MEASUREMENTS: TEAC UD-501 PCM Performance (Part 2) [Updated June 23, 2013]

Okay folks, let us continue with the TEAC evaluation... First, we need to look at the PCM performance of this DAC. Although DSD may be the "hot" feature of DAC's these days, PCM remains the most important digital encoding method. A good DAC MUST perform well with PCM music.

General setup:

MacBook Pro (Decibel bit-perfect) --> shielded USB --> TEAC UD-501 --> shielded 6' RCA --> E-MU 0404USB --> shielded USB --> Win8 laptop

The TEAC has quite a "hot" XLR output and unfortunately clips the E-MU so I was unable to get an accurate reading without using volume attenuation (rest assured it does look very good, dynamic range is probably about another 6dB better that what I got with the RCA 24-bit tests; beyond the resolution of the E-MU).

A look at a 24/44 1kHz square wave at 0dBFS using SHARP digital filter. RCA peak voltage at 2.8V. Nice wave morphology. Yellow is right channel, blue is left; channel balance looks good.

PCM 16/44:

The most common digital sampling rate is of course "good" old 16/44 Red Book format. These days, any DAC worth it's salt MUST perform close to ideal at 16/44...

Summary (RightMark 6.2.5):

As you can see, the UD-501 was measured with the 3 digital filters (DF's - OFF, SLOW, SHARP). Comparison was made with the Logitech Transporter (ethernet), Touch (ethernet), and Oppo BDP-105 Blu-Ray player (USB). Unless explicitly adjusted, vast majority of DAC's utilize some form of the SHARP filter by default at least for 16/44. Overall, you see that 16-bit audio is absolutely no problem for any of these devices.

Here's the frequency response of the devices:

The most obvious thing to see here is that the Touch rolls off on the low end by 1dB compared to the others, and the digital filter "OFF" setting of the UD-501 rolls off quite early starting around 5-6kHz...  Let us focus for a second just on the TEAC:

Interesting; the SLOW and SHARP settings are pretty self explanatory (the Transporter has similar settings). The OFF setting results in significant roll off even earlier and by about 18kHz, the OFF setting is about -2.4dB, compared to SLOW setting at -1.7dB, and SHARP at -0.1dB.

Hmmm, where have we seen that kind of filter "OFF" curve before? Oh yeah, the old TDA1543 :-). Here ya go:

What does this mean? Yup, the TEAC can function in "NOS [NonOverSampling] mode" with the digital interpolation filter turned off! Behold, stair-stepped NOS waveforms out of a modern DAC with DSD capabilities:

Digital filter OFF:

Digital filter SHARP:

That's really quite a trick from the TEAC!

Noise Level:

All pretty equivalent with fantastic level of functioning. Note the 60Hz powerline hum visible.

Stereo Crosstalk:

Very close; worst being the SB Touch. Same 6' shielded RCA cable used in all tests.

PCM 24/96:

24/96 is the "sweet spot" for high-resolution PCM DAC's these days. Certainly in DAC's I have previously tested, once you go above 24/96, there's often deterioration in the dynamic range. Furthermore, I do not believe there is any scientific evidence to suggest human ears can experience sound beyond the resolution encompassed by 24/96 so it's important that a true "high resolution" DAC be able to demonstrate adequate performance at this level.

Here's the "big board" summary with a number of devices tested (you probably need to click on the image for more comfortable reading):

As you can see, for comparison I've thrown in results from the E-MU 0404USB itself, Logitech Touch, ASUS Essence One, Logitech Transporter, and Oppo BDP-105. Obviously every one of these devices is capable of >16-bit resolution showing improved dynamic range beyond the 16-bit test above. "Top tier" devices are the TEAC, Transporter, Oppo; each measuring beyond 110dB potential dynamic range using the RCA output - essentially at the limit of the E-MU's abilities (the Essence One & E-MU would also be on this list when using balanced XLR or TRS cables respectively).

Frequency Response:

Since the graph got too busy, I removed the ASUS and Oppo - they basically look like the Transporter in terms of frequency response. Again, the Touch drops a dB down near 20kHz.

Here's the graph with just the TEAC settings plus the old TDA1543 NOS:

Notice again the similarity of the TEAC's digital filter "OFF" setting and the TDA1543 NOS DAC in the high-frequency end.

THD:

Interesting increase in high frequency noise with the digital filter "OFF". Looks like unfiltered delta-sigma noise shaping coming through?

PCM 24/192:

Next, one more step up in sampling rate:

For interest, I threw in the Logitech Touch with EDO plugin --> coaxial --> AUNE X1 DAC. Notice how well this combination measures! The AUNE X1 is only a $200 DAC and the combination produces very respectable measurements (and sound very good IMO). In comparison, I am disappointed in the Essence One going from 24/96 to 24/192. The TEAC and Oppo really hang in there with essentially identical results compared to 24/96 - great to see!

