Connect digital output in fixed volume mode is not bit-perfect as discussed here
. There is a simple limiter applied with a maximum gain decrease of just under 1dB. This cannot be defeated in fixed volume mode.
However, in variable volume mode the maximum limiter gain becomes less as the volume slider is decreased from maximum. The limiting disappears completely after 13 taps on the slider. This is shown in this
The associated volume decrease in the signal is shown here
. It is interesting to note that as the volume slider is moved back from maximum, the rate of volume decrease becomes larger at the same 13 tap point. I haven't gone beyond 20 taps to see if there are further changes in volume sensitivity.
What are the implications? Prior to version 6 of the software, fixed volume mode provided the cleanest audio path (bit-perfect), but this is now not the case. The cleanest audio path is now obtained by using variable output and setting the volume slider to 13 or more taps less than the maximum. It is not
bit-perfect, since the volume has been decreased, but the decrease is at least uniform. Since Sonos use a 24-bit volume control, this volume decrease does not lose any information or cause any audio artifacts (except at very low volume) providing you feed a 24-bit DAC. An older 16-bit DAC will lose information at all volumes.
The upside is the ability to control the Connect volume using the app. This is also a downside because there will now be two volume controls for this room - the Connect and your amp. This is probably a small issue.
Another implication is for the speculation that other Sonos gear is affected by this limiter. Since it appears that the limiter is downstream of the volume control, it is now most likely that any limiting only happens at relatively high volumes, which is probably a good thing :)