HiFiBerry Digi2 Pro Impressions

Discussion in 'Digital: DACs, USB converters, decrapifiers' started by Woland, Mar 30, 2021.

  1. Woland

    Woland Almost "Made"

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    This is the updated Digi + Pro, now called Digi2 Pro ($44.90 ex shipping).

    I bought it after reading the SBAF discussions on the Pi2AES ($149) , and figuring my Gungnir Multibit doesn't connect to any of it's fancy outputs. The Digi+ Pro outputs digital via Optical, RCA or BNC so it's a good match. I'm hoping it will improve audio quality by reducing jitter.

    I was upgrading my Pifi Digi+ ($17.50 on AliExpress including case) sitting on top of a Raspberry Pi 3 and running Volumio.


    HiFiBerry's Blog post for launch says:

    The Digi2 Pro is slightly smaller than the PiFi Digi+, and with a different arrangement of outputs. I will use the same case, just omitting the faceplace on the output side.

    [​IMG]
    [​IMG]
    [​IMG]

    The Digi2 Pro worked fine with my existing Volumio I2S settings. I then changed the I2S the setting from Digi to Digi+, which I'm guessing enables the clock switching.


    How does it sound? On powerup I was immediately struck by the placement of instruments and the expansive soundstage, and the crispness of cymbals... It's mandatory to write that kind of text, right? Honestly, it sounds about the same, maybe a slight improvement in spaciousness. I think that is as much as can be expected for digital source changes. Maybe I'll notice more in time.

    I removed the jumper which is described for earlier models as a way to get full galvanic isolation. With the jumper, there is a high-resistance ground connection to make sure the receiving side isn't on a floating potential (which creates problems with the transformer shielding). Removing the jumper might have helped.

    I'm currently outputting via RCA but will likely grab a BNC cable in future.

    I probably won't use the DSP add-in board functionality. DSP functionality is already available in Volumio via BruteFIR, and it seems to do room correction filters quite well without putting much load on the processors.


    So for my specific setup, the upgrade benefits were:

    * Supporting the designer. I'm assuming the PiFi is a knockoff of HifiBerry's design.
    * Dual clocks
    * Better components, hopefully
    * Galvanic isolation
    * BNC
    * HAT passthrough. I could attach a screen or other expansion in future.
    * Cooler-looking, black circuit board
    * Plausibly better audio

    And the costs were:

    * The expense
    * 5 minute install
    * This post.
     
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    Last edited: May 15, 2021
  2. Huhnkopf

    Huhnkopf Friend

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    The PI2AES has BNC, Coax and optical though.


    [​IMG]
     
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  3. purr1n

    purr1n Building Magnis part time because it's peaceful.

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    ???, ^ this above, and I'm looking at the back of my Gungnir MB and pi2AES (using BNC coax) and scratching my head.
     
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  4. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    I just like that he called us fancy!
     
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  5. Woland

    Woland Almost "Made"

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    The PI2AES is listed as having BNC AES (not BNC SPDIF like Gungnir).

    You're paying around 4x the price to get access to supported I2C and AES with the Pi2AES. How does it make any sense paying that price if you can't access those?
     
    Last edited: Mar 31, 2021
  6. Woland

    Woland Almost "Made"

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    That is a big part of the PI2AES proposition right: support for AES and I2S? Having AES in the name seems like a pretty strong hint.
     
    Last edited: Mar 31, 2021
  7. Merrick

    Merrick A lidless ear

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    You’re overthinking this. Basically, single ended AES, whether carried over a BNC or RCA cable, is SPDIF. Pi2AES boards work perfectly with DACs that have only SPDIF connectors.

    I had a Hifiberry Pi hat before and it does sound good, but Pi2AES has a higher level of refinement. Whether this is worth the higher price can only be determined by using your ears. I’d say the Hifiberry is a great option for people who want to just get out of bad (read: most) USB audio transmission. The Pi2AES is for people who want superior audio quality in their digital chains without breaking the bank.
     