Frequency Response:

As I mentioned in the MUSE TDA1543 measurements, one way to improve NOS DAC performance is to feed it with higher sampling rate data...  In doing so, you get closer to the performance of oversampling interpolation filters. You see this here - the higher the sampling rate, the closer the digital filter "OFF" curve gets to the "SLOW" and "SHARP" settings (in fact, you see in the next section, they become identical).

There's that early roll off with the ASUS Essence One previously measured.

Noise Level:

Essence One getting a bit noisy at high sample rate compared to the others (realize it still has >100dB dynamic range though). Again, we see quite a bit of high frequency noise with the digital filter "OFF".

PCM 24/384 (more than DXD [352.8 kHz]!):

This is a "pseudo-test" actually. The fact is that the E-MU 0404USB is incapable of digitizing at 384kHz so what I did was upsample the 24/192 test signal using SoX so see if running the TEAC at the higher sampling rate will cause a measurable loss in the analogue output dynamic range or worsen noise characteristics within the measurable capability of the E-MU.

Summary:

First 3 columns were measurements done with the TEAC running at 24/384 with various digital filter settings. The last column is the "SHARP" filter measured at 192kHz. There may have been very subtle loss in dynamic range. Some or even all of this could be due to the upsampling conversion algorithm. In any case, the measurements look excellent and it seems indeed the TEAC is able to maintain low noise even at the extreme sampling rate of 24-bit & 384kHz!

Frequency Response:

Note how the NOS-like digital filter "OFF" setting is identical to the other settings now. Basically, sampling at 384kHz is like 8x oversampling of a 44kHz signal (2x oversampling of 192kHz).

Jitter:

As usual, let us look at some FFT's from the Dunn J-Test. For simplicity, I'll just show the spectra from the SHARP filter setting.

USB input (16-bit and 24-bit spectra):

Coaxial input using CM6631A USB to S/PDIF:

TosLink input using CM6631A USB to S/PDIF:

TosLink input again fed by CM6631A with *24/192 upsampling*:

The reason I didn't bother showing any results from hardware upsampling to 24/192 in the tables above was because the numbers and graphs looked essentially unchanged. However, there is one situation where upsampling makes sense... The same reason Benchmark chose to use ASRC (Asynchronous Sample Rate Conversion) for the DAC1 and DAC2 - jitter reduction. Although by no means high, the sidebands are more pronounced using coaxial and TosLink interfaces. The sideband peaks around the primary signal clearly were reduced with 24/192 upsampling using the TosLink input. As usual, whether anyone can actually hear this difference in properly controlled testing is another matter!

Summary of PCM Results:

TEAC has created a machine which objectively compares very well to some other excellently measuring devices like the Logitech Transporter and Oppo BDP-105. It's great to see that even operating at the extremely high DXD-level sampling rates, noise level remains low and dynamic rage appears preserved.

What I found surprising was the option to allow the digital filter to be turned "OFF"; I don't recall any reviewers spending much time on this (even the AudioStream review just glossed through this and didn't comment on the sound). This setting puts the DAC into a "NOS mode" where digital interpolation is suspended - this appears novel especially in a device with low-jitter asynchronous USB interface and a true 24-bit (err... ok, 32-bit as if that makes a difference) DAC... In general NOS DACs these days are still based on obsolete decades-old DAC chips like the Philips TDA154x (16-bit) or Analog Devices AD1865 (18-bit) which tend to perform poorly on measurements. Although personally I am not a big fan of the roll-off and aliasing distortion, some have commented on subjective improvement by taking out the digital oversampling filter, so I definitely consider it a positive that TEAC offers this option for anyone to try (in real time with instantaneous A-B'ing no less just by turning the knob)! I can certainly see this option useful to tone down some of the overly "bright" digititis-inducing recordings. Looking at my pop CD collection, an example where this was demonstrable was Jason Donovan's disco-inspired Too Many Broken Hearts from Ten Good Reasons (first pressing, 1989) where the OFF setting was more tolerable after 3 minutes :-). As a compromise, the SLOW filter may be reasonable.

As I mentioned at the beginning, PCM remains the cornerstone of digital audio. These TEAC UD-501 results suggest that nothing has been sacrificed in terms of performance in the PCM domain. Note that the ASUS Essence One is also based on the PCM1795 chip in dual-mono configuration but doesn't measure as well, highlighting the importance of the electronics around it like the analogue output stage, power supply and USB/coaxial/TosLink interface circuitry affecting the final output quality. One thing I wish the TEAC had from the ASUS is the beefier headphone amp though.

Bottom line: these results are consistent with the excellent subjective sound quality described in the previous UD-501 blog post. I would happily present some kind of award if it meant anything :-).

