Sunday, 2 October 2016

MEASUREMENTS: Raspberry Pi 3 & HiFiBerry DAC+ Pro (Audio Streaming)


Last week in the preview, I introduced you to the Raspberry Pi 3 Model B with the HiFiBerry DAC+ Pro HAT board. You see above a picture of the boards assembled but in the "naked" state before installation in the case. As I mentioned it doesn't take much time to put this all together on the hardware side, and just a bit of tinkering with Volumio 2 was all that was needed afterwards to get the DLNA/UPnP streaming working over the wired ethernet (a little fiddling with the Volumio hotspot if you want to use WiFi - not recommended for hi-res audio). Since the software is still in development, I noticed that messing with network settings could lead to connection issues. But once it works, it has been stable.

As promised then, let us now put this device to the test and see how it performs objectively. What level of "high fidelity" does this streamer/DAC combination perform at?

Before getting to the results, let's start with identifying the test set-up. It's really quite simple, the Pi 3/DAC+ Pro combination is running off the latest Volumio 2 version for Raspberry Pi - 0.979 release date 20-08-2016, essentially running off default settings. I'll be streaming off the wired ethernet, generic Cat-5e cabling used to connect to an inexpensive D-Link DGS-1008G gigabit switch (remember the Pi 3 is 100Mbps only) which is then connected by Cat-6 to my main router in the basement, a NETGEAR Nighthawk AC1900 R7000.

On the server side, I have my usual Windows 2012 R2 server running JRiver 22 on my "old faithful" AMD A10-5800K-based computer, 16GB DDR3 RAM, put together back in 2012 when that CPU first came out.

Literally what I'm measuring! Pi 3/DAC+ Pro, generic Fujifilm-branded switching power supply (5V, 1A) from an old camera charger, generic USB-A to micro-USB cable. Regular (Nexxtech "Radio Shack" to be exact) 3' RCA cable.
Measurement chain:
Pi 3/DAC+ Pro --> 3' RCA cable --> RCA-to-TRS adaptor --> Focusrite Forte ADC line level in --> shielded 6' USB cable --> Win10 laptop
Remember, this is being measured with my new Focusrite Forte device so don't compare these results directly with the old Creative E-MU 0404 measurements over the years - results will be close but not exactly an "apples to apples" comparison. All comparisons I make on this page will of course be consistent in terms of measurement technique.

JRiver 22 streaming to Pi 3/HiFiBerry DAC+ Pro/Volumio.

Part I: Digital Oscilloscope, Digital Filter, Impulse Response

With the output volume set at 100%, we start with a look at the 1kHz 0dBFS square wave on the oscilloscope:

As you can see, the peak voltage is around 2.95V or ~2.1Vrms. Left and right channels directly overlay on each other, demonstrating precise channel balance. Given the symmetrical shape of the square wave transition, we're likely looking at a standard linear phase digital filter.

Here's the impulse response:

Indeed. Linear phase impulse response with symmetrical pre- and post-ringing. Given the amount of ringing, we can expect this to be a reasonably sharp filter. Notice that polarity is maintained (input signal was a positive impulse).

A look at the "digital filter composite" then:

Yes, we are in fact looking at a "sharp" anti-aliasing digital filter. It's not the cleanest FFT I've seen but I'm not one to claim too much about the audibility of digital filters based on what I have heard and measured. Note that there is evidence of intersample overload with the high amplitude white noise signal using the HiFiBerry. Though not ideal performance, remember that I am using white noise with peaks up to 0dBFS which is more demanding than the -4dBFS noise signal used in the Stereophile article where Juergen Reis introduced this form of testing. Realize that this is not necessarily a problem with good mastering allowing overhead for full dynamic range, but I suppose for poorly mastered audio with amplitudes near clipping for large portions of the music, this digital filter could exacerbate distortion.


Part II: RightMark Tests

Okay, let's have a look now at the noise/dynamic range and distortion levels at various samplerates and bit-depths.

16/44.1:
Good old CD resolution. Any decent DAC must be able to do this well!

