Hi-Res THD(+N) vs. Output Level Measurements (ESS "HyperStream" vs. AKM vs. TI/Burr-Brown). And a bonus R-2R!

Notice last time as I ended off the post, I showed what I think is an interesting "high resolution" graph of THD(+N) vs. Output Level for the Topping D10 Balanced which uses the ESS ES9038Q2M chip. This was spurred on after some discussions on glitches and anomalies one might see due to the "HyperStream" architecture of the ESS chip.

These days, other than the occasional fully multibit or discrete R-2R DACs, the vast majority of what we're using are multibit/multilevel sigma-delta devices. This includes the brands I have listed in the upper graphic; Asahi Kasei Microdevices (AKM), ESS Technology, and Burr-Brown (which was acquired by Texas Instruments in 2000). We'll also talk about the Philips later. ;-)

Today, let's have a look at "high res" THD(+N) vs. Output graphs (XLR output where possible to keep noise as low as possible) comparing different DACs from these companies...

ESS Technologies:

Let's start with some DACs based on ESS' converter technology with their "HyperStream" modulator.

Here is what I published last time (with slight adjustment to distortion units) of the Topping D10 Balanced (ES9038Q2M), examining -25dBFS to 0dBFS using REW's "stepped sine" measurement system at increments of 0.1dB:

Measured values in the legend correspond to 0dBFS.

Below -25dBFS, most high quality DACs will have harmonic distortion low enough to be buried in the noise floor so the pattern isn't as noticeable or interesting. As you can see, we have quite a patterned level of harmonic distortions especially the odd-order 3rd, 5th, 7th, and 9th showing a sinusoidal pattern which gets more compressed closer to 0dBFS. If we were to watch the harmonic distortions in realtime, we would see an undulating increase and decrease in the odd harmonics as output level changes while the even harmonics follow a less predictable pattern at lower levels.

Let's have a look at another ES9038Q2M device to double check - here's the S.M.S.L. DO100 I reviewed recently:

Values in the legend correspond to 0dBFS.

Again, we're seeing a similar pattern. While overall the noise level and THD+N are better at 0dBFS, we're seeing that sinusoidal pattern of odd-order harmonics play out into 0dBFS. As with the Topping D10B, the 3rd harmonic tends to be the strongest with significantly lower 2nd harmonic.

Hmmm, how about a device using the ES9038PRO chip? Here's my Oppo UDP-205:

The Oppo UDP-205, while discontinued since 2018 remains a "beast" of a 4K Ultra-Blu-Ray, SACD, and pretty well everything else including full MQA decoding player (the main exception being HDCD). It has two ES9038Pro chips inside, one for the stereo output, the other for multichannel. Since I have not measured this device for years, I thought it would be fun to have a look at the 1kHz THD+N using the E1DA Cosmos APU + ADC setup first:

THD+N about -119dB - very good. Notice that we see a number of side-bands around the 1kHz signal which are likely power-supply related as they are even multiples of 60Hz, the mains hum frequency here in Canada.

So, what about that hi-res THD(+N) vs. Output Level graph?

Values in the legend correspond to 0dBFS.

Yup, like the ES9038Q2M devices above, the ES9038PRO also has a pattern of fluctuating odd-order harmonics when examined in detail although in the Oppo design, perhaps not as clearly defined below -15dBFS.

Let's look at an ESS chip that's a step down from the ES9038 line, using an earlier version of the "HyperStream" ("HyperStream I" as it were). Here's the S.M.S.L. M100 Mk II powered internally by the ES9018Q2C previously reviewed:

Still one of the cutest looking DACs I think!

While the noise level is higher (to be expected with RCA output), the 2nd harmonic rises substantially with increasing output level, and THD+N is not great at -92dB at 0dBFS, underneath all that, we also see a similar pattern of regular odd-order harmonic rippling with the ES9018's HyperStream I.

Let's now have a look at devices not using the ESS DAC chips...

