MUSINGS: Raspberry Pi 3 B+ "Touch" Optimizations; CRAAP Settings, and the "Extremus" Filter Setting.

Okay, let's have some fun with the Raspberry Pi 3 B+ motherboard, piCorePlayer, and my little "Touch" device I recently updated. As discussed before and in the picture shown above, these days, I have the inexpensive JustBoom Digi HAT (~US$40) board attached out the back for simple S/PDIF connectivity as well as USB when I need.

Today, let's hit a few topics related to the Pi 3 B+ setup above. Some little tweaks, things to get it working well, and fooling around with a piCorePlayer/SoX filter you can try for yourself without unnecessary hype nor expense...

MUSINGS: On the RMAF 2018 MQA talk, pseudonyms, and the right to anonymity.

“A desire for privacy does not imply shameful secrets; Moglen argues, again and again, that without anonymity in discourse, free speech is impossible, and hence also democracy. The right to speak the truth to power does not shield the speaker from the consequences of doing so; only comparable power or anonymity can do that.”

--- Nick Harkaway, The Blind Giant

Boo!

Well, Halloween's coming up and it looks like we're about to talk about some scary, dramatic stuff involving emotional incontinence and anonymity :-).

MEASUREMENTS: RME ADI-2 Pro FS as DAC (Part II - frequency response, noise, distortion and jitter)

As we saw previously, the RME ADI-2 Pro FS is based on the AKM AK4490 DAC chip and provides a good assortment of features like filter settings. We've seen that the headphone output amplifier provides plenty of power and the beginnings of what looks like a highly accurate DAC; consistent with my subjective opinion.

Time for part 2 of the objective evaluation today as we continue to explore the DAC output quality.

MUSINGS / MEASUREMENTS: A look at Intersample Peaks and Overload Tolerance... (RME ADI-2 Pro FS, TEAC UD-501, Oppo UDP-205)

I suspect that many audiophiles were introduced to the topic of intersample peaks (ISP) when Benchmark first released their DAC2 HGC which advertised and discussed the provision of +3.5dB overhead for digital conversion back in late 2012. Over the years they've discussed this in their blog such as this post that came out to discuss the technical bits of the Sabre DAC and DAC2 in particular.

Remember however that ISPs and the potential for intersample overloading have been discussed in the technical literature for years. For a good review of the topic, have a look at this paper from Nielsen and Lund "Overload in Signal Conversion" presented at the AES Conference in 2003. Because almost all modern DACs utilize oversampling filters, the internal interpolation creates extra "points" between samples. For loud music (common since the late 1990's!) with samples approaching the 0dBFS level if not already clipping, it's likely that many of these intermediate points created will be above 0dBFS. Even in 2003, the paper listed a number of albums and showed that quite a few have "hot spots" where the "true peak amplitude", after going through an interpolator would be above 0dBFS. (A NOS DAC doesn't do digital intersample interpolation but could still overload with analogue filters [as per Mans' comment].)

MEASUREMENTS: RME ADI-2 Pro FS as DAC (Part I - output levels & digital filter settings)

After having explored a couple weeks back the ADC capabilities of the RME ADI-2 Pro FS, for this installment, let's start with evaluating the DAC output quality of the device and in the process examine the objective fidelity with audio playback.

Remember, with that previous article, I had already discussed my subjective opinions based on listening sessions. My opinion has not changed in the last number of weeks as I'm still very much enjoying the sound I hear hooked up to my main system. Subjectively, the output sounds very clean, has a neutral tonality and low noise level very much like the Oppo UDP-205 and other high quality DACs. As usual, it will be interesting to compare measured results among the different devices I put through the test bench.

But before we do that... Let's start with the basics and some of the "microscopic" measurements I usually begin with - things like output levels, filter settings, etc...

MUSINGS / MEASUREMENTS: About THD(+N) and standardizing testing here... (With a taste of the RME ADI-2 Pro FS as DAC...)

Last week, when I published my look into the RME ADI-2 Pro FS ADC performance, I started using SpectraPLUS for measurements in high resolution for THD and THD+N. I know, it's an old measurement and everyone does it. I realized shortly after publication of the article that while I was using the same technique to measure the RME vs. Focusrite ADCs, I had the ADCs running at 192kHz and so issued an addendum that the results included the rising ultrasonic noise from the ADC and not just a reflection of the DAC. Not unreasonable as a comparison between the two ADCs I think, but this would not be fair to the DAC or other component measurements since much of the noise would be arising from the ADC stretching out to a 96kHz bandwidth. It's worth taking some time to think, going forward, how I could improve the usefulness of this test and in a standardized way here when focusing on whatever device is being tested...

If we look around, we see that the THD+N spec is probably the most used objective "number" for audio equipment as a quick snapshot of fidelity. The THD (page on calculation, how it's done) component tells us whether harmonics are being added to the sine wave at the integer multiples of the fundamental frequency (these are the results of "nonlinearities" in the equipment), and the +N piece adds the noise component found in the signal being tested which of course is also subject to noise limitations of the measurement device and the computational limits of the FFT technique used. In essence, the THD+N ratio is a representation of everything that's being added to a simple single-tone test which of course has its limitations as a test paradigm as well when real music is far from static.