As you can see, I'm comparing the HiFiBerry with a number of other devices like the TEAC UD-501 desktop DAC, the Light Harmonic Geek Out V2 USB DAC, the PonoPlayer mobile device, and the Focusrite Forte's DAC itself as an example of "pro" gear.

What can I say? They're all performing very well numerically. Essentially ideal low noise level and excellent dynamic range across the board. This is to be expected as they're all capable of hi-res performance. This is of course not to say they all sound the same :-):


As you can see there are some idiosyncrasies among the devices. The PonoPlayer has high frequency roll-off. The Focusrite Forte's stereo crosstalk isn't as nice as the others, and the IMD+N distortion is higher for the HiFiBerry DAC+ Pro. In regards to that, realize that the IMD+N distortion is still measured as averaging just 0.032% so this is more interesting from an academic perspective rather than a worrisome finding in actual listening.

24/96:
Time for high-resolution. Here's the summary:

As above, here are some graphs taken from the data:

Interesting. In terms of noise characteristics and dynamic range, the HiFiBerry DAC+ Pro is really quite excellent. It's actually similar to the more expensive TEAC UD-501 and Focusrite Forte than the PonoPlayer and Geek Out V2. Certainly very close to the noise floor limit of the Focusrite Forte around -110dB averaged across the audio band. What is also interesting again are the higher distortion results for the HiFiBerry and most evident in that IMD+N sweep graph (you see this in the THD distortion number also). Again, we're not talking about a massive load of distortion by any means, but it is significantly higher than I've seen with most DACs these days.

24/192:
This is the highest resolution setting for the HiFiBerry DAC+ Pro.

Just a couple of the graphs (RightMark doesn't handle the 192kHz graphs well):

Again, there's a bit more measurable distortion - in both THD and IMD in the HiFiBerry DAC+ Pro than compared to the likes of the TEAC UD-501 or the Geek Out V2. Otherwise we're still looking at a device with excellent dynamic range with concomitantly low noise level.

Part III: Jitter

As I mentioned last week, the I2S interface is still vulnerable to jitter depending on the quality of the master clock being supplied to the DAC. The HiFiBerry DAC+ Pro incorporates its own high quality oscillators for the 44.1kHz and 48kHz families of samplerates. In principle, this should give good results on tests of jitter...


That looks excellent. The 16-bit test shows the expected jitter-modulation tone in the LSB. The 24-bit J-Test (24/48 signal) looks good, completely free from spurious tones from 5-18kHz with the primary signal at 12kHz. Okay, how about we add further "stress" to the system by accelerating the jitter test tone to 24/96 - I started looking at this with the Google Chromecast Audio a number of months back.


This looks excellent. There's a noise peak down below 14kHz. The fact that the primary signal at 24kHz is arising without much "tenting" and the lack of symmetrical sidebands is testament to the excellent timing precision. (Just look at the Chromecast Audio using TosLink output to see what jitter will look like with this rather extreme version of the J-Test.)

Part IV: Battery Power!


Well, 5V lithium ion batteries are easily accessible these days to charge USB devices. As I showed a few months back with the ODROID-C2, a little battery like the Duracell above has enough juice to power a computer like the Pi 3 for probably a couple of hours (depending on how much processing being done of course). And since these days my Focusrite Forte can be run directly off the computer's USB port, the measurements can be done completely without plugging into a wall socket.

So, does running off battery power result in any improvement to the analogue output?

Let's look at the 24/96 and 24/192 results for hints:

As you can see, the "Batt" tests are with battery power versus a 5V switching power supply. Results are almost exactly a match... You can maybe make a case for insignificant reduction in the distortion results when run off the battery. People talk about switching power supplies causing noise, so let's scour the 24/192 noise floor:
Note: That noise at 37kHz originates from the ADC as previously documented and is not an issue with the Pi/DAC+ Pro.
Nope. Nothing to see... Notice the 60Hz hum (peaking way down at -130dB) is exactly the same whether using the switching power supply or lithium ion battery! [Remember this... I know where this comes from and you'll see this discussed in another blog post later :-)]. Plus there's no evidence of extra noise in either case all the way to at least 50kHz before we see the ADC noise floor rise!

