PREVIEW / SET-UP: Raspberry Pi 3 Model B & HiFiBerry DAC+ Pro

As you know from discussions a few months ago, I'm a fan of the credit-card sized SBCs (Single Board Computers). I've already spent time discussing the inexpensive but powerful ODROID-C2 and the setup of this computer as a streamer to my TEAC UD-501 USB DAC using Volumio 2 including the excellent measurements one can get with this combination.

Today, let's talk about this very affordable combination:

Pi 3 Model B (left), HiFiBerry DAC+ Pro (right) boards.

What you see above are 3 items:
- Raspberry Pi 3 Model B - SBC computer, <US$40
- HiFiBerry DAC+ Pro - DAC "HAT" (Hardware Attached on Top) <US$60
- Inexpensive Raspberry Pi case with allowance for the HAT - ~US$10 - red to remind me I have a Raspberry in there :-) - here's a black version

Basically, we have here the hardware for a high-resolution audio streamer with integrated DAC for around the US$110 price point before taxes and shipping.

Assembled:

With those 3 components, once attached with an appropriate micro-USB cable to an AC adapter for power and a home network, what we have is a wireless audio streamer capable of hi-res (up to 24/192) with potentially excellent sound quality. All while sipping less than 5W of power especially since we're not using the HDMI video output at all when running "headless" (of course, unlike much more expensive devices like the MicroRendu, this device can be connected to video if you so choose). This kind of system could easily replace one of the Squeezebox devices if you run the piCorePlayer software. So long as one isn't technophobic, one should be able to put the hardware and install the software in a couple of hours (you'll need a microSD card for the OS/storage of course, an inexpensive 8GB card like this will do if you're just going to install something like Volumio/RuneAudio as discussed below without much media content)...

By the way, you might want to put a small VGA memory chip heatsink on the Broadcom CPU as it can get warm as I did above.

The Raspberry Pi 3 is currently the newest and most capable board in the family of Pi computers. It is based on a Broadcom BCM2837 quad 64-bit ARM Cortex-A53 processor running at 1.2GHz, 1GB DDR2 RAM, and VideoCore IV graphics processor (1080P resolution only). It has great wireless convenience with both WiFi 802.11n and Bluetooth 4.1 built in. Only 100Mbps ethernet though. Comparatively, the ODROID-C2 has a faster processor (2GHz quad Cortex-A53), more RAM (2GB DDR3), Gigabit ethernet and a much more capable video processor with HDMI 2.0, 4K/60fps output and hardware decoding of HEVC/H.265 including 10-bit video files (this actually makes the hardware decode capabilities better than an Intel SkyLake!). Of course hardware is half of what makes a good system. The software support for the Pi is second to none with many more developers and access to the latest Linux kernel for features and driver support. (I assume the Hardkernel/ODROID folks are making headway into Linux kernel 4.4 by now with Amlogic's recent update...) Furthermore, those wireless options for the Pi 3 are really convenient for lower data rate communications. Whereas the ODROID-C2 is great for video streaming, the Pi 3's specs really lend themselves to audio which is exactly what I'm aiming for here.

For the Raspberry Pi crowd, I think the HiFiBerry DAC products really need no introduction. I have not seen any numbers but given the apparent popularity on forums, I assume these are the "audiophile" boards for the Pi which others would be compared to (see this list for many others). Despite the low cost, I chose the "highest end" version of the DAC board they offer - the DAC+ Pro. Let's have a closer look at the DAC board:

As you can see, this board is based on the TI/Burr-Brown PCM5122 DAC chip at its heart. This chip is capable of operating up to 32/384 (the board itself goes up to 24/192) with a rated SNR of 112dB which is of course excellent but the actual performance depends on more than just the DAC chip. You also see a couple of Fox Electronics XpressO oscillators to the right for 44.1kHz and 48kHz families of samplerates. There were no detailed markings on these. In any even, "typical phase jitter" on these chips are low especially given the relatively slow samplerates used in audio applications measured on the order of a few hundred femtoseconds at most - more than enough accuracy for human ear/brain processing, right?!

Over the years, I've heard discussions about the I2S interface and how folks feel this is "the best" interface. Obviously for this HAT board, it's connected to the Pi motherboard through the 40-pin GPIO and communications are through I2S. Remember that I2S (Integrated Interchip Sound) is an old standard dating originally from the mid 1980's as a simple way to transmit stereo audio data using 3 lines (the digital data line, word select for right/left channels, and the serial clock line)... Usually this happens between the transport reading and decoding the data typically from a disk (CD) and then transmitted to the DAC chip(s) inside the box. You can read more about the interface from this 1996 updated document. As noted above, the clock line is separate and allows more accuracy (lower jitter) when the system master is of higher quality. Since jitter is a function of the accuracy of the master clock, I2S can still be vulnerable to jitter, so there's no reason to exalt the interface as if this in itself is a predictor of sound quality... Since it has been shown that the Pi isn't the best in terms of clock jitter (see discussions here), the HiFiBerry DAC+ Pro with its dual oscillators acting as master clock should be an improvement. Remember that the I2S interface was designed as an internal direct interface to the DAC chip, not meant as an external interface like S/PDIF or USB to span the distances between different boxes. As I discussed back in August, sound quality is really about the quality of the DAC itself and unless someone can prove that there's an issue with noise or jitter, digital audio data transport across an interface like asynchronous USB is robust and "audible" differences are as far as I'm concerned more imaginary/placebo/biased than based in reality when purely subjective reviewers claim "obvious" differences between what should be competent gear.

