Answered

Playbar compression SBC FLAC

  • 6 April 2018
  • 9 replies
  • 241 views

Badge +1
Do we know whether the Playbar is streaming its input uncompressed?

If I connect an analogue source to a Connect, and have that music streamed uncompressed to, for example, a Play 1, then I can see that the bit rate is something like 1.5 Mbits/s, which is touch higher than a WAV file but close enough and therefore as expected.

I play my music using a Playbar (nothing to do with a TV, I just happen to have a spare Playbar). If I connect a digital music source via Toslink to a Playbar, and have that music streamed to a Play 1 then I can see a much lower bit rate: something like 400kbits/s.

The only explanations I could think of are:
i) The Playbar is compressing, lossy, (using SBC?).
ii) The Playbar is compressing, lossless, (using FLAC?) (to make transmissions to other speakers more efficient?)

Could anyone shed any light on this please?
icon

Best answer by Mike231 10 April 2018, 11:14

It seems Playbar does compress, and uses SBC. Sonos say:

"….the PLAYBAR compresses the audio to SBC and its bitrate is dynamic based on the number of components as well as the quality of the connection between said components. This would be equivalent to the Line-In compressed function…….[of Connect]"
View original

9 replies

How are you measuring the data rate, and what is the actual content? I have a slight suspicion that Sonos may do some simple run-length compression if it can.
Badge +1
Hi. The receiving Sonos speaker has wireless disabled and is cat 5 wired to a router which has a display showing its download bit rate. I'm confident that's a good measure.

The content is music which is non-compressed PCM stereo, delivered to the Playbar over optical.

If you mean https://en.wikipedia.org/wiki/Run-length_encoding, I can see why they would want to do that but it would be good to confirm it. RLE is fine but if Playbar is SBC compressing that would be nasty surprise.
Interesting. When I use a similar technique, but with a TV signal into PLAYBAR, the stream to the grouped player clocks a pretty constant 480kbps or thereabouts. If there is compression it can only be using a simple codec otherwise the latency would rise. I wonder whether they're using an ADPCM type approach.
Badge +1
Try as I might I cannot get the Playbar to dance any faster than c 0.5Mb/s.

If I plug any analogue source into my ADC then I should get at least a 16bit 44.1khz PCM stream, which should be c 1.4Mb/s. However, if I plug the optical output from my ADC into the Playbar and measure the bitrate at the receiving speaker it is only 0.5Mbs.

If I play a Quboz 16 44.1khz FLAC track on an Ipad, and stream that to an Airport Express, and take the digital output and plug it in the Playbar, again at the receiving speaker I get only 0.5Mbs.

I don't think Run Length Encoding can get 1.4Mb/s down to 0.5Mbs. Remember, when a Connect is broadcasting uncompressed the bitrate at the receiver is 1.4Mb/s. I wish RLE was that good but I don't think it is. If it were I would have thought Sonos would use it in the Connect as well.

Maybe Sonos is using FLAC to compress between Playbar and other speakers. But I doubt it; I don't think you'd consistently get that much compression and I think you would notice the latency. So does that leave the ugly SBC compression or am I missing something?
The evidence does suggest some type of content-independent compression. RLE would surely vary in bitrate (as indeed would FLAC).

There may or may not be subband division, but there clearly isn't any DCT/psycho-acoustic encoding as it would take too long. My betting is on some form of time-domain encoding such as differential PCM.

FWIW Bluetooth aptX employs ADPCM at 352k and one would be hard pressed to distinguish it from raw PCM. None of the artefacts typical of the psycho-acoustic encoders.

If Sonos isn't prepared to declare what's going on, one could always sniff the traffic and see if it can be interpreted.
Whatever the answer here, I wonder if the effect on audio quality will really be noticeable through Play:1s?

Picking up the theme from your other thread, I would still be tempted to abandon this approach. A subscription to Tidal or Deezer's lossless streaming service should cover off 90% of your friends' CDs??
Badge +1
Sonos are currently saying it's (completely) uncompressed. I really hope they are right but I cannot think how that could be the case.
Badge +1
Hi John. For various other reasons I won't bore you with I do need to know whether the Playbar is compressing even when the app is set to 'uncompressed'.
Badge +1
It seems Playbar does compress, and uses SBC. Sonos say:

"….the PLAYBAR compresses the audio to SBC and its bitrate is dynamic based on the number of components as well as the quality of the connection between said components. This would be equivalent to the Line-In compressed function…….[of Connect]"

Reply

    Cookie policy

    We use cookies to enhance and personalize your experience. If you accept you agree to our full cookie policy. Learn more about our cookies.

    Accept cookies Cookie settings