Pi versus Pi
By Steve Graham
Raspberry Pi 4B with S/PDIF Out versus Raspberry Pi 4B with USB Out
Confession time. In responding to those kind enough to comment on part 3 of my Raspberry Pi series, I mentioned that I didn’t have a decent USB DAC for comparison. WRONG. It completely slipped my mind that my PS Audio DAC has a USB input. A cream pie in the face for me.
To satisfy my own curiosity and maybe mend a few fences with readers, I’ve run a quick comparison between two Raspberry Pis. One is a Pi 4B with the HiFi Berry Digi+ Pro HAT (the Pi used in the 3-part series), which sends digital out over S/PDIF coaxial. The second is a Pi 4B (no HAT) sending digital out over a USB connection. In both cases the digital signal was routed to my PS Audio DirectStream DAC. The PS DAC did dual duty in the three-part series, receiving data from both the Pi with HAT and my NAD 50.2 player. The DAC on the RPi board was not used.
I had a heck of a time getting the PS DAC to lock onto the USB signal. The USB output of the Pi was selected in the Squeeze Lite setup menu. I tried several methods to get it to lock, restarting PiCorePlayer, rebooting PiCorePlayer, even powering down and a cold restart. It was just a bit of a lottery whether or not the DAC would lock. I could never figure out why it would or would not lock, it just seemed random. Thinking it might be the DAC, I tried a Meridian Explorer 2 and it wasn’t any easier. The Meridian locks on to the USB out from my mid level HP laptop without issues. The PS Audio DAC locked, without issues, onto the coaxial S/PDIF signal from the Pi with the HiFi Berry HAT board.
Once locked, I compared the three tracks mentioned below, first on the USB-out Pi, then on the S/PDIF-out Pi.
Through the USB connection, this track sounded kind of catchy. The bass was a bit on the phat side, guitars had a nice ring to them and high frequency percussion didn’t “bite”. But the soundstage seemed a bit diffuse and the whole thing sounded sort of “mid-fi” and imprecise.
Through the S/PDIF connection, everything just snapped into a clearer focus. Bass was tighter, guitars and vocals clearer and highs had more precise detail without sounding harsh. The soundstage was more precisely rendered too.
Again, the USB connection was a letdown. The piano sounded sort of clangy on louder passages, the sax less liquid than I’ve heard it sound on my system, and the muted trumpet had less bite, brassiness and clarity. Percussion was less clear and the bass less distinct too.
Via S/PDIF the instruments sounded much more real. The was piano clearer and less strained, the sax smoother and at the same time more detailed. The trumpet was more believable, bass and percussion improved in the same way too. The recording acoustic was more apparent as well. There isn’t much of a continuous soundstage in this recording, but the trumpet was more precisely placed in the centre, and was as if it inhabited its own distinct pocket of air.
Same sort of deal here too. The S/PDIF connection had clearer vocals and the soundstage, even though an artificial recording studio construct, was more dimensional, with instruments more precisely placed and layered. Overall clarity and detail were better too.
Before anyone sends me a nastygram saying I must have done something wrong or I didn’t use power supply X, cable Y or software Z, I can only report on what I hear. I don’t mean to down play any of these improvements people make or say they don’t matter. I can only try so many options or variations on a reviewed item before I have to move on. My experience with USB may be atypical. If, in your system, USB is more enjoyable than S/PDIF, that’s fine, I’m not trying to negate your preference. It’s all about what sounds best to you. As always, performance is very system dependent. To summarize my experience: the fifty-seven bucks I paid for the S/PDIF HAT board was the best fifty-seven bucks I’ve ever spent in the service of musical enjoyment.
After finishing the Pi vs Pi comparison, I switched my system back to the NAD 50.2 and played the three test tracks again. There were improvements on many fronts over the Pi with the S/PDIF HAT board. However, these improvements were more subtle than the upgrade going from Pi with USB out to the Pi with S/PDIF out via the $57 HAT board.
The Raspberry Pi is an OK performing music server/streamer on its own, but, and it’s a big but, it makes a very much better server/streamer with the addition of an audio-grade HAT board.
I enjoy reading the review comments people leave. Thank you for taking the time to post them. My policy is to respond once and if the commenter wishes to follow–up, I give them the last word. If they ask a question on a second communication, I will endeavour to answer if possible or at least say I don’t know. I don’t think the comments space is a good place for ongoing sound quality discussions. Web forums better serve that purpose.
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