure, sometimes it's just fun to see how much detail has been captured especially when evaluating different lenses or to show off each hair follicle, but for the most part, "pixel peeping" has become quite unnecessary.

Although in daily usage, one might not need to "peep" anymore, if one were to publish camera body or lens reviews, any reviewer these days "worth their salt" would run the images through objective tests; including highly detailed "pixel level" tests or compare 1:1 images between cameras or lenses. Dynamic range, ISO-noise interaction, color accuracy tests, distortion characteristics (for lenses), effect of file formats (JPEG vs. RAW) of course all serve to complete the evaluation. The quality is so high these days among high-end cameras (SLR's, medium format digital backs...), it is with these detailed tests that we can fully appreciate the qualitative differences between top contenders. Subjective opinions in terms of the camera's touch-and-feel and user interface are important of course, but if you care about the potential image quality that can be captured, then objective tests are really really important. If you haven't already done so, just have a look at the camera reviews on www.dpreview.com and see how much work actually goes into what I respect as proper reviews of well engineered equipment! Also of interest, Hasselblad is trying to market "exotic" cameras at high prices by appealing to aesthetics (just look at the responses to see how people feel about that!). [Here's another one.] Is this what happens when technology matures and companies have difficulty competing on primarily technological merits?

I've often wondered why in the audio world, objective measures have so often been left out as part of the review process - especially as it comes to line-level devices like DACs. Maybe it's because digital audio matured earlier and we're going to see the same outcome with cameras one day. Around some forums, the mere mention of objective measures seems to be scoffed at - as if objectivism with audio gear is either "obsolete" or the sole domain of "high end" manufacturers with arcane tests out of reach of mere mortals. I know I'm digressing into "MUSINGS" territory here, but IMO, a good review needs to dig into the gear's objective properties so the reader can truly appreciate how it compares with other similar gear in order to have an informed opinion and gauge value as a (hopefully) well engineered piece of technology... Let's get back on track then with some "MEASUREMENTS".

For me, one of the most interesting "waveform peeping" tests consistently done by Stereophile over the decades on digital gear has been the undithered 1kHz sine wave test at -90.3dBFS. This is one of the most "microscopic" tests of DAC performance. It's simple and the result basically answers the question "can this DAC accurately reproduce the least significant bit (LSB) in a 16-bit audio signal?" At a glance one can tell at least 3 things:
1. Is the DAC "bit-perfect" down to that last 16th bit? (Assuming everything upstream is set up properly, you should see something resembling the 3 quantization "steps".)
2. Is the dynamic range at least 16 bits? If not, the waveform becomes obscured by excessive noise.
3. Are there anomalies to the waveform morphology to suggest "DC shifts" leading to "tilting" of the waveforms (power supply related issues). (For a good example of 60Hz low frequency noise effect, see the measurement of the Philips CDR880 Figure 7.)

The Stereophile website archive provides some lovely examples of this test dating back to the late 1980's such as the Philips LHH1000 from 1989 (check out Figure 5). How about the Naim NA CDS from 1992 (Figure 6) or the $8000 Mark Levinson No.35 DAC from 1993 (Figure 6, still not good). By 1995, we saw excellent performance like with the $9000 Krell KPS-20i (Figure 5). In a few years, by 1998, reasonable priced gear like the California Audio Labs CL-15 CD player was capable of similar accuracy at the $1500 price point. Since the millennium, this level of performance can easily be achieved within the $1000 price point and below (eg. the Rega Apollo from 2006). These days, the little Audioquest Dragonfly can do a reasonable job USB-powered at <$250 retail.

On the whole, this test has demonstrated the progression of improved accuracy over the years. State-of-the-art DACs like the MSB Diamond DAC IV (Stereophile October 2012, not on website) and Weiss DAC202 (Figure 6) are great examples of what this level of accuracy looks like (as opposed to expensive gear of questionable technical ability which I will not mention). IMO, well engineered CD/DVD/SACD/Blu-Ray/DACs these days claiming to be "high resolution" really should pass this test without issue. Nonetheless, there are recent devices apparently incapable of a low noise floor for whatever reason (eg. Abbingdon DP-777 Figure 15, surprisingly the recent Wadia 121 Decoding Computer Figure 6 didn't fare too well either).

I was curious whether I could run a similar test using my simple test gear... After all, so long as the DAC and measurement device can achieve >16-bits dynamic range reliably, one should be able to obtain a reasonably good set of measurements. So far, from what I've seen in the other tests, I should be able to reproduce this test with the E-MU 0404USB!

Here goes... Setup and procedure for the various DACs/streamers:
Test DAC --> shielded RCA --> E-MU 0404USB ADC --> shielded USB --> Win8 laptop

- I created an undithered 1.1025kHz sine wave at -90.31dBFS at 16/44. This is what an "ideal" waveform would look like with the usual Gibbs phenomenon (ringing) due to bandwidth restriction.
- Green is LEFT channel, Blue is RIGHT channel. Notice the phase inversion between the channels.

- For comparison, I also created the equivalent at 24-bit quantization:

- Capture the above at 24/88 with Audacity using the E-MU 0404USB. From previous tests, the E-MU functions very well at 2x sample rates (88 & 96kHz) with optimal dynamic range. Although not as good as a high precision oscilloscope used by Stereophile, this should be adequate to allow relative comparisons between different DACs. I used the analogue preamp on the E-MU to boost the signal by about 18dB to give me "more" amplitude to capture.
- As you can see above, I decided to plot the channels overlaid and inverted to compare precision of timing and amplitude.