And as for the distortion graph (the IMD+N Sweep):

No significant difference between battery or switching power supply either...

Is this surprising? I don't think it should be. This is the same result I got with the ODROID-C2 previously but given that the ODROID was just streaming to an outboard powered DAC (the TEAC UD-501), perhaps that wasn't unexpected. This time, we see no difference even with an internal DAC running off the same switching power supply.


Part V: Conclusions

As I noted in the preview last time, the combination of a Raspberry Pi 3 with the HiFiBerry DAC+ Pro is an easy-to-assemble box which as I have configured with Volumio acts as a low-power and reliable DLNA/UPnP audio streamer capable of 24/192 output to one's hi-fi system. Of course, one could use it like the ODROID-C2 and send the audio out using the USB interface instead without purchasing the DAC daughterboard.

I've had this unit running for about 3 weeks now and it does sound great as I noted last week. It has been reliable running 24/7 in the soundroom and is reported by my Kill-A-Watt P3 meter as sipping at most 4W when booting up, and typically uses only ~50mA.

Let's then run through a list of some "take home" points from this series of measurement results:

1. The HiFiBerry DAC+ Pro, despite being a daughterboard connected over a Raspberry Pi 3 computer puts out very low noise, high dynamic range analogue unbalanced RCA output. It's not the absolute best I have measured but certainly very close to much more expensive DACs. Clearly, the DAC+ Pro is capable of benefiting from true, high quality, high-resolution 24-bit audio files.

2. Excellent channel balance noted on the oscilloscope reading. Though not shown, this precise L-R amplitude balance was maintained throughout the volume range. Maintaining channel balance is of course very important for soundstage "image" stability.

3. This DAC's digital filter does things "by the book" with a "ruler flat" audible frequency response. The antialiasing filter is an "orthodox" linear phase steep filter, likely one of the presets in the TI/BB PCM5122 chip and I suspect the "digital filter composite" graph is a reflection of the Burr-Brown design. As I mentioned above, it's not the nicest measuring digital filter with evidence of intersample clipping in the oversampling process; a technical finding which doesn't necessarily correlate with audibility. (For an example of what an essentially picture perfect "digital filter composite" graph looks like, check out the Light Harmonic Geek Out V2 based on the recent 2015-released ESS SABRE9018AQ2M DAC chip.)

4. When making comparisons, it is interesting that the HiFiBerry DAC+ Pro's harmonic and intermodulation distortion results are higher than others I've measured over the years. Realize of course that the magnitude is still very small compared to the amount introduced by one's speakers or room acoustics (is anyone going to hear 0.03% THD+N distortion?) - but worth noting as a fidelity "perfectionist". I wonder if this is a limitation of the PCM5122 chip itself. On the other hand, I am impressed by the very low stereo crosstalk with this DAC; one of the best I've seen. Not that this is audible of course, rather it speaks to the quality of the device and the well controlled noise levels.

5. Jitter is not a problem. Higher jitter can be found on S/PDIF interfaces and old synchronous USB devices. These days with typically asynchronous USB, ethernet, and this I2S board with its own oscillators, there's generally nothing to worry about.

6. Raspberry Pi 2 vs. Pi 3 for audio - distortion from wireless transmitter? Some have said that the inclusion of WiFi and Bluetooth in the Pi 3 makes it less suitable for audio applications due to distortion... Realize that I have made all of the above measurements with the WiFi module "on"! Yes, I have measured the noise floor with WiFi off also:
Raspberry Pi 3 & HiFiBerry DAC+ Pro: WiFi ON vs. OFF... Perhaps I'm mistaken, but I don't hear a difference in the noise floor :-).
As you can see, it makes no difference to the DAC+ Pro's analogue output (nor a difference to distortion results). IMO, this is another one of those "possible" issues raised by anxious audiophiles that really has no basis in reality... If it did, I think it would be nice for someone to document this so we can all avoid such gear.

