Sonos Port Sound Quality

When the Port came out, some reviews criticised the effect of the soft limiting on the digital output in variable volume mode. (Protection is required to avoid hard clipping on the S/PDIF.) This would be more pronounced at high volume levels.

However such reviews also said that either fixed output or analog/variable avoided such DSP and sounded okay. I use a few Ports, mainly for headphones, and choose the analog out into suitable head-amps or transmitters.

There is a danger when making such subjective comparisons of confirmation bias: you start thinking X sounds worse than Y, and from that point on X will always sound awful.

Back in 2011, the equivalent Connect was one of my first Sonos units, and it replaced a Marantz KI SACD player supplying Quad amplification with no heard difference in sound through downstream Harbeth speakers, via both analog and digital connections, because the Marantz also had digital inputs so that its DAC could be employed.

I would be very surprised if some years down the line Sonos went backwards in the sound quality that the next version of the Connect - the Port - could deliver. Not ever having heard the Port, I can't say more than that.

PS: Both my Connects continue to deliver the same performance today, as they did when new.

I connected my MacBook Pro with a Behringer UCA202 audio USB interface to the Port but did not perceive any better sound quality than AirPlay streaming on my vintage hifi nor on my Sonos speakers.

Presumably that’s to connect the MacBook to the Port’s Line-In, and comparing it to using Airplay over the network. The OP is talking about the Port’s outputs. 

I’m curious of if anyone has actually measured the sound quality. For example. Use the Line In or AirPlay a sine wave and observe the distortion on a scope, or a more complicated sweep test.

Has anyone else compared the sound quality of Spotify playback from a Port to any other solution like computers, other brands of streaming players.

I’m trying to separate the sound quality issue from any other feature or convenience.

“ratty” mentioned the soft limiting. I’m not sure why they feel the need to do that. The output levels from decoding streaming media is already known, and clipping would have been already handled by the provider, after all it’s digital content. It seems Sonos is touching bits they shouldn’t be, instead of accepting the outcome of decoding the streaming as is.

But this is not applicable to how you are using the Port, via analog outputs, and it therefore does not offer any explanation of what you seem to hearing as the sound being defective.

Last point first, with a variable volume -- which can go to 100% -- and EQ/loudness, it would be possible for samples to go over Full Scale and clip on the S/PDIF. Inter-sample peaks could also contribute. Soft-knee limiting to avoid this is normal, but the impression is that Sonos’ on the Port was somehow more aggressive than on Connect.

I made a few measurements on the S/PDIF early on, using single-frequency sine wave input. With a Full Scale (0dB) signal the effect of the limiting could be discerned above about 85% volume, using an analysis program, in the form of odd harmonics. This was of course based on an artificial stimulus, unlike real music.

Whether or not this limiting is still present in its original form on digital/variable output I have no idea. I’ll admit to confirmation bias of my own and thus prefer to use digital/fixed or analog/variable.

I mainly wish they gave an option to “harm no bits”, even if that isn’t the default. @ratty I appreciate the technical feedback, that is helpful to drive this discussion.

There is a “harm no bits” setting, just set volume to “Fixed”.  As to harming bits in the “Variable” volume setting?  Well, any setting which affects volume is by definition going to “harm bits”. 

@jgatie The problem I’m noticing is that the sound is still “off” even with fixed output.   This is in direct comparison to other digital playback devices using the same amp and speakers.

The thing is, we don’t know what they are doing with the “fixed level” output, it could just be a UI  change and not actually eliminate the soft compression the @ratty pointed out. So setting “fixed level” could just be setting the volume to 100% and disabling the volume slider and not actually instructing the DSP to change it’s behavior, thus allowing the soft limiter to remain active.

Technically, if you can adjust volume and/or equalization without harming any bits, by doing it in the analog domain, but that would add costs. Analog circuits like newer op-amps can easily have 120 Db dynamic range or more.

If anybody knows how to accurately test if bits are being harmed even in “fixed output”, that would be awesome, and I’d be happy to participate.