INITIAL IMPRESSIONS: TEAC UD-501 USB PCM & DSD DAC Reviewed (Part 1)

This guy arrived at my doorstep on May 7. Over the next week or so, I'll just build up this blog with TEAC UD-501 information as I gain experience with the unit.

Initial Impressions & The Basics:
By now, you would likely have seen the specifications sheet on this device if you've been researching.

It came relatively well packed in the box. I paid the current market price ~$850USD. Standard styrofoam protectors to withstand bumps and thick plastic bag around the unit itself. Inside the box is just a standard decent IEC power connector, an instruction pamphlet I didn't even look at and a really unimpressive thin zip-cord RCA cable :-).

The unit itself IMO looks great as do the line of "Reference Series" gear - utilitarian in terms of knob and display placement with a hint of the TEAC heritage with "pro" gear given the side metal handle bars - looks like rack-mount gear. Remember that TEAC [Tokyo Electro Acoustic Company] Audio is in the same family as Esoteric (consumer audiophile) and TASCAM (pro audio); depending on how you look at it, I guess it's either an upscale TASCAM without all the plastic or 'baby' Esoteric without as much of the mass and audiophile aesthetics.

The weight is quoted as 9lbs and it certainly feels substantial. It's about the size of an A4 (letter) sheet of paper (front "handles" poke a bit forward) and 3 inches high. The construction is metal all around with a nice brushed metal texture so there's no shiny bits - nice. Knobs feel very stable and responsive. The headphone knob on the right rotates smoothly and the MENU button feels authoritative when pressed (unlike the front buttons for the ASUS Essence One - just one of those subjective look-and-feel things which adds to a positive impression).

The organic electroluminescence (essentially OLED) display is easy to read, has 3 brightness settings and an "OFF" setting. I like the amber color which is non-distracting and I made sure I set the default to the dimmest setting. Great also that the amber LED for input selection isn't too bright and certainly less distracting than the Essence One's blue LEDs (not a big deal for me but I know many folks get bothered by this).

Other than to get more detailed descriptions of the menu options, the manual is quite unnecessary - it's really easy to operate... Basically push the MENU button to toggle between options, turn the left knob to change selections, that's really it. In looking over the menu selections, one cannot help but think that the TEAC engineers basically took the TI/Burr Brown PCM1795 DAC chip, looked at the datasheet - considered the undocumented modes, and created a machine that took advantage of everything this DAC chip can do! Here are the main options:

1. PCM Upconversion to 24/192 - presumably could help reduce jitter.

2. PCM1795 digital filters: SHARP, SLOW, and OFF - hadn't seen the OFF option before; an interesting mode which I believe was intended to allow the DAC chip to be mated to an external filter.

3. DSD Analogue FIR filters: FIR1 to FIR4 - I'll discuss more about this when I present the DSD measurements.

4. Analogue output: either RCA, XLR pin 2 hot, or pin 3 hot. Cannot output both RCA + XLR.

5. Simultaneous headphones + analogue line out: ON or OFF.

6. USB input power - powers off the USB port if another input being used - not sure the reason for this, actually, just power saving I guess?

7. Setting mode display: ON / OFF for the display to show if upconversion is happening, PCM / DSD, sampling rate... Very cool. I leave this ON.

8. LCD dimmer - 3 levels & OFF.

If you look at the PCM1795 datasheet, you see that it's documented to be a 32/192 part and can do DSD64 (2.8MHz) conversion. Perhaps a little known fact is that this DAC chip is capable of 32/384 PCM and DSD128 (5.6MHz) as "undocumented" features which the TEAC designers obviously capitalized on. Note that the ASUS Essence One also uses the PCM1795 and "symmetrically upsamples" to 24/352 or 24/384 depending on whether the input sampling rate is a multiple of 44kHz or 48kHz.

So far, the Windows driver 1.02 seems quite stable. No problems with ASIO PCM using foobar2000, and DoP bit-stream support through JRiver 18.0 works well for DSD. The current TEAC HR Player 1.0.0.4 (small basic music player, "portable" so no install) works to play back DSD and can stream using either DoP or "native" ASIO 2.1. If you have DST lossless compressed DSD audio, the TEAC player doesn't seem to handle these but they're fine with JRiver.

On the Mac side (MacBook Pro with Mountain Lion), it uses the standard USB Audio 2.0 driver so nothing to install. I have used both Decibel for PCM playback and the "alpha" JRiver 18.0 for Mac works essentially the same as the Windows version for DoP support.

Subjective Sound Quality:
So far most of my testing has been with the Sennheiser HD800 pictured above. I'm just going to put on my "subjective reviewer" hat for a moment...

The headphone amp sounds good. It's not powerful - rated at 100mW into 32 ohms but it drives the HD800 loud enough including some relatively soft classical test tracks I had. The amp could easily drive these headphones to ear-splitting levels with the usual commercial rock/pop/jazz/country tracks. The AKG Q701's are a bit more difficult to drive so I would avoid using these with softer classical selections with the TEAC. It's quite clear that the ASUS Essence One has a significantly more power headphone section in comparison. (Of course if you're a big time head-fi fan, TEAC would want to interest you in the HA-501 headphone amp.)