In my opinion, the benefits of the faster Pi 3 (~50-60% increase on a processor intensive benchmark like Whetstone), inclusion of the 64-bit instruction set, with built-in wireless ability I think are worthwhile upgrades over the Pi 2. By now, it's also even cheaper than the Pi 2.

7. Value. Remember what we're talking about here. A self contained streaming device that can operate in WiFi or through wired ethernet, demonstrably capable of high-resolution playback up to 24/192, uses minimal electrical power, known to be reliable, easily purchased through on-line storefronts, and is priced currently just over US$100! Realize that I'm putting this little computer & DAC board up against devices costing much more... Even the Light Harmonic Geek Out V2 DAC costs ~$300 and you'll still need to have a computer to go along with it. A self-contained PonoPlayer would cost ~$350 but it's for a totally different purpose. I think it's also worthwhile remembering that there's an opportunity to repurpose the Pi 3 in the future should you want to try making it into a video streamer for example (like with Kodi). Furthermore, with the power of open-source development, you could convert this to be a Squeezebox-like streamer or Roon endpoint.

Looking around the internet, I see this video review from Hans Beekhuyzen for the DAC+ Pro. He claims the sound was poor without the use of a linear power supply (starting at 2:50 - "Not the sound I expected... Not by a long shot... I don't want to review stuff at this low a level...")!? Hmmm... Unless there has been a change in the board revision (mine says "HW 2.2" on the board), or he used some remarkably poor switching power supply, I see no evidence of a problem personally. Maybe he should take a moment and use the testing equipment in the background of the video and see what he finds... IMO, there's no reason to bring up questionable pet theories like the "water organ" analogy and claims of "voltage of the power supply not constant" as the rationale for vague subjective impressions. What evidence is there to support the claim of "stunning" improvement such that he's suddenly "enthusiastic" to compose a review!?

Linear power supplies are expensive, they're also much less efficient and larger - all characteristics very much antithetical to the benefits of the small, efficient, and inexpensive Pi/HiFiBerry that can be left on 24/7! Myths are plentiful in this world and I see no need to create or perpetuate ones around engineered products without actual evidence. I do recommend reading Benchmark's post on the "Switching Power Supplies are Noisy" myth for a rational second opinion on this. Make sure to watch the video also.

Based on these results and my subjective impressions discussed last week in the preview, I think it goes without saying that I'm impressed at the sound quality at the affordable price point. Sure, one could spend more for better measuring gear as per the comparison charts above but if we're just talking about sonic fidelity, I think we could put the Pi3/DAC+ Pro in a blinded, volume controlled session against other much more expensive streaming devices and DACs and not feel embarrassed in the least!

Of course, as discussed in the past, people will spend money for non-utilitarian reasons beyond fidelity and that's fine too...

-----------------

In the last few days before publishing this, I've been running piCorePlayer (latest 3.02 version, September 2016) and using the Pi3/DAC+ Pro combo as a "Squeezebox replacement" in a system upstairs. Kudos to the team that brought this together! Very stable so far and excellent web-based set-up. Great stuff. (And yes, I ran a quick measurement demonstrating identical results at 24/96 and 24/192 as with Volumio.)

As much as I enjoy the power and DSP abilities of JRiver, good old Squeezebox/Logitech Media Server remains rock solid, running strong and stable for years now. Even better since I got digital room correction running earlier this year with BrutefirDRC.

Over the last couple nights, I have been listening to Macy Gray's recent Stripped (2016) album, which includes jazzy covers including her own song "I Try". No doubt the recording quality is excellent from the Chesky label. However, the "binaural+" dummy head recording is clearly meant for headphone listening. It really sounds strange through a speaker system with instruments appearing well placed but the vocals diffused without a sense of being able to imagine the person singing in the front soundstage! I guess Chesky must be targeting the headphone audience with these recordings as a reflection of the rise of mobile music consumption. Anyone know if there is a non-binaural mix out there? It would be a shame if there wasn't a concomitant live recording of the performance meant for standard stereo speaker playback (a multichannel version would also be very interesting I think!).

Happy October everyone! Here's wishing you many joyful listening sessions through the autumn/spring...