By the way, HiFiBerry describes the DAC+ Pro as "hackable". You can see the traces for external 5V power supply (top left), phono jack (bottom left to the RCA jacks), and I2S header for an external DAC labelled P4 (top right) - a bit of soldering needed of course.

On the software side, initially I tried running RuneAudio for DLNA/UPnP audio streaming. Unfortunately, it didn't seem to detect the HiFiBerry DAC+ Pro audio output by default. As such, I went back to the latest Volumio 2 (0.979, dated 2016-08-20) which detected the audio card and settings right off the bat. Another impressive feature with Volumio recently is that a "Volumio" hotspot will be created so you can log into the machine (ie. connect to that hotspot with a cell phone) and from there instruct it to log into your home WiFi SSID and enter the password! Do a restart after this and the machine should automatically log on to your home wireless network. Great way to install everything completely wirelessly. Having said this, unless you have a really strong signal, I feel WiFi is fine for standard 16/44, but too unreliable for high-resolution 24/96+.

Just to make sure the driver is recognizing the HiFiBerry DAC+ Pro running the clock oscillators, you can PuTTY into Volumio (ID & Password = "volumio"). Issue the command "aplay -l" to list audio devices.

No question the great thing about the Raspberry Pi is again the broad range of software options. Check out Archphile for a solid MPD distribution with the lowest CPU/RAM footprint, piCorePlayer for those running Logitech Media Server rather than DLNA/UPnP, and of course Roon Bridge for ARM if you're a Roon user. I see there are discussions on using the Pi for HQPlayer's NAA as well which I have not explored at all. With open source software, you're of course free to tinker and add to the community efforts as well.

Streaming audio to the Pi/DAC+ Pro is easy and essentially the same process as previously described using JRiver (I'm running version 22 these days) on my Windows Server 2012 R2 PC.

Beyond embedded applications like as a streaming device, the little red Pi 3 can act as a desktop machine:

Little red Raspberry Pi 3 running Raspbian OS dwarfed by 55" LG 55LW5600 TV...

It'll do the job as a simple web browser, run business apps like LibreOffice, basic games like the pre-installed Minecraft (without high draw distance)... But let's face it, the speed of a low power ARM CPU like this will leave most of us somewhat underwhelmed for day-to-day tasks; not to take away of course from just how much it can do, which is quite amazing!

Finally, just a few words on how the DAC output sounds so far streaming off Volumio 2... Very clean. This is running off my little switching power supply (the same Fujifilm branded USB power supply used in my ODROID-C2 tests). No issues with audible interference or noise. I suppose you could buy a metal case like this one if you're worried and think shielding is needed (might affect WiFi and Bluetooth). Miles Davis' 'Round About Midnight (2005 Legacy Edition Remaster, DR12) needs no introduction as the first of Davis' Columbia releases back in 1957. With fantastic synergy - especially Coltrane on sax and Garland on piano, it's a classic... Playback with the Pi 3/DAC+ Pro on my main system (Emotiva XSP-1 preamp, XPA-2L monoblocks, Paradigm Signature S8 v3 fronts, SUB 1 subwoofer) sounds precise and accurate. No evidence of tonal coloration. Temporal resolution on percussion appears to be very tight with excellent subtlety. Soundstage is wide with great image stability again suggesting excellent time precision and channel balance. I don't believe I'd be able to differentiate this from my much more expensive TEAC UD-501 DAC or Logitech Transporter, both of which have the upper hand using balanced XLR cabling in my current set-up. Likewise, other CDs sounding excellent include the string work on the new Mark Knopfler & Evelyn Glenn's Altamira (2016, DR13, nice "body" to the instruments), I caught up on the vocal works of Chet Baker on Chet Baker Sings (1953-1962) (3 CDs, I'm a bit disappointed by the use of more dynamic compression on CDs 2 and 3) and Willie Nelson's recent Summertime (2016, DR10) if you don't mind the Willie-does-Gershwin vocals :-). The "synthetically clean" production sheen in pop songs like the heart-breaking tune "The A Team" from Ed Sheeran's + (2011) was easily heard.

I suspect you're not here to read about my testimony of sound quality :-)... Rest assured, next time, let's have a look at the objective results and see if my subjective impressions are borne out by the measurements.

Have a great week and enjoy the music everyone!

Addendum:
By the way folks, there's still a bug with Volumio in that if you rename the device, do not use space and symbols other than '-'. For example, I use "Volumio-RPi3" for this streamer device and that works. But don't try "Volumio (RPi3)", sometimes I've notice doing this will take the device off-line and you might need to reflash the microSD.

*** Results of measurements are up. ***