MUSINGS: Do we "need" those >20kHz ultrasonic frequencies for high-fidelity audio?

Recently I received this excellent question and link about ultrasonic frequencies from the Computer Audiophile site:

Hi, Archimago. Visit your blog frequently and find your posts enlightening and entertaining at times without the usual smoke and mirrors.

What caught my eye in the musings on MQA utilizing the Mytek Brooklyn DAC was the selection of a musical reference which had ultrasonic, specifically musical, content. After reading the paper by James Boyk <https://www.cco.caltech.edu/~boyk/spectra/spectra.htm>, ; I have been interested in the subject of ultrasonics and their (potential) effect on the listening experience fully recognizing that these frequencies are well above the capability of human hearing. Included would be identification of recordings that have musical ultrasonic content.

Given that formats such as PCM (24/96 or higher) and DSD (2x or higher) [Ed: remember that even DSD64 1x can go >20kHz] have the potential to capture musical content above 20kHz, I am intrigued by the possibilities. As with all HiRes formats, I understand that not only all components of the recording chain but also the reproduction chain must have frequency response greater than 20kHz to accomplish this. I do see where speakers are being offered which are spec'd to 40kHz and as high as 100kHz. There are also numerous add-on "supertweeters" being offered which have this capability as well.

IF the topic were of interest to you and worthy of your time and consideration, I for one would be most interested in your musings on the subject.

My apologies for using this Musing as a portal for my inquiry but did not know how else to contact you with the proposal.
FWIW, given the potential of the existing HiRes formats to capture the musical experience if fully realized, I too am less than interested in MQA as the latest flavor-of-the-day.

Frank Zawacki
Connecticut Audio Society

Thank you Frank for the link, interesting discussion and question. I try to do what I can to collect information and synthesize posts to provide hopefully reasonable thoughts on these matters; mixed with some measurements and personal subjective impressions as appropriate.

HOWTO: Building and Installing the Raspberry Pi 3 "Touch" Audio Streamer.

Raspberry Pi 3 + 7" Touchscreen (left) and Squeezebox Touch (right): for the Pi device, I still had the plastic screen protector on in the picture, hence the bottom left tab...

I showed you guys this picture last time of the Raspberry Pi 3-based Streamer device with official 7" touchscreen and HiFiBerry DAC+ Pro. As you can see from the image, it's very much capable of being a "clone" of the Squeezebox Touch. Furthermore, it's highly affordable with even more hi-res audio potential such as the capability to stream bitrates beyond 96kHz (remember, the stock Touch goes up to 96kHz, enhanced to 192kHz with Triode's EDO plugin).

In this post, let's have a closer look at the device and some instructions / suggestions to build one.

MUSINGS: Computer Audio Part II: The Basics & Suggestions

For many readers, I'm sure what I'm about to write here is relatively "old hat" by now... However, in the spirit of "Computer Audio Demystified" last week, let's talk about this powerful way of storing, categorizing, and playing our music by exploring some aspects of the foundation of computer audio in a way I hope newcomers will find reasonably accessible. I do make some assumptions in the writing that the reader has some basic knowledge of computer usage and networking. Let's consider the "architecture" of what someone might want to build, and a few reasonable options if we were to start from scratch with full disclosure of the price to build such systems.

I can imagine that some folks might need to overcome their phobia around computers. If you're motivated, just put in some time, a little patience and don't be afraid to "play" with it. More likely than not, once one has tasted the convenience and have found one's "groove", going back to only spinning physical media will likely feel archaic after a short while :-).

First, permit me to remind everyone about the two most important determinants of sound quality in a high fidelity audio system:

1. Put thought and money into good speakers, good pre-amp/amp(s), good DAC and a good sounding room.

2. Make sure the system is acoustically quiet; ideally silent.

Point 1 is obvious. The primary factors in sound quality (ie. "fidelity" achievable) are the room, speakers, and amps in that order - these are the prime candidates for sound distortion, not your computer or DAC (and certainly not stuff like cables). And Point 2 is an obvious corollary for any equipment we put in the room since we don't want the system itself to act detrimentally - this includes noisy computers, buzzy amp transformers, ground loops through the pre-amp, etc. Remember that the purpose of computer audio is simply about storing the audio library data reliably, making available a conveniently handy user interface, and the bits are being delivered in an accurate fashion to the DAC; whether internal to the computer audio device or say an external USB DAC. There is no mystery in how to come up with a solution to achieve these goals.