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  8. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    So this comes up a lot, what is the difference between single ended AES and SPDIF. Single ended AES is carried by a BNC connector over a 75 ohm impedance cable at a voltage level of ~1V. SPDIF uses an RCA connector which has no impedance control, and a coax cable, which may or may not be impedance controlled, at a voltage level of ~ 0.5V. This means that AES can drive longer cables such as found in a studio. For typical consumer use there is no difference between them and the most important factor is the clock generation on the source (PI2AES or digi).

    I will have to check to see if anyone has done any jitter testing of the new Digi board and what the results were.

    At the end of the day you made a decision based on some faulty information, however the value judgment that you are making may very well be a good one. Depending on the cost of the rest of your system saving the $100 between the two boards could allow you to improve some other part of the chain.
     
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  9. Merrick

    Merrick A lidless ear

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    Thank you for the clarification!
     
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  10. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    You are welcome. I should probably copy that and save it on my PC so I can paste it in anytime I need it!
     
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  11. Woland

    Woland Almost "Made"

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    Thanks for the contributions! It's good to know that AES can work on a SPDIF BNC input, and I wish that was indicated on the PI2AES description. However, for my setup it still feels like putting high-octane fuel into a mid-range car.

    After a bit more listening, I do feel there's an audible improvement from the Digi2 Pro. The improvement is a very small one, and I am happy to have made the switch from earlier sources of PiFi / Chromecast Audio with Optical SPDIF / USB. If I was going to spend another $200 or so to improve audio, it wouldn't be a further digital source upgrade.
     
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    Last edited: Mar 31, 2021
  12. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    One last note for those reading this thread at a later time, The PI2AES also outputs spdif on the RCA connector as described in the board documentation. The description was not incorrect simply not understood.
     
  13. Woland

    Woland Almost "Made"

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    BNC is fancy?? Now I'm scratching my head.

    Anyway, this thread has been hijacked.. It's about the HiFiberry and its three very ordinary outputs! There are multiple other threads on PI2AES.
     
    Last edited: Apr 1, 2021
  14. loadexfa

    loadexfa Friend

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    As long as you enjoy it, that’s all that matters.

    Feel free to sign up for the Pi2AES loaner if you’re interested. I found it wasn’t overkill for a Gungnir and made a noticeable difference. I even heard a difference going from rca to bnc into the Gungnir. The loaner would also allow you to add a comparison to this thread which would be a nice addition.
     
  15. purr1n

    purr1n Building Magnis part time because it's peaceful.

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    Yes, BNC is fancy. Whenever possible, I prefer BNC because the connector is much more secure than RCA. Some people feel that BNC > RCA SPDIF sounds a bit better. Digi2 doesn't do BNC, unless you DIY it, which voids the warranty.

    I usually use the AES output from sources to Gungnir via a 110-ohm to 75-ohm AES3 to BNC transformer with a short run on the coaxial side. Now this I do think sounds better than BNC/RCA. The only reason I'm not running it now is because it's packed away somewhere and I can't find it.
     
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  16. Woland

    Woland Almost "Made"

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    I'm guessing a decent BNC connector is just too expensive to build into a $50 board, especially when few buyers would use it. They did sell me a BNC connector with the board for another $8 or so. BNC seems to be highly regarded on the Gungnir.
     
  17. hifiandrun

    hifiandrun Almost "Made"

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    Please don't feel this way. ^ This is the SBAF not any other forums. The people around here have knowledge, experiences, and ears. And people here are cool, direct, and honest.

    Many people have tried multiple raspberry Pi digital hats and even modified and tried to improve their hats and reported the results with comparisons. To my understanding, the most significant difference between the Hifiberry Digi+ 2 pro and the PI2AES is not the number or type of the outputs, but the design philosophy. HiFiberry is cheaper and simpler aimed to gain popularity, good enough for most users as it could easily sounded better than the spdif output from most mid-fi CD players. In contrast, the Pi2AES aimed to get the highest sound quality possible out of the digital format of music.