So far, I have no complaints of the sound. PCM performance is excellent. For example, a test track I often use to weed out poor systems is Tyler Bates' "To Victory" from the 300 (2007) soundtrack. It's recorded "hot" and dynamically compressed and the cacophony of sounds tends to get muddled very easily on a poor system. This track was reproduced excellently with this DAC (I also find the emotional response - that sense of dread - conveyed by this track a good personal gauge).

On the Kodo track "Niji No Nagori" off the Tsutsumi (2000) album, there's a nice build up of multi-layered drums, flute, vocals, culminating in a woman singing with clapping, percussion, and male backgrounds around 5:00. The drums sounded dynamic and "full". Bass went deep with the HD800; and thanks to the "speed" of these HD800's, it sounded precise. Again, excellent performance and I would certainly rate this DAC+headphone amp highly.

Currently, I don't have much DSD music collected yet but have ripped a number of my SACD's which I know are either DSD sourced or high-resolution analogue in origin - no PCM or worse Red Book-sourced DSD for me like in this review, thanks.

Albums heard or tracks sampled: old analogue sourced Nat King Cole's The Very Thought Of You (Analogue Productions 2010), Pink Floyd's The Dark Side Of The Moon (2003 remaster), Michael Jackson' Thriller (1999 remaster), Al Di Meola et al. Friday Night In San Francisco (1997 remaster), Miles Davis' Kind Of Blue (2007 Japanese SACD). They sound good overall...  Limitations of the analogue source quite evident with obvious limited noise floor on most of these. The 80's sound of Thriller is pretty dated but I think the SACD version is the best sounding 'pressing' I've come across...

Modern DSD sourced SACD's: Erich Kunzel's Tchaikovsky 1812 (Telarc 2001), John Hiatt's Master of Disaster (2005), Jorma Kaukonen's Blue Country Heart (2002), Rachel Podger's Bach Violin Concertos (2010), Stuttgarter Kammerorchester' Die Rohre (Tacet 2003). Nice, clean, great sense of space especially the Stuttgarter and Rachel Podger SACD's.

There's very little DSD128 content out there as far as I am aware...  However, I downloaded a few of the samples from 2L. They sound excellent but since they're sourced from DXD (24/352), I could also download those massive files (1GB for 10 minutes!) and play them PCM direct and be even "closer" to the performance :-). Seriously folks, I think this would be a real waste of disk space!

You may be asking - is there anything "special" about the sound of DSD - especially after I penned this piece on DSD? Well, honestly, it's hard to say... Really hard to do any kind of direct comparison since the foobar200 ABX tool doesn't work for this, and the switch from PCM to DSD results in a soft 'click' sound as well as a brief delay...  Furthermore, volume levels aren't exactly matched. All I can say is the music just sound good whichever format :-). I don't think DSD is "needed" for good sound, but it's nice to be able to play back the music in whatever the original format was without transcoding.

I'll be back this weekend with some PCM measurement results...

Links to the objective evaluations:

PCM Evaluation (Part 2)

DSD Performance (Part 3)

MEASUREMENTS: Power Cables for Low Power Audio.

We are told - "everything makes a difference!"

Expensive power cables are an example of taking this principle more than likely to the extreme - well into the territory of the neurotic obsessive-compulsive. Some audiophiles claim there are very significant differences to be found by replacing standard cables like the common IEC connector varieties between the mains and one's gear. DIY plans are available on the Internet, and of course many enterprising companies have produced all kinds of cables to satiate those "believers". Like other cable claims, it's difficult to determine what scientific / engineering theory could account for these beliefs. While there could be some justification to use of heavy duty power cables for high-powered amps with dedicated circuits for example (very rare for home audio), why would someone need fancy cables for devices like DAC's or CD players where internally the AC is converted to low voltage and current DC to power the electronics? Furthermore, we all know that the electricity supplying our gear is connected by hundreds of miles of plain old non-"audiophile approved" copper cables of various diameter and quality.

In order to look for tiny differences, I'm going to try using various power cords with the ASUS Essence One DAC (note that my DAC is slightly modded with all LM4562 op-amps)... Let's see if there are any differences looking at the analogue output and changes to the J-Test jitter spectrum.

First, as usual, I had a look into my closet of cables to see what I have. Here are today's selection:

Cable A:
No nonsense generic freebie 6' cable that came with my old Antec computer power supply. Has the brand name "LINETEK" stamped on the connector.

Cable B:
Notice the green dot on the plug. That means this is a higher quality "hospital grade" cable. Also 6', but it's about 25% thicker, and twice the weight of Cable A. Strain relief is fantastic. The metal wall plug prongs are more substantial and the ground prong is solid metal instead of hollow like for Cable A. Presumably the thicker diameter indicates better shielding. I know this particular brand of cable is being used in the local hospital's ICU department. If this cable fails during use, patients could die...