Asahi Kasei Microdevices (AKM):

Until the AKM factory fire in October 2020, these DAC chips were very popular among hi-fi devices. So while there appears to be some good news on the factory repairs, AKM-based DACs probably will still remain rare or in limited supply through 2022. It is nice to see the recent announcement for the AK4493S and AK4499EX/4191EQ though.

I have a couple of RME devices here to look at based on AKM's 256x oversampling, internal switched capacitor filter, and "OSR Doubler" SDM architecture.

The RME ADI-2 Pro FS R Black Edition is based on the AK4493 "Velvet Sound" chip:

Values in the legend correspond to 0dBFS.

Notice the significant difference compared to the ESS Tech DACs. The AKM DAC has a much more predictable pattern of harmonic distortion with the 2nd order predominating until right around -3dBFS after which the 3rd becomes the highest. Higher order harmonics are nicely suppressed throughout.

Let's double check then with another product. Here is the dual AK4493 Topping DX3 Pro V2 previously examined (note that this is not the current Topping DX3 Pro+ which has switched over to the ES9038Q2M):

While distortion amounts are different from the RME above, and noise overall higher than XLR output, we're still seeing a relatively smooth harmonic pattern across the output levels.

Let's look now at the lower model AK4490 "Verita" chip which is found in the older RME ADI-2 Pro FS:

Values in the legend correspond to 0dBFS.

Very nice -110dB THD+N (XLR out). The "family resemblance" with the newer RME ADI-2 Pro FS R BE is clear with 2nd order predominating until just below -2dBFS then the 3rd harmonic rises above.

Overall, the more predictable "cascade" of harmonics with generally decreased higher order amounts in the AKM I think in principle is very nice; probably more "ideal".

TI / Burr-Brown:

Up next, let's have a look at the TEAC UD-501 again with its "Advanced Segment" (hybrid: likely upper 6 bits multibit and lower bits 3rd-order SDM) TI/BB PCM1795 DAC chip inside:

Values in the legend correspond to 0dBFS.

Like the AKM DACs, this is also a smoother pattern than the ESS. Also like the AKM, depending on the output level, 2nd and 3rd harmonics predominate with a transition taking place around -7.5dBFS with the 3rd harmonic dropping below the 2nd. Higher order harmonics are generally well suppressed.

BONUS! Philips TDA1543 x 4 R-2R NOS DAC:

Okay, thought I'd throw in a bonus "vintage" DAC here for fun ;-).

That's my old "MUSE" Philips TDA1543-based DAC with 4 chips running parallel which I've used over the years to discuss NOS and by extension, R-2R ladder DACs (BTW, nice concise review article on the technical aspects here). I believe there are still DACs in the audiophile world sold based on these old Philips TDA1543 chips which were first released around 1989.

Quite expensive models like this CAD DAC are sold these days using increasing numbers of 8 and 16-chip configurations. Compared to the modern multi-bit SDM technology, the TDA1543 cannot truly be called "high-resolution" or "high-fidelity" depending of course on one's definition of "fidelity" regardless of the hype a company might use. Unless a listener is trained, there is not necessarily close correlation between the fidelity of a device and the subjective "euphonic" quality based on individual preferences.

For my testing, here's what the set-up looks like using the E1DA Cosmos APU and ADC:

Depending on test, source can be the Raspberry Pi or directly from the computer when doing REW stepped sine.

Since this is a purely S/PDIF-input device, I'll using the Topping D10s as a USB → TosLink S/PDIF converter to feed the DAC (optical galvanic isolation). While it's limited to 16-bit conversion, the DAC can accept 96kHz samplerate without complaint (up to 192kHz coaxial I believe). Notice that I'm using a 12V/6A lithium battery pack which is as noise-free as it gets. A good quality glass TosLink cable in the set-up.

Here's the 0dBFS 1kHz 24/96 pure sine wave FFT to give you an idea of the resolution:

That's obviously not very good with THD+N -64dB ("only" 0.06%) at 0dBFS for a DAC. More fancy designs like those 8/16-chip configurations should be able to improve on the noise level to some extent (it better if it costs more than US$50, the approximate price of this old DAC!).