    First of all, although it is good to see that Digi+ 2Pro used dual clocks as you've highlighted (one for 44.1k based frequencies, and one for 48k based), I believe that the dual clocks on the Pi2AES have way better specifications (femto grade instead of pico grade) and an audiophile-approved sound quality. Second, the regulated DC power supply for the clocks and the I2S-spdif transceiver chip (wm8804 or wm8805) is also one of the lowest noise type available on the market. The noise of the DC power supply affects the sound. Third, you've mentioned galvanic isolation, a hot word however is one of the misused terms in the topics of digital audio conversion. If you meant the SPDIF signal transformer, the Pi2AES uses a couple of Murata DA101, also a DIY community approved high performance part. I don't know what is on the Hifiberry Digi+ 2pro. Also I could be wrong, but I think that the Pi2AES also uses galvanic isolation chip(s) between the board signals and the I2S output (using the HDMI format port). . see Michael's comments below.

    Thus, this may be a better board in the HiFiBerry product line up, which is great. But I doubt it would deserve a new thread on SBAF because I don't see any design and technical advancement from the Digi+ 2Pro yet.
     
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    Last edited: Apr 1, 2021
  18. Michael Kelly

    Michael Kelly MOT: Pi 2 Design

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    There is no isolation between the i2s signals and the expansion header, just a simple buffer. For the i2s over HDMI the signals are converted to differential lvds twisted pair and sent over the HDMI connection. Again though, there is no isolation as they all share a common ground return. This is very standard, and the jitter performance speaks for itself.
     
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  19. Woland

    Woland Almost "Made"

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    Thank you! I really appreciate your kind words and taking the time on that response. I've had mixed experiences on SBAF, with some being extremely positive, and which have caused me to sign up as a contributor and explore the archives.

    Stepping back a little, my interest in sources arose because of an excellent youtube video by GoldenSound. From my recollection, he discusses jitter, and how differences in digital timing could work their way through to the audio in a measureable way, and argues that human hearing is sensitive to those differences. He also identified that some DACs would fix this via PLL, so the clock was less important. He was very positive about the Pi2AES performance but didn't discuss other pi devices. Reading a bit more, I got an appreciation of how BNC might have better impedance matching resulting in reduced jitter generation between the source and DAC.

    The above moved digital sources from my mental 'highly sceptical' list (cables, anti-vibration mounts, USB regenerators etc) into my 'plausibly important list' (tubes, power regeneration, balanced DACs and Amps etc). It still seemed likely that the source would make little difference to my specific setup because one of the Gungnir's headline features is its clock regeneration.

    What I read about the Pi2AES suggests it is meticulously engineered. But it also seems overkill to address jitter in my system, requiring additional case, power supply and targetting a host of other connection formats. I preferred the design philosophy of the Digi boards which is showcased by articles that provide a reasoned and sceptical view of linear power supplies, I2S etc and result in a product that seemed likely to give a meaningful improvement to jitter. The tone of the Digi forums suggests someone who has an engineering perspective a bit like Michael Kelly, but is maybe years down the line in terms of product development, distribution and customer+competitor frustration. There's an overlap in components, like the wm8804.

    I recall the early discussions from Michael on SBAF were actually about making a better Digi-like product. Digi have also made a better product, and it is around $50 without requiring a new case and power supply. So I decided to give it a try.

    My subjective experience is that the upgrade to the Digi2 Pro (with generic power supply and RCA SPDIF) makes a small but unambigously positive audible difference to the Gungnir, and is above the experience of PiFi and Chromecast Audio. Source refinement is proving a better audio direction than my experience of dabbling in exotic and somewhat expensive tubes. I hope someone does an objective comparison of jitter or other quality metrics on the alternatives. In the meantime, I'm added to the queue for the SBAF PI2AES and look forward to giving a subjective comparison.
     
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    Last edited: Apr 1, 2021
  20. Woland

    Woland Almost "Made"

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    My OFC BNC cable arrived, so I have the Digi2 Pro triple-mated into the Gungnir Multibit. That's SPDIF via Optical, fancy BNC and boring RCA.

    After a bit of switching, I don't notice any clear difference between the resulting audio.

    Maybe, for a short section of one test recording I notice a little less directional focus via optical than via the other two.

    I can't switch fast and blind because Gungnir Multibit has a fixed rotation of inputs: usb (unused), optical, rca, BNC. So there might be expectation bias coming into play as I expected the optical to sound worse and was hopeful the BNC would sound like the soundtrack to the gates of heaven opening.
     
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