44 comments:

  1. Hi Archimago, I have an IQAudio DAC that uses the same TI PCM5122 DAC chip. If you run the alsamixer app in a terminal window on your RPi you can choose your DAC device and cycle through 5 different digital filters the chip supports:


    - FIR interpolation with de-emphasis
    - Low latency IIR with de-emphasis
    - Fixed process flow
    - High attenuation with de-emphasis
    - Ringing-less low latency FIR

    I haven't done a proper blind test, but the Ringing-less low latency FIR filter seems to sound best on my system.

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    1. Cool Jim! Sounds interesting :-).

      Do you or anyone know if the digital filters can be switched easily if I'm just running a headless Volumio / piCorePlayer? Could be interesting running measurements between them...

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    2. Moode has a GUI that supports the switching of filters, and we hope to add that to Volumio soon.

      But for now, just ssh into your RPi, fire up Alsamixer and you can switch between the various digital filters in real-time. The few people who have played around this seem to prefer the Ringing-less low latency FIR as do I.

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    3. Nice Jim! I see it... Will certainly spend some time "looking" into this :-)

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    4. Jim: Any idea what the "Fixed process flow" setting is?

      I don't have any audio output from that setting.

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    5. No idea Archimago. I've found very little documentation on these filters. It's possible there is some explanation in the technical data sheet from TI on the DAC chip, but that stuff is way over my head!

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    6. Hello Archimago,
      many thanx for that article above! Really impressive about the HB DAC+ pro!
      I know, this thread is quite old, but would like to add some note/question.
      When I switch the digital filter of my HB DAC+ pro, using alsamixer (running on RuneAudio_rpi2_rp3_0.4-beta_20170229_2GB.img.gz) I have to reboot the RPI, before the change takes place (measured with M-AUDIO192 soundcard). I am not sure, if the people, who say "Ringing-less low latency FIR , sounds best", do know that?

      Question: Does anyone know a "trick", to switch the digital filter of the HB without reboot? (Please contact me at udamm magicsign gmx.de
      thank you really much!
      Uwe

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  2. Fun! — I love how you take stuff that audiophiles and skeptics usually bicker and beef about, and instead just dive in and creatively explore and measure with an open mind. As with this ridiculously cute and absurdly cheap/tiny rig on the outer limits of miniaturized performance. You just need some fat python-thick high-end interconnects and you've good to go.

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    1. Thanks Hal. Yes, I can just imagine someone putting those "python thick", stiff and heavy cables on this unit and making it absurdly unstable :-).

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  3. Hi Archimago, thanks for this report. I've been using an older RPi/HiFiBerry Digi+/PiCorePlayer for quite some time and have been very happy with it. Sounds the same as any of my other Squeezebox hardware. No problem sending 24/96 via wifi in my system. Nice to see the shout out to LMS; still going strong for me after ten years!

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    1. Good stuff... I assume you must have a good WiFi transmitter on the Pi. The one built into the Pi 3 is convenient but doesn't seem very strong for further distances. I can stream 24/96 in an adjacent room to my router but if I'm upstairs, the connection strength would be too poor for lossless 24/96 FLAC unfortunately.

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  4. I'm running a Pi3 with the IQaudio PiDacZero board and the official 7" screen (with piCorePlayer 3.2). This combination results in a great all-in-one solution (LMS server, touchscreen interface emulating a Squeezebox Touch but with a much better on-board file server and files on a 128GB USB stick) which is superb value for the money! One can also run a USB dac from it, but this adds to the cost ;-)

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    1. Looks like same PCM5122 DAC on the PiDacZero. I wonder what the jitter measurement would look like on this unit without the additional oscillators?

      Anyone know for the HiFiBerry DAC+ Pro if there's a way to turn off the "Pro" feature and see what timing/jitter might look like without those dual crystals?

      Would be an interesting and educational J-Test comparison!

      Delete
  5. I too have been rocking a RPi and HiHi Berry Digi+ (with SDPIF outputs to and old receiver) and have really been digging the sound - ie, it sounds the same as any other digital decent source.

