Chris:
Are there no "hot" (pilot-headset) microphone channels?
Not according to the Airbus SDN document I have in front of me.
The crew channels that are recorded are effectively the headset signals, hence only include 'PTT'd' signals, not the live (hot) mic signals from each crew member microphone. The inference in the SDN is that audio not 'transmitted' by either radio or intercom, will be picked up by the area mic.
grity:
@GY did you think it can be possible to extrakt a speed info from chanel 4 in case of UAS if you compare the chanel 4 with the sound before an UAS event? (with given altitude...)
Some estimation could be made of speed based on the audio signature, given we have altitude references, and some prior recording segments to act as baselines - you would need this since 250 kts CAS @ FL350, can sound the same as 300 kts CAS @FL200 (numbers made up for demonstrative purposes). However these would likely only be very rough numbers (say in a 30-50 kt range), but if the assumption is that the aircraft lost it's speed data sensors, then this would be one method to provide an estimation of speed.