MEASUREMENTS: RME ADI-2 Pro FS ADC performance and as measurement hardware.

I discussed the features and some listening impressions of the RME ADI-2 Pro FS ADC/DAC a couple weeks ago. As I noted at that time, my main aim in owning this device is for the purpose of using it as an ADC for measurements here on the blog going forward.

For the purpose of measurements, we want a tool that can allow us to obtain reproducible results and good accuracy. Over the years, I've achieved reproducible results with consistently minimal inter-test variation by standardizing the way I run most measurements with the digital sources, cables, standard procedures, and types of tests I run. What I want is better accuracy - an ADC that has lower noise floor for improved resolution, doesn't add as much of its own distortions, have higher timing accuracy (eg. for jitter tests), and perhaps more features to expand the measurement quality (eg. higher sample rate to capture impulse responses more accurately, and can handle wider input levels for the range of devices tested).

Given that this is the priority, instead of measurements of DAC performance first, let's get straight to describing the characteristics of and using the ADI-2 Pro as a measurement tool which means we'll need to get a taste of how well the analogue-to-digital capability performs. Let's compare the results I'm getting from the RME to my previous measurement ADC device over the last couple years, the Focusrite Forte for a sense of the changes in resolution I can expect from the new upgrade.

Update: Raspberry Pi 3 B+ "Touch" Streamer, JustBoom Digi HAT, 3.0A power supply... And did they mess up Coltrane's "Both Directions At Once" in hi-res!?

Back in early 2017, I documented on the building of my little Pi "Touch" music streamer that I've been using over the last while for playback through my Logitech Media Server system at home. Over the last year, I've used this quite a bit for music playback and also some of the testing I've done on this blog.

As some of you may know, there has been an update of the Raspberry Pi 3 to the B+ model (~US$40). The upgrade isn't a major change to the existing Pi 3 board. However the new SOC, based on the Broadcom BCM2837B0 quad-core Cortex A53 (ARMv8, 64-bits) is slightly faster at 1.4GHz (1.2GHz previously, about 15-20% speed gain), and another upgrade is better ethernet speed which supports gigabit link but since it's still communicating through the USB2.0 port, will max out at ~300Mbps. In some benchmarks I've seen, though not true gigabit speed, the throughput is about 2x that of the previous Pi 3. For those interested in wireless connectivity, there are upgrades in the WiFi and Bluetooth departments as well.

PREVIEW: RME ADI-2 Pro FS AD/DA Converter

I. Prologue

For those who have followed along on the blog, you may recall that this blog started with some arguments I had with folks on an audiophile forum around the audibility of high bitrate MP3. Back in those days (err... late 2012), there were all kinds of claims made by quite a few hobbyists that they could "easily" differentiate lossless FLAC from 320kbps MP3. I'm sure there are still many in the audiophile forums who hold this view although I think things have softened about the magnitude of differentiability (I think this shift has changed with high-res audio as well).

That disagreement was enough to push me to put out a blind test, to start looking into what I could do to help further my own understanding and awareness around audio hardware. The articles on this blog basically have been the culmination of that pursuit in hopes that the ideas and tests have been useful for others also on this journey looking for some clarity, typically found with more objective analysis.

Objective testing requires disciplined procedures and tools. Methods to reduce variables so that we can have reasonable "apples-to-apples" comparisons and reduce or eliminate psychological biases when we make decisions and search out facts beyond opinions colored by idiosyncratic preferences. Whether it's using an ABX tool, asking a partner/spouse/family/friend/neighbor to change something without our knowledge when listening, or measurement devices - letting the tool demonstrate changes - I believe we can find answers to uncertainties or prove claims. I personally believe objective testing is not only something "nice to have" with reviews, but an essential part of developing insight into the devices being tested and our own perceptual and cognitive limitations.

That's a long intro which brings us to today's preview of a new tool. :-)

When it comes to using an ADC for measurements, over the years, I've gradually upgraded starting with my old Creative E-MU 0404USB from 2012, to the Focusrite Forte in 2016, and now, let's start with a look and listen to the RME ADI-2 Pro FS ADC/DAC. The aim has been that each step brings with it more accuracy for the measurements and this third iteration of the measurement hardware should bring with it opportunities to explore further and continue the process of finding clarity in a hobby that for too long IMO has been filled just with mere opinions - or even worse perpetuation of myths. (Remember, nothing wrong with opinions... But let's make sure it's grounded in objectivity!)

Local Audio Store Visits: Liquid Sound, Vancouver. (And engagement with high-end audio dealerships...)

Well, it is summer and today I thought I'd post something a little "lighter", "softer" and I think more typical of audiophile blogs :-).