    Its truly a golden age for high fidelity sound - it can be had sooo sooo cheap!

    And don't the audiophiles HATE it! :-)

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    1. Interesting point Qmax!

      I actually would hope that the "true" audiophiles would rejoice that good sound can be available to essentially everyone without the hurdle of price getting in the way. I assume the only folks who might be unhappy with the "golden age" of easily accessible high fidelity would be on the business side who depended on an aura of luxury and desires to maintain a correlation between price and supposed sound quality however that might be defined.

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  6. Those Lithium Ion battery USB power banks have boost converters (Ie SMPS) to boost the ~3.7 of the lithium ion cell to the 5v USB-level output.

    Of course, I think the fact that the results of a cheapo USB powerbank vs a wall-wart, which probably have rather different noise/ripple spectra, are pretty much identical shows that the power-supply noise rejection of the board is quite good.

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    1. Sure... You could be right. I'd certainly love to see measurements from those selling or using expensive linear power supplies though!

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  7. Hi Archimago,

    First let me start off by saying that, unlike some of the other people on this blog, I only discovered this site very recently. But I should say that in that very short time, I managed to find a lot of relavant, objective and ,more importantly, factual information about high end audio. Like many others , I got sucked into the black hole of expensive, and all-too-soon-obsolete hi-fi purchases and upgrades. Your blog has helped me refocus on what turned me into an audiophile in the first place: music, and not the gear itself. So thanks a ton for that.

    after reading through the articles, i was going to get myself an odroid-c2 to serve as a network audio player that would, for the moment, stream directly from JRiver on my Macbook Pro. However, since I do not own any Windows PC or laptops, but often find the need to use/have one (as in the case of EAC which I dearly love but can't use) I was trying to find a mini PC or stick PC that would serve as both a network audio player and a windows PC for those occasional needs. That's when I came across the $99 Kangaroo Mobile Desktop that comes preloaded with Windows 10. Since an odroid-c2 with an SD card/eMMC module, case and power adapter would cost about nearly the same anyways, I was wondering if the kangaroo would be a good alternative to the odroid setup. I already possess the NAD D 7050 to which I can connect either device as an async USB out. Apart from the lack of ethernet port on the kangaroo, do you see any major differences that would affect the audio quality out of the kangaroo? Thanks in advance.

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    1. Hi Deepak,
      A pleasure putting the information out there! I must say that doing this for myself has cured my own "audiophile neurosis" about expensive tweaks and I am glad that it can help others as well :-).

      Now not having a Kangaroo, I of course cannot be sure... However, it does look like a nice machine. The Mobile Desktop with Atom X5-Z8500 processor, 2GB RAM should be much faster than the ODROID-C2 in general processing. The main benefit I see to the C2 would be the 4K/60Hz HDMI2.0 potential for streaming with hardware HEVC decoding. Also, the C2 does have a gigabit ethernet port. Make sure the wireless is strong if you want to stream hi-res 24/96 unless you buy the Kangaroo Pro with ethernet feature.

      Now as for sound, I don't see any reason why there should be any difference connected via USB to the NAD 7050 which based on the manual does have an asynchronous USB interface for up to 24/96.

      Enjoy!

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  8. Thank you for putting together this test, Archimago. Looks better than I expected. RPi + HifiBerry, value for money.

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  9. Hi Archimago, thanks for this excellent review and test.
    I use this combo rpi and hifiberry dac pro whith the distribution max2play.
    Whith the squeeze box server , i listen all my music from anusb HD . The sound is outstanding from this cheap device.

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  10. Very desired test sound equipment.
    If you will be interested to note the new card for audio output from the RPi - "Allo Kali I2S Reclocker". First reviews are very encouraging - https://volumio.org/allo-kali-i2s-reclocker-a-true-gamechanger/

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    1. Interesting. And I suppose this could help clean up I2S jitter from the Pi to a DAC like the HiFiBerry DAC+ (non-Pro, if they fix the supposed driver incompatability). It would be interesting to see the Dunn J-Test results for a DAC+ with and without this device.

