The except from the A320 FCOM answers your question:
FWC generates synthetic voice for radio height announcement below 2500 feet. These announcements come through the cockpit loudspeakers even if the speakers are turned off.
Predetermined call out
The altitude call out uses the following predetermined threshold :
height (ft) call out
2500 TWO THOUSAND FIVE HUNDRED OR TWENTY FIVE HUNDRED
2000 TWO THOUSAND
1000 ONE THOUSAND
500 FIVE HUNDRED
400 FOUR HUNDRED
300 THREE HUNDRED
200 TWO HUNDRED
100 ONE HUNDRED
50 FIFTY
40 FORTY
30 THIRTY
20 TWENTY
10 TEN
5 FIVE
DH + 100 HUNDRED ABOVE
DH MINIMUM
Pin programmings allow the operator to select the call outs needed.
If aircraft remains at a height that is in the detection zone for a height callout, the corresponding message is repeated at regular intervals.
Intermediate call out
If time between two consecutive predetermined call outs exceeds a certain threshold, the present height is repeated at regular intervals.
The threshold is : 11 seconds above 50 feet
4 seconds below 50 feet
The repeating interval is 4 seconds.
RETARD announcement
The loudspeaker announces RETARD at 20 feet or at 10 feet if autothrust is active and one autopilot is in LAND mode.
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