Cable C:
I looked around to see what was the absolute WORST power cable I could come up with. Here it is - total 56' long. Using Cable A, I connected it to a 50' yellow outdoors cable I used over the Christmas holidays for the outdoor lights. In fact, this cable has been used for this purpose for the last 5 Christmases at least, so it's been exposed to the dirt, rain and snow. The metal prongs in fact look worn and oxidized. In fact, this is so nasty that I took a picture of it out on the deck since my wife refused to have it indoors for more than a few minutes for testing :-). I tested it connected to the DAC pretty much looking like this tangled mess. Unless you think the last 6' of generic power cable can make a difference, the "performance" of this cable should unequivocally "sound"/perform terribly.

Gear Setup:
I used a variant of the usual testing setup:
Win 8 laptop --> shielded USB --> CM6631A asynchronous USB to SPDIF --> Acoustic Research 6' TosLink --> ASUS Essence One (*connected to wall outlet by test cable*) --> 6' XLR cables --> E-MU 0404USB --> shielded USB --> Win 8 laptop

Note that I decided to use the CM6631A device for USB input and TosLink out (previously tested) instead of the native Essence One USB because I actually found less jitter this way. I noticed that the Essence One's USB input has a fair amount of low level jitter artifacts - not sure if it's a result of the CM6631 (non-A) chipset or the drivers in this configuration.

Analogue Measurements (RightMark Audio Analyzer 6.2.5, 24/96):

Summary:

Pretty much identical...  Very small differences within the error range for each "run" of the test.

Frequency Response:

Noise floor:

THD:

Stereo Crosstalk:

As you can see, there's nothing here to differentiate the analogue measurements from the DAC using the different power cables.

Jitter Analysis (Dunn J-Test - 16-bit and 24-bit variants):

Cable A - 6' generic:

Cable B - 6' Hospital Grade:

Cable C - 56' - 50' outdoors corroded prongs + 6' Cable A:

Again - no real difference folks. Not really that one expects any difference since it's unlikely that the DAC's internal timing circuitry could be affected by the AC input. Note that with the Essence One, we can actually see the 24-big jitter modulation pattern due to the very low noise floor below -140dB.

Conclusion:

As usual, I listened to the audio output using the poorest cable configuration after I ran these tests and as I ponder what to write for the blog entry. Indeed, the sound was fine.

Tonight, I was listening to the Erich Kunzel & Cincinnati Pops' rendition of Tchaikovsky's 1812 Overture (Telarc 2001, SACD digitally ripped & converted to 24/88) with the Essence One powered by the nasty 56' length to the wall socket. It sounded good. By ~14 minutes into the track, we hear a multi-textured climax with church bells, choirs, brass, percussion and of course cannons. The complex mix was reproduced very well and rendered nicely with my AKG Q701 headphones - plenty of dynamics being pumped out into the Essence One's headphone amp.

Sure, it's possible that "everything makes a difference!" As in most things in life, the wise man needs to ponder the claims a little further to divine the truth. At least when it comes to power cables, I think the wise man can comfortably walk away from such claims of audible differences and realize that a decent IEC cable is all that's needed - at least for low power devices like a DAC.

As is my usual policy, I do not bother measuring high-priced cables - partly because I don't have any at home - but these posts are not about pointing fingers at specific companies. Rather I hope the measurements and comments stimulate thought. Note that I have "heard" expensive power cables over the years so am well aware of their "performance". As usual, drop me a note if you have good evidence to show otherwise...

MUSINGS: "Audiophile" Digital Cables... [Updated November 2013]

As I noted previously, the purpose of going digital has to do with prevention of signal corruption. In doing so,  we can speak of "bit-perfect" transmission of audio data in a way which is impossible in the analogue realm. For example, if we think about the main "container" of consumer high quality analogue music today - the LP / vinyl - nothing can be considered 'perfect'. Each LP is slightly different in terms of being free from warping or (hopefully) minor groove imperfections from the moment it leaves the pressing plant (even the quality of each stamper used varies by generation and age), each time the LP is played, a little bit of damage happens to it so every playback will be different. Even if you keep it in pristine condition, the ravages of time and environmental factors will take its toll on the material itself in large or small ways. Furthermore, there is no way to replicate the music in 'perfect' form as a result (unless you digitize it of course; but only to the quality of the LP playback gear and ADC).

As we know, the CD technology (~30 years old now!) is different. Small imperfections in the plastic or aluminum 'pits' do not lead to audible anomalies thanks to the Reed-Solomon error correction of the digital data. Furthermore "bit-perfect" ripping is routinely done (obviously to the horror of the music industry over the last few decades) and the result is literally innumerably perfect copies.

