Sony WF-1000XM4 and Multipoint - Could Sony add it with firmware?

When Sony introduced the WF-1000XM4, many people believed they would support multipoint like their larger brother, the WH-1000XM4, but that did not turn out to be the case. Yes the earbuds can have multiple devices connected but not simultaneously. Even I was told by one source that there would be multipoint support, but I suspect there was a mistranslation of supporting multiple devices versus true multipoint support.

So why is there no multipoint support present in the WF-1000XM4? For a proper explanation, I suggest reading this post on Reddit by aborne25, since they are well versed in Bluetooth and its functionality. 

There are other earbud headsets that support multipoint, like the Jabre Elite 75t and the Technics EAH-AZ60. The Jabre earbuds use a Qualcomm QCC5126 Bluetooth SoC, so whatever methods Jabre used for multipoint connectivity could not be applied to the Sony since they moved away from Qualcomm.

On the other hand, the Technics use an Airoha AB1565M SoC. For those unfamiliar, Airoha is owned by Mediatek, so with multipoint working on an Airoha chipset, perhaps multipoint can bed added to the Mediatek chips used in the WF-1000XM4. The question now is, how different is the Mediatek MT2822 SoC to an Airoha chip like the AB1565?

Recall 2 posts, the Mediatek MT2811 post, and the Sony V1 post, in both those posts, I said that the MT2811 and MT2822 are just custom versions of the existing Airoha chips. I am aware a Linkedin post is not always reliable or correct, so there is one more piece of information from a FCC report. The upcoming new Sony X-Series wireless speakers, use a BMS002 Bluetooth module and this same module uses the MT2822 as its Bluetooth SoC.    

Okay, so assuming the MT2822 found in the WF-1000XM4 is just a rebranded/custom AB1568, how does it compare to the Airoha AB1565 chip found in the EAH-AZ60?

Technics EAH-AZ60 Bluetooth SoC

Well comparing both chipsets on Airoha's website, apart from the size of the chips (AB1568 - 5mm x 5mm; AB1565 - 4.6mm x 5.6mm),  I can only find 2 different features that the AB1568 has which the AB1565 lacks:

• Supports BC1.2 charger detection
• Precision voltage measurement for fuel gauge
  

Turning back to the BMS002, the FCC filing also provides us with an interesting piece of information, the specifications of the Bluetooth SoC (MT2822) and specifically the presence of "BC1.2 charger detection". Therefore it can be said, the MT2822 is either the AB1568 rebranded or a custom version of the chip. My guess is the custom work is more related to the AMP/DAC aspect of the chip and not the Bluetooth section. I will even go as far as to say that the Bluetooth part of the SoC is probably identical between the AB1565 and AB1568 chips. So whatever multipoint firmware Airoha/Mediatek have created for the AB1565, I am sure could be easily ported to the AB1568 and any Sony custom chips like the MT2822.

Just a side note, while looking for some more information about the AB1565, I found some discrepancies with what is written on the Technics website and the AB1565 specifications. Both this reddit post and this website report that the AB1565M does not support hybrid ANC and only has feedforward ANC.

But Technics own product page (see below) clearly states "combines Dual Hybrid feedforward and feedback noise cancelling".

So what gives? The FCC teardown photo shows the AB1565M as the Bluetooth chip in the EAH-AZ60, yet the specifications of the chip do not match up with the information on Technics' product page. So either the specifications on those websites are wrong or the product page is wrong. Having seen the FCC teardown photos, there are 2 NC microphones, feedforward and feedback, so I am sure dual hybrid ANC is present on the AZ60. So I am not sure why the discrepancy.

Turning back to the Bluetooth functionality, the Technics AZ60 received an update in early March which adds true multipoint connection with the LDAC codec.

The person using the LDAC function will be able to use the Multipoint function by turning on the Multipoint function.

This functionality is available only after updating the Technics Audio Connect application to the latest version. This means that the Airoha hardware is capable of supporting multipoint and LDAC together in a TWS headset. But there is always a catch and the catch is the quality of the LDAC codec. While the English support page does not mention the codec issue, the Japanese one does (Thanks to aborne25 from twitter for highlighting this):

When using multipoint, set the LDAC playback sound quality of the playback device to "best effort".

What does best effort mean? This is LDAC's adaptive bit rate, or variable bit rate for those familiar with MP3. Therefore the bitrate will vary between the 330, 660 or 990 kbps. I was provided this explanation by Aborne25:

A2DP generally works on 1Mbps BR, but LDAC especially 990Kbps works on 2Mbps EDR.  Since Bluetooth cannot handle BR and EDR simultaneously, LDAC 990Kbps and multipoint doesn't work together.

So the highest bitrate available with multipoint is either 660 or 330 kbps. Comparing the the Jabre Elite 75t which only uses AAB or SBC, the highest bitrates would be 320kbps for AAC and up to 345kbps for SBC. If Sony did implement multipoint on the WF-1000XM4, the connection would probably be limited to "best effort" as well. I suspect we might be looking at 330kbps in multipoint, but this will have to be confirmed with testing.

Looking finally to the WF-1000XM4 and multipoint. The Bluetooth hardware would most likely support it as seen with the Technics AZ60, but it would now be up to Sony to release a firmware update to add multipoint. So start asking in Sony's support forums, tag them on Twitter and email Sony about multipoint support.

While I have not heard anything about multipoint being added to the WF-1000XM4, but it would be great for office environments, with both a laptop and phone connected to a WF-1000XM4 or even the new Linkbuds for example.

I am sure more and more Airoha based TWS headsets, even low end devices from Chinese companies will support multipoint in the future. Of course Sony could wait for LE Audio before adding true multipoint to a TWS headset, or even wait for another device like the upcoming YY2950, but with the 1 year release date coming up soon, a nice bonus for users would be the addition of true multipoint support.