I am a bit bewildered by the absence of any indication of a structural failure or decompression on the CVR over a multi-second period.
Assuming the FDR data trace is accurate (as well as my eyesight), the first parameter for which data is lost is engine pressure ratio for the #1 engine at 07:27:55. Most other parameters are lost around 07:27:57, with pitch being the last parameter with data recorded, stopping at 07:27:58.
The CVR stops at 07:28:03. Thus, there appears to be an interval of 7 to 8 seconds between initial loss of an FDR parameter and loss of CVR data. This would seem to be adequate time for some indication of a significant decompression to have been recorded on the CVR.
As I understand it, the data cables to the CVR and FDR run along the upper left of the cabin, and the power supply for these runs along the upper right. In a progressive failure, one might still briefly have power to the CVR and FDR and no data, or vice versa.
According to AWST, the Chinese radar recorded beacon returns for 9 seconds after the CVR stopped. If these were from transponder 2, on the secondary radio bus, might this indicate the possibility that the crew had radio power for up to 15 seconds after the FDR ceased to operate?
I have seen no mention of comparing CVR sounds to those on the CVR for JAL. I assume that flight was airborne after the aft bulkhead failure for a sufficiently long time that the tape covering event onset was recorded over.