Let us turn our attention to "digital cables". For some reason, some people seem to forget the above and believe that different digital cables make a difference to sound even when there is no disagreement that bit-perfect data is being transmitted down the pipe in digital form. In fact, there has never been a plausible explanation provided by the supporters of different digital cables. Some talk of jitter being inherently different between cables, some that perhaps electrical noise will disrupt the phase transitions in a digital signal to worsen this jitter and perhaps degrade the bits. But where is the evidence for such beliefs beyond subjective "impressions"?

An industry has developed around digital cables of all sorts. Some of these cables are extremely expensive with price tags of hundreds to thousands. Purported benefits include more exotic / precious conductors, various types of insulation, winding techniques, upgraded connectors. While this is well and good - nobody denies that a well built USB cable with excellent strain relief and connectors that do not break or oxidize is undesirable - why is it that so often audio quality gets thrown into this mix of features during discussions as if it's some kind of 'given'? If a friend says he/she bought a $150 cable that was well shielded, had great connectors, was the right length, and had great cosmetics, I do not believe I would question the motivations since these are all quite reasonable. But if they said "this $150 cable sounds better than all my less expensive ones", I think it would be reasonable to at least wonder about the truth of such a statement just as much as if the friend said "water tastes better from my wine glass compared to just a regular glass cup". Has there EVER been a proven example of a properly functioning digital cable sounding different from another item of the same type?

When it comes to cabling in general, I find it interesting that talk of sound quality is usually propagated by the audiophile press and audio reviewers on-line rather than directly from the manufacturers (see the addendum below for an example of a cable ad). False advertising is a legal offense after all while reviewers spouting off their opinion is given artistic license as subjective experience. This is all fine I suppose so long as it's "above board", but in a small industry where ad revenue is of major importance in the print magazines and web sites, do we really think there is a significant firewall between the reviewers and the source of financial support? A reminder - cables are one of the highest marked up items for any manufacturer. I wonder just what percentage of a cable manufacturer's budget goes into R&D vs. advertising...

Turning to more "objective" matters, let us recap. Over the last few weeks, I measured a number of digital cables of various types in my standard test setup:

USB cables:
http://archimago.blogspot.ca/2013/04/measurements-usb-cables-for-dacs.html
S/PDIF Coaxial cables:
http://archimago.blogspot.ca/2013/04/guest-review-measurements-dr-franks.html
S/PDIF TosLink cables:
http://archimago.blogspot.ca/2013/05/measurements-toslink-optical-audio.html
HDMI cables (updated November 9, 2013):
http://archimago.blogspot.ca/2013/11/guest-review-measurements-quantum-hdmi.html

In each case, using what I had, I tried to "create" improbable setups (eg. very long cables, use of couplers and extenders) which serious audiophiles would likely feel will deteriorate the signal quality. Yet in NONE of these situations was I able to detect an actual loss of fidelity running test signals which have been successful in detecting various types of anomalies over the course of my postings. Subjective listening likewise did not suggest to me any deterioration in sound quality. In contrast, RCA analogue interconnect measurements can be shown to have subtle differences even with relatively short lengths.

What else is there to say, really? In my opinion, there is no other way to interpret the data than to conclude that digital cables of adequate quality to transmit the data in a bit-perfect fashion makes no difference to sound quality. Furthermore, there is no evidence to suggest that the cables influence jitter to any significantly audible degree (again, "jitter" tends to be the scapegoat for almost all digital imperfections for selling hardware). Yes folks, bits are bits as far as the digital cable is concerned. They were engineered to be like this. Over the years I have tried my hand at listening tests with digital cables; but never once have I been able to convincingly differentiate cable quality in any blind testing.

Of course, I could be wrong and open to this possibility...  As usual, if you have good data to show differences between "working" digital cables, please leave a comment.

Enjoy the music...

Addendum:
Here's an interesting advertisement showing "proof" of something (I reproduce this as 'fair use' for the purpose of commentary with no expectation of benefit to myself financial or otherwise):

For the purpose of discussion around just the contents of this ad, I blurred out the company information and trademarked names...  You're welcome to check out the ad found on page 45 of the January 2012 issue of The Absolute Sound (same issue as one of the most disinformative series of articles about computer audio ever to 'grace' an audio magazine from "Dr. Charles Zeilig and Jay Clawson").

1. These cables meet or exceed $20K-$60K competitors' performance. What length are these $20K-$60K cables??? What cables cost this much? Are we talking individual cables or cabling a whole studio? All I can say is throwing a huge number out like that could be either "impressive" or absolutely ridiculous.

2. What is this "patent-pending" XXX Technology? Is it metallurgical? Connector +/- plating? Cable topology? Insulation material? Such a mystery! (To be fair, you can read more about it on the web page to some degree and ponder the claims - go see the ad.)