Here are the results of this test on the various DACs I have around here:

TEAC UD-501 [2x BB PCM1795 circa 2009] SHARP filter:
16-bit undithered:


24-bit:

Clearly the TEAC has no problem with reproducing that least significant bit in the 16-bit signal. Also, obviously the resolution has improved significantly by going to 24-bits.

ASUS XONAR Essence One [2x BB PCM1795 c. 2009] (opamps upgraded to all LM4562):

Very nice... Notice a wee bit of channel imbalance - the left channel (blue) seems consistently louder than the right. Same internal DAC chip as the TEAC so similar level of performance expected.

Logitech Squeezebox Transporter [AKM4396 c. 2004]:

Nice! Not bad for a discontinued device from a computer peripheral manufacturer released in 2006, eh? ;-)
Of course, the Stereophile review demonstrated this nicely already...

Logitech Squeezebox Touch [AKM4420 c. 2007]:
WiFi (only 30% signal strength 2 floors up from router!):

Ethernet:

24-bit:
Three observations:
1. Clearly the Touch is noisier than the better DACs above. It's still capable of >16-bit dynamic range though.
2. Some DC shift is evident - look at the upward slope with the 24-bit sine wave and compare to the Transporter above. Maybe this could be improved with a better linear power supply than the stock switching wallwart I used... Not sure if an improvement would be audible however.
3. No substantial difference between WiFi and Ethernet. (No surprise; just thought I'd have a look to see if WiFi added much noise down at this level.)
N.B. Remember that this is still a pretty good result - we are looking at a waveform down at -90dBFS, or ~90 microvolts! Nice correlation with what Stereophile found (Figures 5 & 6) in terms of the Touch being a 'touch' more noisy than better DACs.

AUNE X1 Mark I [BB PCM1793 c. 2003] (using CM6631A USB-to-Coaxial S/PDIF, ASIO driver):

This is what can be achieved by a <$175 DAC off eBay direct from China these days (I bought this unit in early 2012). Notice that it's able to produce a cleaner analogue output than the Touch. But it's also not quite up to the standard of the TEAC, ASUS, or Transporter. Notice both a slight channel imbalance as well as mild amplitude fluctuations (again, possibly due to cheap wallwart). Hopefully the following zoomed out screenshots illustrates this well for comparison:
 AUNE X1 - left channel (blue) noticeably louder and notice the amplitude fluctuations over time.

Touch - Notice it's more noisy with unpredictable amplitude spikes occurring in both right & left channels.

TEAC UD-501 - more stable, clean, uniform waveforms in comparison.

As much as it's great to see the level of performance afforded by DACs these days, I'm very impressed by the level of performance of this old E-MU ADC! As I have stated before, one of the reasons I put up these posts is to demonstrate that it doesn't take megabuck equipment to test out audio gear objectively. A lot can be "known" about the performance of a piece of hardware rather than depending on only subjective "opinion".

The other test I would categorize as the equivalent of "pixel peeping" is the Dunn jitter test where we're "peeping" into a small part of the audio spectrum around the 11 or 12kHz primary signal and scanning for sideband anomalies. IMO, neither the jitter nor this undithered LSB test really are that important for audio quality. Random noise affecting the 16-bit least significant bit would sound like some form of dither (eg. like what happens when an HDCD with embedded LSB data is decoded by a non-HDCD player). Likewise, my feeling is that even a "moderate" amount of S/PDIF jitter (like say 1ns) isn't going to intrude into my listening pleasure. (Maybe one could make the argument that the details and nuance of sound/music can reside in these microscopic domains but I have yet to see any proof...)

Assuming the digital player/DAC is meant to be faithful to the source signal and doesn't implement a DSP known to affect the LSB data, to be able to measure and verify precision down to these levels I believe would be a reasonable pre-requisite in achieving high-fidelity. It's a test of how well the hardware was designed and implemented than necessarily how it "sounds". Just like knowing if a hi-res digital camera is capable of the resolution it claims... You might never need 36 megapixels for a slideshow or in print, but it's good to know that the camera was capable of delivering on the claims! Likewise, if I'm going to spend a good amount of money on high-fidelity gear, I'd certainly like to know that precision engineering went into it by the results of tests like this among others already discussed over these months.

Let's throw some nostalgia in. Here's what the MUSE Mini TDA1543 x4 NOS DAC looks like down at -90dB (using the CM6631A USB-to-S/PDIF coaxial interface):

Party like it's 1991! Ugly... Clearly it's incapable of accurately reproducing the 16-bit LSB undithered tone.

Zoomed out (24/44) - still ugly:

Using a 24-bit signal makes no difference since this is a 16-bit DAC and the lower 8 bits get truncated. The Philips TDA1543 DAC chip was introduced back in 1991 according to the specs sheet... Thankfully, it looks like DAC designs have improved somewhat since then at least in this characterstic :-).

A stroll down memory lane... The top 3 highest grossing movies of 1991: Terminator 2, Robin Hood: Prince of Thieves, Disney's Beauty And The Beast. Top 3 songs (Billboard): (Everything I Do) I Do It For You, I Wanna Sex You Up, Gonna Make You Sweat (Everybody Dance Now). Hmmm...  Good year :-).

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Folks, much of the measurements above were done about 3 weeks ago but I'm putting this post up behind the "Great Firewall" while on vacation (hey, >10hr plane flight gave me plenty of time to do some writing!). I know a few people are trying to get hold of me by E-mail. Unfortunately my VPN + Outlook is a bit finicky so other than more important work related matters as I check the E-mail every few days, I will likely not be responding until mid-August.

Time to go enjoy some good food... And snap some pictures of course... :-)


BTW: For those interested in some light non-fiction summer reading, consider picking up Chuck Klosterman's "I Wear The Black Hat: Grappling With Villains". An enjoyable, thought provoking social commentary.