      Not sure if it make sense to use this with something like the DAC+ Pro though; especially since jitter based on what I see is not a concern. Ultimately we need to see some measurements :-).

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    2. Of course! It would be very interesting to see the Dunn J-Test results for a DAC+ with and without this device.
      I2S bus from Pi-circuit board has a lot of jitter, here measuring "Comparing the I2S Capabilities of the RPi and Odroid C1+" (http://helios.himmelbauer-it.at/blogs/general/comparing-the-i2s-capabilities-of-the-rpi-and-odroid-c1/), in ODROID slightly better than of Pi, but all the same level > 1ns (1000ps), "Crazy Audio" (http://www.crazy-audio.com/2013/09/raspberry-pi-i2s-output-working/) approximately 800ps showed Raspberry Pi I2S output working, сompare Amanero USB board has 2 ps.
      But developers Kali I2S Reclocker declare < 3 ps output jitter, "New FIFO buffer for RPI/SBCs" (http://www.diyaudio.com/forums/digital-line-level/294940-new-fifo-buffer-rpi-sbcs.html).

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    3. Broadband Time Jitter on I2S or BiPhase Signals
      Thank you for the links, showing some Jitter with High Bandwidth Scopes. Sure, it would be nice to have also low jitter values in those measurements, but this measurements doesn't show you, what frequency content creates those jitter. To judge those measurement, you have to FM and AM demodulate these carrier and make a FFT analysis of the demodulated signal within the audio frequency range. This basic idea is also explained by the late Julian Dunn and is included in the newer Audio Precision devices, where you can see the FFT of the demodulated carrier with frequency on one axis and modulation span at those frequency in the other axis. So you can see what frequency in the audio band does have what jitter. This graph does also take into account, that we do have different sensitivity for jitter for different frequencies.
      Juergen

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    4. To show you one example of what I mean. Here is a measurement of a BiPhase Jitter (measured in the time domain, and not at the analog out of an attached DA converter).

      This signal does have a Time Jitter of 1.246 nS (peak-peak). But what does this mean? Without the above mentioned analysis, not really any real facts.

      And so here is the analysis of the demodulated carrier.

      www.juergenreis.de/FFT-Demodulated-Jitter.jpg

      And here you can see, that in the bass section the jitter is around 100 ps and in the sensitive area of the ear, the jitter is around 3 ps.

      Juergen

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    5. PS: And just a last addition to that. The very first measurements about the jitter "content" (and not only the peak-peak time variation) that I have seen was with the Meitner LIM demodulator. Where you connect the probe to the master clock (of the I2S bus) and set to the right Master Clock to Word Clock Ratio and make an FFT (with the very first Audio Precisions) of the demodulated NF audio signal of the "HF" Master Clock signal. This first method has worked on the I2S bus, where the Audio Precision test does work on the Bi-Phase signal.

      Juergen

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  11. Because of the blog I bought the same case and HiFiBerry DAC+ Pro. I was using a Audioquest Dragonfly Black USB DAC with my RPi3 and Moode. I think the Dragonfly is a little better sounding DAC, but am still undecided. Overall I am very happy with this setup.

    BTW, the system I am using is: The above into a PS Audio Sprout to Paradigm V.5 speakers. I pull files off a NAS. Also run a Rega RP3 TT and Sonos Connect.

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  13. Hi Archimago, thanks for the great info.

    Would it make a difference if you connected a linear PSU directly to the DAC+ Pro as recommended by Hans Beekhuyzen and Scott Kramer, instead of connecting it to the RPI?

    Please see 7:07 on this Youtube video...
    https://www.youtube.com/watch?v=ps-X4ipA_fY

    Thanks.

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  14. There is a problem with 24/96 and 24/192 measurements of GO V2 - they are way different from the ones in http://archimago.blogspot.co.il/2016/07/measurements-focusrite-forte-usb-audio.html

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  15. Hi Archimago

    Many thanks for the great investigations and postings. May I ask: have you measured (or maybe just "tried anyway") the analogue audio out of the Pi 3 via the 3.5mm stereo audio socket?
    I wonder how that compares with, say, a standard SlimDevices/Logitech Squeezebox Classic?