3. "Nice" plots of square waves I guess...  So it's "absolute proof" that XXX Technology improve rise and fall times of a square wave. We know nothing of the length, type of wire, or even what changed between the "conventional cable" compared to the "same cable" with XXX Technology. Yeah... Nice and "scientific" looking but totally lacking in transparency!

4. What does that square wave plot mean for audio, exactly? Are they trying to say these are digital cables where more precise square wave transitions might imply less timing inaccuracies? But we see analogue speaker spades and XLR connectors (I suppose could be AES/EBU).

5. Notice there's no claims of sound quality. Even the TAS and Rick Rubin quotes say nothing about sound quality, rather something nebulous like "performance". Interesting, given that TAS reviewers commonly speak of comparative sound quality in their reviews of cables yet the company chose not to include such quotes, why?

6. Notice the nice arrows showing directionality of cabling for the speaker spades...  How thoughtful.

Things that make you go... Hmmmmm...

MEASUREMENTS: Analogue RCA Interconnects.

Now that I've measured the main digital cables used for audiophile listening these days (USB, coaxial, TosLink), I figure it's time to demonstrate what happens when we bring the testing methodology with analogue cables. [I'm hoping in time HDMI will make some headway into the audiophile DAC world since I look forward to multichannel playback one day through my computer server.]

Remember why we got digital in the first place: robust data storage free from transmission and generational losses - in other words, resistance from corruption.  By transforming data into 1's and 0's, we quantize the data into binary form and complexity is thus encoded in larger quantities and combinations of this quantized binary data which can be saved in a form which makes detection and correction of error possible.

As a result, when digital 'works', it likewise tends to be 'all or nothing'. What we saw with the digital cables is an example of this. Despite some really poor quality cables tested (the Dr. Frankenstein models!), the measurements were essentially identical in each case (they all worked). Parameters like impedance and capacitance of the cable do not affect the transfer of data unless of course they are outside of tolerance for the interface. It's of course possible that the occasional 'bit' of error occurred with poor cables, but obviously it was not large enough to encroach on the measurement results (nor affect the subjective audibility when I was listening). Beyond "bits are bits", in the timing domain, there have been reports of very long cable lengths potentially worsening timing of the digital signal (ie. jitter), what I have seen suggest lengths of 20-30m AES/EBU adding maybe 20ps - totally irrelevant to audio performance and at lengths we generally do not use in the consumer setting.

Let's see now how good ol' analogue interconnects of various lengths fare.

Here are the models being tested:

Cable A:
3' freebie RCA cable that came with an old cheap DVD that has since broken. Connectors not gold plated.

Cable B:
3' Radio Shack shielded RCA cable. Gold plated connectors.

Cable C:
6' Radio Shack shielded RCA cable. Gold plated connectors.

Cable D:
10' poorly shielded composite cable (with stereo audio). Gold plated connectors.

Cable E:
3' pure 4N silver, 4-core braided interconnect. Connectors are gold plated Neutriks. Soldered with Cardas Quad eutectic silver solder. Got this cable about 2 years back and used for my SACD player from here.

Cable F:
With apologies to Keaton & Minoeall-san, I used the 'Super Connectors' from the "Best-Coaxial-Digital" cable along with the two lengths of 10' composite cable and 6' stereo RCA and created an un-audiophile-approved 16 foot RCA "double cable" interconnect.

Setup:
Win8 laptop --> shielded USB --> CM6631A async USB to SPDIF --> 3' coaxial --> AUNE X1 DAC --> *test analogue interconnect* --> E-MU 0404USB --> shielded USB --> Win8 laptop

Summary RightMark 6.2.5 results (24/96):

Frequency Response:

Noise Level:

THD:

Stereo Crosstalk:

Summary:
1. Analogue ain't digital! Although in most ways the measurements are very similar (these are short lengths of interconnects after all), mild differences can be found.

2. Frequency response unchanged among the cables. Interesting. Some people talk about analogue cables as "tone control". I don't see it using these interconnects even with longer length (there is a hint of high frequency roll-off with the 16' cable but really this is trivial) or different conductor material. Using silver interconnects, there are no changes in the frequency response to suggest these cables sound "brighter" as some contend :-).

3. Interesting Stereo Crosstalk performance. Stereo crosstalk looks to be sensitive to cable length. The silver cable had the least crosstalk up to 5kHz and then increased from there - this is possibly a function of the fact that it's constructed as 2 separate cables as pictured above rather than the zip-cord arrangement of the other cables.

4. Measures like THD should not (and in fact does not) show a difference. After all, cables are passive "components" so should not introduce harmonics into the equation. As for noise floor, I suspect if I were to test under conditions with strong RF noise the poorly shielded cables would perform worse (may try this later), but in the home environment where I tested, obviously this was not a problem even in reasonably close proximity to the laptop, DAC, and E-MU ADC.

