John
UPDATE 20th October: The LS50 Wireless II is the first third-party hi-fi product (outside of Sonos) to gain support for Tidal Connect — where the native Tidal app on any Android or iOS device behaves like Spotify Connect: fire up a song and use the device selector in the bottom left of the screen to select the LS50 Wireless II as the desired output device. The upshot for end-users is Tidal playback without the need for KEF Connect, Roon or UPnP. Just Tidal app and go, yo.
Our beginner’s video on the KEF LS50 Wireless II left one question unanswered: just how exactly did MQA work inside this streaming loudspeaker? The specifics matter to a small (but very vocal) percentage of interested parties. Were all of MQA’s unfolds handled by the primary loudspeaker, causing the maximum possible sample rate to be held captive by the speaker’s interlink; 24bit/192kHz for wired, 24bit/96kHz for wireless? Similarly: where was the rendering being done: in the primary loudspeaker or in both loudspeakers? To turn over that stone we’d need to first talk to MQA’s Bob Stuart and then to the LS50 Wireless II’s project lead Jack Oclee-Brown.
According to the man from KEF, MQA handling inside the LS50 Wireless II is a two-step process: the MQA stream – either 44.1kHz or 48kHz – arrives at the primary loudspeaker’s internal streaming processor. This is where the first unfold, should it exist, is executed. 44.1kHz is expanded to 88.2kHz or, more common, 48kHz to 96kHz. Step one is now complete.
For step two, the first-unfolded stream is sent internally to the primary loudspeaker’s ADi Sigma DSP chip where any further unfolds, should they exist, are executed and MQA deblur filtering applied.
But what about the secondary loudspeaker? Remember: the first-unfolded stream’s sample rate will always be at or below 96kHz, so it can traverse the LS50 Wireless II’s interlink without issue to arrive at the secondary loudspeaker’s ADi Sigma DSP chip, which then handles further unfolds (to 192kHz…to 384kHz) and applies MQA deblur filtering to the other channel’s data.
Let’s exemplify. Many of the David Bowie remasters reissued in 2015, 2016 and 2017 are streamable from Tidal and Qobuz as 24bit/192kHz studio masters. Unlike Qobuz, Tidal doesn’t send us a 24bit/192kHz file directly but a 24bit/48kHz MQA stream that has the potential to be unfolded twice: once to 24bit/96kHz and a second time to 24bit/192kHz; but only after the second channel’s datastream has traversed the KEF loudspeakers’ interlink.
When the Bowie MQA stream reaches the LS50 Wireless II, it is unfolded to 24bit/96kHz by the primary loudspeaker’s streaming processor before being handed off to the primary loudspeaker’s DSP chip internally and the secondary loudspeaker’s DSP chip via the interlink. Because the stream is still at 24bit/96kHz, it matters not if the interlink is wired or wireless. It is only once inside each loudspeaker’s DSP chip that the Bowie MQA stream is unfolded a second time to 24bit/192kHz and MQA’s DAC optimising filtering applied.
This two-chip approach is none too dissimilar to the way MQA is handled by AudioQuest’s DragonFly USB DACs where 1) the first unfold is executed by the host device (PC, Mac or streamer), 2) passed under the DragonFly’s USB1.1- and 96kHz-capped receiver chip ceiling for 3) any further unfolds and MQA filtering to be applied by the DAC circuitry itself.
In the LS50 Wireless II, the primary speaker’s streamer is analogous to the DragonFly’s host PC or Mac, the ADi Sigma chip to the ESS Sabre chip that sits on the other side of the DragonFy’s USB receiver chip and the loudspeaker interlink to the USB receiver chip.
For Qobuz, we would need the LS50 Wireless II’s wired interlink in place in order to stream the same Bowie in 24bit/192kHz. Alas, there is no way for Qobuz users running a DragonFly Red, Black or Cobalt to stream content beyond each USB receiver chip’s 24bit/96kHz glass ceiling.
Moreover, MQA’s audio origami and its two-step handling in the KEF LS50 Wireless II (and AudioQuest DragonFlys) permits streaming of 2L Recordings’ studio masters at their full 352.8kHz resolution. Readers are left to decide whether this is an uber-niche use case or a demonstration of what’s possible.
Before you answer, we might momentarily drop the hi-res fanaticism to ask just how much of our library, streamable or downloaded/ripped, sits above CD-quality’s 16bit/44.1kHz? Glossing over the answer risks putting the cart before the horse.