This is a NOS DAC with stair-stepped, squarish waveforms - here's a zoomed-in look at the 1kHz output at -25dBFS:

Those sharp waveforms will show up as excess odd-order harmonics in the FFT. We can see this when we look at that -25dBFS 1kHz tone above:

While noise higher, notice that the -25dBFS 1kHz sine signal actually has better THD+N of around -70dB compared to 0dBFS thanks to much lower overall harmonic levels, especially the 2nd.

While there's still a fair amount of 2nd harmonic, it's obvious the odd-order distortions predominate well beyond the highlighted 9th harmonic label. Folks who express a preference for pure NOS playback of 16/44.1 material - often they will say it sounds more "real", or more "spacious" - presumably like the effect of these odd-order harmonics (and -3dB roll-off around 20kHz).

Since I noticed quite a bit of distortion even at lower levels, here's the "hi-res" THD(+N) vs. Output Level graph from 0dBFS down to -50dBFS (0.2dB steps):

Measured values in the legend correspond to 0dBFS.

While not particularly pretty, this again doesn't have the ESS DAC's sinusoidal pattern of harmonics. You will notice some interesting trends in the distortion data.

* Odd harmonics are higher across the output levels creating the NOS "stair-stepped" morphology. Notice the very significant dissociation between the amount of odd harmonics congregating higher in level and the even harmonics lower (except for the 2nd).

* The 2nd harmonic cuts through the graph and rises persistently from -32dBFS to become the leading amount by about -9dBFS and above.

* Since each bit represents approximately 6dB of output, notice that we see discontinuities in the distortion presumably corresponding with each level of the R-2R ladder as it transitions along the network. For example, in the THD+N tracing, we see this clearly at -12/-18/-24dBFS. With the eye of faith, we can also see smaller irregularities at -30/-36dBFS as well. Distortion levels are already quite high at -6dBFS so anomalies there would be hard to see. Precision of the current source and resistor values are essential for high-resolution performance and even slight imperfections could lead to such irregularities in R-2R DACs; achieving such precision can of course be very expensive. (The goals of technological advancement with modern SDM DACs include better performance and much lower price.)

I think it's interesting looking at old technology like this and comparing it with how things have improved with modern DACs. While the MUSE TDA1543 is inexpensive, I'd be curious how higher-end devices with improved power supplies (note that I'm already running this on battery power) perform based on these old Philips chips. Anyone seen a measurement for the CAD TDA1543 Mk II for example? Regardless of expense, the limitations of the 16-bit TDA1543 I think are clear and there's something to be said about not throwing money into improving something that wasn't great to begin with. Claims about the TDA1543 providing some kind of "natural" sound as if these decades-old budget NOS parts were ever all that great is a bit strange to me.

Speaking of R-2R, recently we also saw how poorly the Cayin RU6 R-2R DAC performed whether in NOS or OS mode.

Summary:

A fistful of DACs!

I think it's quite clear comparing the DACs that the ESS chips' THD(+N) vs. Output distortion pattern is not like the others (although the Philips TDA1543 has its own character as well).

ESS "HyperStream" modulator-based DACs tend to capture a lot of the spotlight as they can achieve high numbers when we look at single measurements like 0dBFS 1kHz THD+N/SINAD. However, over the years, audiophiles have reported measurable anomalies like the "hump" and low-level noise floor "needles" in certain test signals at various amplitudes on the FFT. This variability in low-level harmonic distortion such as the FFT pattern at -2.9dBFS I used for the DSD 1kHz signal can look quite different from typical 0dBFS measurements.