There you go. Analogue interconnects do make a slight difference and this is quite measurable particularly in terms of stereo crosstalk performance. Remember that these interconnects are of relatively short lengths so minor differences are really not surprising. The obvious question is - would humans be able to differentiate these interconnect cables based on listening tests? I honestly doubt it. Subjective listening using my test setup did not reveal any noticeable change with the long cable vs. the short silver cable. Realize that even with the long 16' cable, stereo crosstalk was still below -75dB which should be inaudible - for comparison, high-end LP cartridges are only capable of 30-40dB crosstalk performance.

Musical selection tonight was Rachel Podger & Brecon Baroque's renditions of Bach's Violin Concertos on Channel Classics (SACD converted to 24/88). Sounds great with the 16' Frankenstein cable with my Sennheiser HD800 headphones off the E-MU 0404USB.

MEASUREMENTS: TosLink digital optical audio cables.

Let us now finish off testing the digital audio cables at my disposal. Already we're seen that USB and coaxial SPDIF cables did not have any measurable differences even with poor construction and length. Remember that the benefits of TosLink ("Toshiba Link") is that they are non-electrical so have the benefits of being resistant to electrical interference. Furthermore, it has been said that they can be used in long runs without loss (specifications allow up to 33 feet).

I have a few old TosLink cables hanging around of varying qualities and build. Let's have a peek in the closet:

Cable A:
This is the cheapest cable I have. I believe it was a freebie from one of my old DVD players. The only marking is along the side of the cable it says "VITOnet". Length 6' and relatively thin.

Cable B:
A small step up from the freebie. Branded "Thunder Cable" TosLink I got as a package with some other home theater cables I bought maybe 10 years ago from Costco locally. Again 6' and thickness of the cable about the same as the VITOnet, so it feels quite fragile in the hand.

Cable C:
Another step up in construction and price. A 6' Acoustic Research Pro TosLink cable. Nice gold plated connector now with good strain relief and quite a thick caliber. Maybe about $20 when I bought it. Has served me well for years between the DVD player and a Denon receiver.

Cable D:

Up to this point, all the cables have been plastic optical fiber. This next one is of glass cable construction. Can be purchased off Amazon here for ~$20. Construction is also very good with nice metal connectors, gold plated terminals, and good cable thickness. According to the "specs", the cable supposedly has "280 individual stands of glass". Again, the length is the same at 6'. Note that it's not necessarily a given that glass is superior to plastic; for LED light sources, it has been said that plastic cables might even be better.

Cable E:

The "worst" Dr. Frankenstein cable I could construct from what I had was with the use of a $3 TosLink coupler off eBay. This adds an extra transmission interface and of course extends the length of the cable which could worsen signal integrity. I coupled the 2 cheapest TosLink cables I described above - the VITOnet (Cable A) and Thunder Cable (Cable B) - for a total length of 12'. I tested the cable looking just like this with it coiled up.

Analogue Tests (RightMark, 24/96):

Standard methodology:

Win8 laptop --> 6' shielded USB cable --> CM6631A asynchronous USB-to-SPDIF --> *test TosLink cable* --> AUNE X1 DAC TosLink input --> shielded RCA --> E-MU 0404USB --> Win8 laptop

Okay folks, here's the summary...

I think as you can see from this table, the test results are essentially exactly the same. 'Cable E' was measured about 2 weeks after all the others (I was waiting for the coupler to arrive from Asia); notice how reproducible the test results are.

Frequency Response:

Noise Level:

THD:

Stereo Crosstalk:

No difference.

Jitter Analysis (Dunn J-Test Signal 16-bit & 24-bit):

Cable A (6' VITOnet):

Cable B (6' Thunder Cable):

Cable C (6' Acoustic Research):

Cable D (6' Glass):

Cable E (12' Coupled VITOnet + Thunder Cable):

For the 12' Cable E, I even started waving the cable around at the coupler joint to see what would happen to the jitter spectrum... Nothing of significance!

Notice that the CM6631A USB-to-SPDIF converter has quite low jitter overall despite this being TosLink - few nasty sidebands and little spectral spreading of the primary signal (usually in my other measurements TosLink not as good as the coaxial interface).

Conclusion:

TosLink cables measure the same based on these results. Inexpensive 6' plastic, better quality plastic, glass, or a longer stretch of 2x6' cable with a coupler did not show any measurable difference in the analogue output from the AUNE X1 DAC used to test. Likewise, jitter analysis with the Dunn J-Test in both 16 and 24-bit versions did not demonstrate any appreciable difference between the cables. As far as I can tell, jitter does NOT appear to be affected by the TosLink cable quality based on these tests.

Subjective listening to the 12' coupled Cable E likewise did not show any musical anomaly - was able to enjoy Jorma Kaukonen's Blue Country Heart thoroughly through the AKG Q701's :-).

I think this concludes my survey of digital cables - at least for now...