    Not needing the "DAC HAT", if it's any good it might make a VERY cheap replacement for the now-no-longer-in-production Squeezeboxes!

    Thanks.

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  16. Archimago,

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

    Thanks for your work!

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    1. I'll have a look and post on this Josh...

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  17. Fantastic stuff Archimago! Thanks to your blog, I am now enjoying the pi3 and hifiberry dac. Some day I will compare it to my Classe CP800 DAC that is boxed up in the basement right now, but from what I am hearing so far and the measurements you shared, the law of diminishing returns for DACs has started to kick in very early these days. I cannot believe people are still spending $20K plus on DACs/streamers.

    Thank you and please keep up your good work.

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  18. I think that there is still a switching power supply present in the system when you are measuring with battery power. There is most likely one Li Ion cell in that Duracell and a boost converter that transforms voltage to 5 volts (Measure if there is any ripple with a constant resistive load?). The point you make on efficiency of linear regulation is valid only when the difference of input and output voltage is great. On the other hand switching power supply's efficiency is dependent on the load and not constant. There is always an efficiency curve for each switching supply, a simple number will not be enough. There might be situations where linear regulation ends up with a greater efficiency on a small load. Well, with battery powered applications it might never be the case, as the input voltage varies, and more headroom for voltage drop is needed.

    I'd test with a sealed lead acid battery and a linear regulator behind it. Then Any switching supply would be eliminated, if none was present on the board itself. There might still be no difference :)

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  19. Hello! Can you make measurements of Raspberry Pi3 + IQaudIO Pi DAC Pro?

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  20. Watch this ladies & gents!
    BRYSTON Audio from Canada are selling our Hifiberry for approx 1300 canadian dollars! ;-)

    http://bryston.com/products/digital_audio/BDP-Pi.html

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  21. Hi Archimago,

    You mentioned The Hans Beekhuyzen Channel and his testing equipment. I think he never use it or he don't know how. He mentioned in some video that soldering is hard for him and I don't wonder, he is just a journalist. He even deleted my comment when I did not agree with him about raspberry Pi3 usb audio. :D Maybe Hifiberry pays him? But I have to say that I sometimes agree with him. I use testing equipment and high-end audio gear with my ears and I must say that cheap smpsu sounds different than low noise lpsu.

    Best Regards,

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  22. If you ever get your hands on cheapo HiFiBerry DAC+ Zero, I'll be very curious about its sound quality and comparison to DAC+ Pro.

    Thanks for what you are doing :)

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    1. Unfortunately I can't edit my comment. Got an idea in the meantime. You still probably have Raspberry Pi 3 with HiFiBerry DAC+ Pro, Odroid C2 and E-MU 0404. Since lastly you can sometimes catch used 0404 for cheap, it would be interesting to compare HiFiBerry DAC+ Pro with 0404 connected to Raspberry Pi 3 (it would also be a test of USB Bus vs I2S). Eventually, if USB Bus is an issue, 0404 connected to Odroid vs connected to RaspberryPi could show how big a difference it may be (and if one is any better for use with USB DACs).

      Keep the good work. Thanks.

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    2. Ok, found that you've already made USB issue verification :)
      And HiFiBerry DAC+ Pro vs E-MU 0404 could also be somewhat compared with your older articles. All this is saying to me is if I chose Raspbery Pi or Odroid as streaming device and any of mentioned DACs, I'll be happy with the sound that I get. Thank you.

      If you every get your hands on HiFiBerry DAC+ Zero, please make those measurements and listen to it. Who knows - maybe HiFiBerry or some canadian shop selling those would be willing to send you one for tests.

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  23. Just bought two HiFiBerry DAC+ Pro, they sound very good.
    There is only one problem when the clocking is changed from 44.1khz to 48kHz, there is an audible glitch for at least half a second. I'm running LMS and PicorePlayer on the Rpi 3.

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  24. In the end, is there any real audible difference between DAC+ standard and DAC+ Pro? Do those oscillators make an audible difference?

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