According the System Description document issued by Airbus for the Allied Signal CVR, the unit records 4 channels of audio:
Channel 1 - Capt - all audio transmitted by the capt (radio and i/c)
Channel 2 - F/O - all audio transmitted by the F/O (radio and i/c)
Channel 3 - 3rd occupant - all audio transmitted by the 3rd crew (radio and i/c)
Channel 4 - Cockpit ambient mic
Therefore any background noise, warnings and cautions, etc, along with non-transmitted audio (crew chat) would have been picked up on the 4th channel.
Doesn't the FWC issue normal rad alt height call outs during descent? Synthetic voice callouts are issued in increments of 100 feet starting at 300 feet down to 100, and then at 50 feet in 10 foot increments.
- GY