As the title says, the Sonos Port isn't bit perfect. What's the big deal? For many Sonos users this is a non-issue because they are streaming from very lossy services such as Apple Music or Pandora. However, for people who care about sound quality, this is a big deal because the music sent though the Sonos Port has been digitally processed before anyone gets to hear it. Before digging in further, let's take a step back and define some terms and explain some additional details.
Sonos is mostly known for its speakers, but the company has also always offered a component with built-in digital to analog conversion and a digital audio output. The Sonos Connect was the previous generation of said component, and the Sonos Port is the current version. I have both components in my listening room, connected to the same system for testing.
These Sonos components with digital outputs have always been terrific for those of use seeking high quality audio because we connect the digital output to the DAC of our choice and send the signal on to our refined audio systems. Many audiophiles I know do this as well as tons of custom installers around the globe have connected these Sonos components to outboard digital to analog converters. The reasons for this are that Sonos has the most content (think the regular services, but also Pandora and SiriusXM) and the products work very well. Connecting the Sonos Port to an outboard DAC can elevate the audio performance to another level because the internal DAC is somewhat limited.
What is bit perfect and why should I care? In the simplest terms, bit perfect means that the audio hasn't been changed. The music sent into the component is the exact same music that comes out of the component. If you care about high quality, getting the lossless streaming you're paying for from Qobuz, Tidal, Amazon Music, etc... or about playing a local library of ripped CDs without unknown signal processing taking place, then you should care about bit perfect because without it you have no idea what's happening to your audio. If this isn't a concern for you, no worries.
The Sonos Connect and the Sonos Port both have settings that are supposed to enable digital audio to traverse through the units without any digital signal processing. The Connect works as it should and outputs bit perfect audio without an issue. The Port on the other hand, can't output audio without some type of signal processing taking place inside the unit.
To test this, I setup both the Connect and the Port identically. Both units were set "Fixed" Line-Out Level. Even though the terminology suggests this line out is the analog output, it also effects the digital output, as seen in my testing. Fixing the output level just sets the volume to 100% and prevents the Sonos from reducing bits to reduce the volume of the music. When this is set, the EQ can't be adjusted. I looked through all the other settings and made sure there wasn't enabled anything that could change the sound. Both units were identical.
Keep in mind that the Sonos S1 app is used to configure the Connect and the new Sonos app is used to configure the Port. This shouldn't be an issue because the settings are the same no matter which app sets them and the audio being sent to the units doesn't route through the iOS app or desktop apps.
Once the units were setup, I use the following testing methodology to determine that the Port wasn't outputting bit perfect audio.
I use a Berkeley Audio Design Alpha DAC Reference Series 3 that identifies and decodes HDCD on all sample rates. When an unaltered HDCD file is played, the HDCD indicator on the DAC is illuminated. The HDCD flag is on the 16 bit for CD files and the 24th bit for high resolution files. Any alteration, DSP, volume leveling, etc... changes this least significant bit and won't enable the HDCD indicator to illuminate. Given the Sonos units only support 16 bit / 44.1 kHz audio, I only tested this resolution. That's the hardware piece.
With respect to source files, here's what I do.
I have a list of roughly ten known HDCD albums (although I could use more if needed). Many of these albums were only released as HDCD encoded CDs/files. There is no alternate lossless version. For example, Reference Recordings only releases CDs that are HDCD encoded.
I set a baseline by playing my own local copy of the albums and make sure the HDCD indicator illuminates.
I used the Sonos applications on iOS and macOS for playback during this test.
Through the Sonos apps and the Sonos Connect, I streamed my known HDCD releases first from my local ripped CD copy, then through Qobuz, then through Tidal, and finally through Amazon Music HD. I wanted to use my local file baseline, then a few streaming service baselines.
Then I tested the Sonos Port using the same procedure. Local files followed by streamed versions from the lossless services.
Absolutely there are possible holes in my methodology, but I believe I've minimized them as much as possible. I also reached out to Sonos in an effort to check my methodology and show them the results, but I didn't receive a response.
Using the Sonos Connect, everything I sent from my locally stored ripped CD and all the streaming services was bit perfect. As long as the Connect was setup correctly, I couldn't get it to fail. Bit perfect every time.
Using he Sonos Port, I couldn't get it to pass a bit perfect audio stream no matter what I did. In other words, it failed every test. Local stored ripped CDs and streamed music from all the lossless services were all altered between the time they entered the Sonos Port's ethernet input and the time they extend the Port's coaxial digital output.
Take this for what it's worth. Some people won't care, while others will want to look for better solutions. I highly recommend the Bluesound Node 2i as a replacement for the Sonos Port. The Bluesound ecosystem doesn't have Pandora or SiriusXM, but for most people it has everything they need and it's bit perfect with local and streamed content in all supported resolutions up through 24/192.
Perhaps Sonos will explain what digital signal processing is taking place inside the Port or even issue an update that enables users to turn off this DSP and output bit perfect audio. Until such time, the Port is a hard pass for me.