LGT WAS CLEARED TO DESCEND TO 12000' BUT DESCENDED TO 11000'.

Narrative

THE FOLLOWING ATC CLRNC IS WHAT WE PERCEIVED (OR WHAT WE THOUGHT WE COPIED AND THOUGHT WE READ BACK VERIFYING SAME). ONLY THE TAPES CAN PROVE OUR ACTUAL CLRNC AND THE ACTUAL READBACKS. WHILE AT A CRUISING ALT OF FL280 N OF AUSTIN WITH OUR DEST BEING SAN ANTONIO; WE RECEIVED A CLRNC TO; 'DESCENDED TO CROSS A POINT 11 MI N OF AUSTIN AT FL240.' WHILE DSNDING TO COMPLY; WE RECEIVED AN ADDITIONAL CLRNC TO DESCENDED TO CROSS THE SAME POINT AT OR BELOW FL240 AND TO CROSS MARCS AT AND MAINTAIN 11000'. THE CTLR REQUESTED OUR ALT. AFTER STATING 11000'; THE CTLR CAME BACK THAT OUR CLRNC WAS TO CROSS MARCS AT '12000''! AFTER ADDING PWR AND INITIATING A CLB ANOTHER CTLR CLRED US TO REMAIN AT 11000'. AT THIS POINT AND AS STATED BEFORE AND W/O THE TAPES; I CANNOT BE ABSOLUTELY CERTAIN OF WHAT THE ACTUAL CLRNC AND ACTUAL READBACK WERE. THE F/O BELIEVES THE CLRNC TO HAVE BEEN AND READ BACK THE SAME TO 'CROSS MARCS AT 11000'.' THE F/E WAS ATTENDING TO OTHER DUTIES AND WAS NOT MONITORING THE RADIO AT THE POINT. IF THE ACTUAL CLRNC WAS TO CROSS MARCS AT 12000'; I CAN ONLY SPECULATE WHY WE THOUGHT THE CLRNC TO BE 11000'. MAYBE THE POINT 11 MI N OF AUSTIN IN THE CLRNC CONFUSED US. IF THIS CONFUSED US; IT MAY CONFUSE OTHERS. AS A SUGGESTION; MAYBE THE XING POINT N OF AUSTIN SHOULD BE CHANGED TO 12 MI. IF INDEED THE ACTUAL CLRNC WAS TO CROSS MARCS AT 11000'; OR IF THE CLRNC WAS TO CROSS AT 12000' AND WE COPIED AND READ BACK CROSS AT 11000'; THEN I FEEL THE CTLR WAS IN ERROR FOR EITHER GIVING US THE 11000' XING OR FOR NOT CATCHING OUR READBACK VERIFICATION OF THE XING TO BE AT 11000'.