While these anomalies appear to be very low level, the AKM graphs do look more "natural" at least in that given the choice, I would probably want to see uniformly invariant low distortion from a DAC. As with objective testing in general, the only way to truly judge whether something is audible is with actual blinded listening tests; as you're likely aware, these are very hard to come by in the audiophile hobby and that not everyone accepts blinding being important is IMO a problem. In ESS' 2011 presentation on the HyperStream at RMAF (here's the video), Martin Mallison suggest that "when the final artifact is removed, the listener starts to choose the HyperStream modulator (in blind tests) as being better than the conventional DAC" (~32:15 in the video). In 2011, the highest model product was the ES9018. This then suggests that the fluctuating harmonics are inaudible with trained listeners; regardless, it would certainly be interesting to see the results from such blind listening tests and how they were performed (I'm always curious what music was used).

Recently, ESS has announced the forthcoming ES9039PRO which promises better performance although the specs are not that different from the ES9038PRO: 8 channels, up to 132dB dynamic range per channel, and THD+N -122dB mono (same as ES9038PRO). It is said to use a "quad modulator" however, and they call it the "HyperStream IV".

While these specs numbers are impressive, I don't think it's reasonable to suggest or expect that this new DAC would sound much different from the current ES9038 models (with my belief that decent DACs these days are "perceptibly perfect" and all...). However, I wonder if objectively we'll see less harmonic fluctuations in the new chip when put on the test bench. Should be an interesting fight between the new HyperStream IV and AKM's upcoming Velvet Sound/Verita products.

[Yeah, I know there's also the ES9039MPRO. This is the version of the chip with embedded MQA "rendering" (as discussed here with the poor filters). Seriously audiophiles, enough with wasting time and money on this stuff, with basically only TIDAL HiFi+ tier content available. I don't think it's unreasonable of me to call this scheme literally stupid in 2022 and represents a downgrade in performance. IMO, avoid DACs using this chip to speed up the demise of the MQA nonsense and send a message to ESS and companies that still support it to not waste their R&D resources. Vote with your dollars.]

Finally, just a word about how some companies and reviewers keep telling us that "it's not the DAC chip... it's the analogue output circuits, etc... that determine the sound", usually with the intent of differentiating the "house" sound of the companies suggesting one brand might be significantly better than another (I've seen some companies hide the identity of the DAC chip used). Yes, of course that's true in that if the digital interface, or clocking, or power supply, or analogue output stages of the DAC are poor, then there will be sonic compromises. However, do realize that it is the DAC chip (or discrete circuit as the case may be) that is determining the ultimate potential resolution for the conversion. I think it is only reasonable to expect that reputable companies would want to achieve the highest fidelity from the converter chip so the final goal would be similar. No matter how excellent the analogue circuitry might be, how precise the clocking mechanism, the intrinsic properties of the DAC are what they are. As per the ESS graphs above, Topping, S.M.S.L., and Oppo all share in the fundamental property of ESS' HyperStream.

There are many analogies we can draw between DACs and computer components like CPUs these days. When you're sitting in front of a Windows machine working with a moderate to heavy load, you should be able to tell the difference in speed between an i3 and an i7 CPU. So long as the computer manufacturer allows the CPU potential to shine, do we attribute the expected speed mainly to the manufacturer like Dell, Lenovo, or ASUS, or do we recognize that it's mostly Intel's specific CPU model that provided the level of performance? So long as Dell, Lenovo and ASUS' supporting motherboard and components do not hamper the potential speed of the CPU (eg. slow RAM, buggy firmware, unreliable hardware), then in principle, the i3 or i7 will perform very similarly across brands. So too with modern DACs based on high-performance conversion chips; there is a potential level of fidelity which the chip is capable of and manufacturers can optimize that core potential, ensuring reliability, and perhaps adding useful functionality. Devices IMO will sound similar in most regards; and if they don't, we would almost certainly be able to measure the difference these days! ;-)

A fancy brand name can certainly get you the non-utilitarian rewards of a luxury product; just remember to not confound those putative benefits with playback fidelity by simply, truly closing our eyes when listening, dear audiophiles. ;-)

Okay ladies and gents, hope you're all enjoying the music! Happy Canada Day to the Canucks, and a great 4th of July to my American neighbours.

It's summertime in the north... Enjoy!