MUSINGS: Computer Audio Part I: Demystifying "Computer Audio Demystified"

It's nice to see that some of the seminars at the Rocky Mountain Audio Fest (RMAF) 2016 have been posted on YouTube. It gives all of us who may have wanted to visit a chance to review the "latest and greatest" tips and updates...

Although the RMAF is hosted by the Colorado Audio Society, remember that much of the material comes from Industry; with of course the potential for vested interests influencing the content. I think many visitors to this blog would be interested in computer audio, so let's spend some time looking at the information disseminated... For your consideration, let us explore the one presented by Steve Silberman of AudioQuest - "Computer Audio Demystified" (RMAF 2016):



Feel free to watch the full 1.5 hours. For today's segment, we'll look at a bit of reality testing vs. myth vs. mysticism. You'll notice that the comments section for this video on YouTube has been turned off. Interesting. How else to discuss the contents then than in a blog post like this, right? :-)

MEASUREMENTS: A look & listen to Roon Bridge - Raspberry Pi 3 Streaming (HiFiBerry DAC+ Pro & USB DAC)

Last time, I talked about Roon and discussed my experience with it using the NUC as the primary installation and playback. No doubt, you are aware that many people will use inexpensive devices like the Raspberry Pi 3 to handle playback distributed around one's home... And no doubt you've also come across much hyping about more expensive, low power devices when for around $100 and a little know-how, you can get it done quickly, easily and sounding great.

First, I just wanted to practically lay out a simple way to install Roon Bridge on the Pi 3 that worked for me and using which I will run a few tests to demonstrate the sonic output. Remember that the network protocol from the Roon "Core" (my Windows computer) to the Roon "Bridge" (Pi 3) is what's called RAAT (Roon Advanced Audio Transport). It's a protocol with a number of benefits as highlighted in the link.

MEASUREMENTS: Roon 1.2 (with Intel NUC 6i5SYH)

NOTE: I know that just a couple weeks ago, version 1.3 of Roon has been released and I'll perhaps look into that a bit later once some of the initial bugs are stamped out and the system matures a little. Clearly 1.3 has a few new interesting features but the basic bit-perfect playback function I trust would be the same which is what I'm aiming at exploring in this article.

Over the last few years, I have already gradually made my way across the different audio ecosystems that most audiophiles find themselves interested in. Starting with the venerable Squeezebox / Logitech Music Server system (eg. Touch, Transporter), to standard Windows PC and Mac OS X playback, to questionable software (like JPLAY and the JPLAY update), to even just as questionable OS tweaks (eg. Fidelizer), to more recently looking at DLNA streaming using low power devices like the Raspberry Pi 3 and ODROID-C2.

For today and the next few weeks (let's see how this goes), let's spend some time on Roon, another computer audio system much lauded in the audiophile press and see if we can make a few measurements and comment on some observations and thoughts...

MUSINGS: Discussion on the MQA filter (and filters in general)... [Update: Including a look at the classic "Apodizing" filter.]

Here's an interesting comment from the post last week...

CBee 7 February 2017 at 04:47

Excellent article but I have one query. On Sound on Sound they say "MQA claim that the total impulse-response duration is reduced to about 50µs (from around 500µs for a standard 24/192 system), and that the leading-edge uncertainty of transients comes down to just 4µs (from roughly 250µs in a 24/192 system)." In that case wouldn't you need an ADC with higher resolution than the RME Fireface 802 in order to see any real differences between the Reference and Hardware MQA decode?

As I said... Dammit CBee! Now you've made me post another blog entry on MQA :-).

COMPARISON: Hardware-Decoded MQA (using Mytek Brooklyn DAC)

As promised in my last blog post about software MQA decoding, I have been wanting to have a peek and listen to hardware decoding. Due to the proprietary nature of the MQA firmware as well as the fact that we don't have access to MQA encoder software, there is only so much we can do to explore the effect on an audio signal. Ideally, encoding a test signal and then decoding would be the best way to explore the effects and limits of how this all works...