I was thinking the other day, I'm fortunate to be living in Vancouver where despite the decrease in brick & mortar hi-fi audio stores over the decades, there are still a number of stores in town that have listening rooms and show off some high quality equipment. In fact, I live less than 10 minutes away from the Headphone Bar (article on Inner Fidelity a few weeks ago). Over the years, I've also talked about local places like Hi-Fi Centre and Commercial Electronics - both about 30 minutes away. If I head in a somewhat different direction from home, further west, we get to Liquid Sound along West 10th Ave.

Obviously, based on my writings, tests and listening, I have a "more objective" take on the audiophile hobby than the "mainstream". I have not seen any large polls but I suspect that the number of audiophiles who appreciate objective analysis might be rather significant.

There is something to be said about knowing about the local dealers and having the opportunity to visit, see, feel, and hear the latest on offer out there. Likewise, I think the local dealers need to check the "pulse" of the audiophile hobby and appreciate the demographic characteristics especially as the typical Baby Boomer audiophiles age. This IMO includes engaging the "more objective" folks who might be more than a little turned off by obvious hype and pseudoscience.

DEMO / MUSINGS: Let's listen to some jitter simulations with sideband distortions...

A couple weeks ago, we started getting into the topic of jitter and the concept of whether jitter is audible and at what level. As I had expressed at that time, my belief based on experience with the equipment I have looked at / listened to is that with almost any reasonable modern day digital audio device, the likelihood that one would hear sampling jitter effects is extremely unlikely. No need for crazy expensive cables that claim jitter improvements. No need for high-priced servers (like this), expensive streamers, or "de-jitter"/"reclock"/"regen" devices. But one of course does want to have a good DAC with excellent jitter rejection, and these days, competent asynchronous USB devices almost universally will achieve excellent results by reducing jitter from the interface (remember, the older S/PDIF digital interfaces typically perform worse than modern USB or ethernet even though newer devices like the Oppo UDP-205 perform excellently with any of the inputs).

The reason I say this comes not just from measurements and my own listening to devices with different severities of sampling jitter, but also experimentation over the years in simulating the distortions introduced by jitter.

As I mentioned last time, with Yamamoto2002-san's WWAudioFilter, we can easily use DSP to introduce fixed amounts of sinusoidal periodic jitter to "bake in" the kinds of sideband anomalies often found with devices that suffer from jitter. For today's post, what I want to do is provide some test files you can use to actually hear what severe jitter distortions with sideband anomalies sound like. Think of this post as similar to one years ago when I demonstrated what poor USB cables sound like.

Furthermore, coming out of this article, I hope the audiophile reader can appreciate the magnitude of jitter that is necessary in order for the effect to become audible. In so doing, I hope it will help us appreciate the results from the J-Test FFT's I publish here and also when you look at measurements elsewhere (like on Stereophile).

"MQA-CD x UHQCD" Listening Test by Agitater.

[Editor's Note: As you may have read in the last few months, there is a new variety of "MQA-CDs" released into the wild. Here in the West, we have seen the new release by Steve Reich Pulse/Quartet contain MQA encoding (playback FFT commented on here). In Japan, a series of MQA-CDs have made their way into public hands from Warner, called "MQA x UHQCD" (UHQCD stands for Ultimate HiQuality CD) which is basically a combination of MQA encoding + "better material" on what is still basically a standard "compatible" CD with 16/44.1 PCM data at premium prices. I guess this kind of thing still interests Japanese audiophiles!?

Techmoan did a review of these which IMO missed the mark as the reviewer clearly does not understand the limitations of MQA itself and believes it really is a "high resolution format" which is IMO false as previously discussed. He also used a glitching portion of Brothers In Arms as a gauge that the MQA-CD sounds "better" through the Pro-Ject Pre Box S2 rather than normal playback (clearly the MQA decoding and filtering changed the output amplitude on the Box - the MQA playback sounded louder).

Techmoan's video did not really compare actual CDs already on sale for years with these new MQA/UHQCDs using higher quality equipment - he just used a computer setup and headphones, obviously having trouble getting things working. To "fix" this situation, here's Agitater and his buddies on Steve Hoffman's Forum! With his permission, I've posted in full his detailed listening sessions conducted with audiophile friends on very high quality systems. Slight editing with headings added for the blog format. A beautiful write-up that just had to be shared and not get lost within a message forum!]

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Asked and answered . . . Here are my music listening group's listening notes and conclusions about the following four UHQ/MQA-CD releases. The albums are, in order below Moanin' by Art Blakey & The Jazz Messengers, Blind Faith the eponymous album by the early supergroup Blind Faith, Getz/Gilberto by the studio trio of Stan Getz, Joao Gilberto and Antonio Carlos Jobim, and Aja by Steely Dan.

Here's the DAC. It's a MyTek Brooklyn DAC+ with fully switchable MQA filter. Note the little, blue MQA indicator light. It was used in all of the listening sessions in a variety of systems, and acquitted itself brilliantly. Note that one of many peeves related to MQA DAC implementations is that the MQA filter can't be turned off and is applied to all streams including non-MQA (standard?) CDs. MyTek made its licensing deal with MQA, obviously, but in the process has retained its own superb filters. That's my Benchmark DAC3 HGC (unused in these listening sessions) below the Brooklyn DAC+.