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Peter Mc
Peter Mc
August 23, 2016
Question

Connect no longer bit-perfect?

  • August 23, 2016
  • 450 replies
  • 29769 views
It looks like the Connect is no longer bit-perfect. Here's my evidence: let's discuss this.

First, I constructed a wav file of pink noise with amplitude ramping up from zero to digital max and back to zero.
I play this through my Connect and record the SPDIF output from the coax output into my PC.
The recording uses a Scarlett 8i6 audio interface set to use the Connect as master clock.
I record into a DAW (Sonar) multiple times - all instances are identical.
However, this recorded signal is not quite the same as the original wav file - it can be up to -21dB different.
See https://www.dropbox.com/s/t8od479xo9hi5el/connect_diff.PNG?dl=1
Note the expanded scale on the difference (third) track.

It looks like the difference gets larger when the signal is larger. To confirm this, I import the
original and difference files into Matlab and plot the raw data (difference vs original). There is clearly audio compression
happening here. See https://www.dropbox.com/s/p1yq6wcqafvnhaj/diff_vs_orig.png?dl=1
The scale is such that digital maximum is 1.

There also appears to be a slight bias when the waveform is negative and the signal is below the
compression threshold. See an expanded version of the previous plot
https://www.dropbox.com/s/9001tl9mkle4wly/diff_vs_orig_zoom.png?dl=1

Happy to answer questions about the method and conclusions.

Cheers, Peter.

p.s. Volume is set to fixed - I haven't tried variable.
In a loopback test (8i6 out from DAW to 8i6 in, no Sonos gear involved), I get bit-perfect cancellation.
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      Peter Mc
      Peter McAuthor
      August 25, 2016
      Hi Kumar - here's my take. Others may like to chime in.

      1. There is 1dB of soft-knee compression applied. 1dB is an audible change in total volume (3dB is a doubling in power). A 1dB compression will be less audible as it only decreases the loud bits.
      2. There is a 1-bit bias on the negative part of the waveform. I really don't know whether this is audible. It will, however, apply a slight DC signal to the speakers.
      3. Volume normalization will alter the overall volume of all tracks to be more similar across tracks. For sequential tracks from an album that flow into each other this can cause an audible volume change.
      4. There is reputational danger for Sonos and the Connect because it can no longer be considered audiophile-quality gear. The original stereophile review of the Connect would have been scathing if these issues were happening back then.

      What can you/we do? Put pressure on Sonos to go back to disabling all signal processing when in fixed volume mode.
      The volume normalization problem can be overcome by removing the ITUNNORM tags from files. This is a hassle, and removes the option to use these tags when playing individual songs for a party etc.

      I think by far the best solution would be for Sonos to disable DSP for fixed volume, or add a switch so users can decide.

      As far as variable mode is concerned, I speculate that the same answers apply, but I haven't made any measurements in this mode.

      Cheers, Peter.
      "The presence of those seeking the truth is infinitely to be preferred to those who think they've found it" - Terry Pratchett
      ratty
      ratty
      August 26, 2016
      I think by far the best solution would be for Sonos to disable DSP for fixed volume, or add a switch so users can decide.
      Both.

      Fixed Volume should return to being guaranteed bit-perfect for players with a digital out.

      There should also be a normalisation defeat switch in room settings for all players. If loudness can be turned on and off I don't see why normalisation shouldn't too. (Objections from Sonos along the lines of "in the absence of normalisation tags a confused user wouldn't hear any difference" can surely be addressed.)
      ninjabob
      Chromatic Producer I
      August 26, 2016
      Does all this apply to REPLAYGAIN TRACK?

      Does removing this Tag return us back to Bit Perfect on the Connect?
      busy trying to edit the queue
      ratty
      ratty
      August 26, 2016
      Does all this apply to REPLAYGAIN TRACK?
      Yes, at present that can't be defeated at all on later models of CONNECT. See this thread: https://en.community.sonos.com/setting-up-sonos-228990/volume-normalization-processed-fixed-volume-output-6738413

      Does removing this Tag return us back to Bit Perfect on the Connect?

      Apparently not, to judge by Peter Mc's findings, at least on the later CONNECTs. It could be all bound up with the undefeatable volume normalisation issue.

      It would be interesting is someone could make comparable tests on ZP80 and ZP90.
      amun
      August 26, 2016
      Fixed Volume should return to being guaranteed bit-perfect for players with a digital out.

      Couldn't agree more...
      Majik
      Majik
      August 26, 2016
      Agreed here too.

      There needs to be a way where Connect users can guarantee bit-perfect signal from the digital outputs.

      As ratty suggests, I also think having the option to turn on/off volume normalisation is something that is long overdue. This way external DAC users can chose whether they want bit-perfect, or normalised. And, yes, this should be configurable per player.

      I also think that the "Album" type of volume normalisation should be the standard, instead of the "track" type if no user-selectable option is available.

      Cheers,

      Keith
      ninjabob
      Chromatic Producer I
      August 26, 2016
      I must be lucky - Hardware Version 1.1.16.4-2
      busy trying to edit the queue
      ratty
      ratty
      August 26, 2016
      I must be lucky - Hardware Version 1.1.16.4-2
      That's a ZP80 isn't it? Or just maybe a ZP90? Not a CONNECT surely.
      MikeV
      MikeV
      August 26, 2016
      My question is... how did Sonos allow the Connect to NOT become bit-perfect with the Fixed Volume setting?! Surely someone, somewhere would have realized that a change being made would affect the audio output, and that the Connect - the one Sonos device that has been reported as having bit-perfect digital output - would no longer be able to make that claim. If they decide that they want to still allow the level adjustment for the fixed volume setting, there should at least be the option to disable it, returning bit-perfect output for those that want it.

      On the other hand, many have wanted some kind of volume leveling in the speakers... and while Sonos has never said anything about it, it appears that they've been working on it.
      The S in IOT stands for Security.
        ninjabob
        Chromatic Producer I
        August 26, 2016
        I must be lucky - Hardware Version 1.1.16.4-2
        That's a ZP80 isn't it? Or just maybe a ZP90? Not a CONNECT surely.

        Yes ZP90 - but wasn't Connect just a rename rather than different device?
        busy trying to edit the queue
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