I don't have an MQA-capable DAC myself (and honestly owning one is not high on my list of priorities), but a friend does happen to have the Mytek Brooklyn which is fully MQA-native and has the ability to decode all the way to 24/384. Furthermore, he has the use of a professional ADC of fantastic quality - the RME Fireface to make some recordings of the output from the DAC.

Image from Mytek. Obviously very capable DAC!

With the combination of the excellent DAC and ADC, we should be able to examine the output and make some comparisons. The main questions being:

1. Can we show that hardware-decoded MQA is closer to an original signal beyond the 88/96kHz decoding already done in software?

2. Can we compare the hardware decoder with the output from the software decoder? How much difference is there between the two?

QUICKIE POST: Yes, cables matter... (for HDMI 2.0/4K/60fps/HDR...)

Well, of course cables matter! Without them there would be no sound or image! The key of course is to be wise enough to have a concept of what is needed, and how much difference the cables/wires can make.

Just a reminder, if you have not seen it yet, here is my summary of tests and thoughts on audio cables over the years if you're wondering about that.

As for today, given that time is limited this week, I just wanted to put up a "quickie" post mainly about some 4K HDMI cables I tried over the last couple months in setting up my 4K TV (a Vizio P75-C1).

MUSINGS: On the ongoing push for high resolution audio... and the virtualization of media.

Thanks Sony for this BS diagram... Except for the most primitive non-oversampling (NOS) DAC's out there, more likely than not, DACs these days utilizing antialiasing filters of course do not output their analogue like these stair-stepped waves. Sadly, these kinds of diagrams often become the marketing material used to push hi-res! Can good outcomes result from marketing with dubious claims? (Didn't seem to help Pono, did it?)

I didn't have much time this week for any experiments/measurements. Alas, will be busy for a little while still. Which means it's a good time to put up a "MUSINGS" post based on comments and questions. Always fun to take some time to think and hopefully flesh out ideas a little more. In the post last week, I found these interesting comments worth spending some time on:

COMPARISON: TIDAL / MQA stream & high-resolution downloads; impressions & thoughts...

As I mentioned last week, and I'm sure you've seen all over the audiophile news, TIDAL has started streaming MQA audio and has embedded a software decoder into the Windows/Mac desktop player. It will basically take a 24-bit 44kHz or 48kHz stream that's encoded by MQA and spit out an 88kHz or 96kHz data stream to send out to your DAC; whether the internal one in your laptop, or a fancy external DAC with options for "Exclusive" mode which allows changes to the appropriate samplerate (I know this works well on the PC, have not tried the Mac).

If you're not using "Exclusive" mode, you can tick "Force volume" to set it to 100% volume so the internal mixer/dither routine hopefully doesn't mess with it. "Passthrough MQA" should be ticked only if you have an MQA enabled DAC or want to purposely hear MQA undecoded (I'll say it now that this is not recommended). My assumption is that if you do have one of these MQA DACs and passthrough is on, you should either make sure "Exclusive" mode is ticked or if not, manually make sure the OS samplerate is correct (ie. 44kHz or 48kHz at 24-bit depth) and that the volume is 100% (either with "Force volume" or making sure the computer volume slider is 100%). Otherwise, it will not be "bit-perfect" and the DAC will not recognize the MQA encoding. I suspect this could be confusing for some.

MEASUREMENTS: Raspberry Pi 3 as USB Audio Streamer (with recommended CRAAP config & TIDAL/MQA arrives)

A few weeks ago, I got this question from Josh Xaborus in my previous post on the Raspberry Pi 3 + HiFiBerry DAC+ Pro measurements:

Have you measured the USB output from the RPI3 to a USB DAC to see if it's "clean" like the ODROID?

Good question Josh, and perceptive as well. I had not posted anything on the Raspberry Pi 3 specifically, whether there was any difference to be found streaming to the same USB DAC as compared to say the ODROID-C2. Let's have a good look at this and see if we can arrive at some facts and come to some conclusions...