ACR MLG ALT DEVIATION EXCURSION FROM CLRNC ALT DUE CLRNC INTERP.

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I WAS CAPT ON FLT FROM STL TO DFW. WE WERE EXECUTING THE BLUE RIDGE 2 STAR ARR TO DFW. THE F/O WAS FLYING THAT LEG IN INSTRUMENT CONDITIONS. THE ACFT WAS A 2-M; 2 ENG TURBO JET. DSNDING THROUGH APPROX 26000' I TOLD THE F/O I WAS OFF ATC TO TALK TO MAINT. WE WERE APPROX 110 NM OUT. THIS IS A NORMAL COMPANY PROC WHERE WE ALERT OUR COMPANY MAINT OF DISCREPANCIES THE ACFT HAS ON ARR. WHILE I WAS OFF ATC; THE F/O RECEIVED A DES CLRNC WHICH HE READ BACK TWICE. WHEN I HEARD HIM REPEATING THE CLRNC; I RETURNED TO MONITOR ATC AND SAID; 'I'M BACK.' HE SAID WE WERE CLRD TO 11000'; CROSS 5 S OF BLUE RIDGE AT 13000' OR BELOW; AND MAINTAIN 11000'; CROSS ALKID AT 11000'. HE SET AND ARMED 11000' IN THE FLT DIRECTOR'S ALT WINDOW. I DID NOT HEAR THE CTLR'S INSTRUCTIONS OR THE F/O'S READBACK (TO UNDERSTAND IT). WE WERE 6 DME N OF BLUE RIDGE VOR WHEN GOING THROUGH 13000'. I FOR SOME REASON CALLED CENTER AND RPTED LEAVING 13000' FOR 11000'. THE CTLR IMMEDIATELY CAME BACK AND SAID; 'NEGATIVE; RETURN TO 13000' IMMEDIATELY; TFC IS AHEAD AT 12000'; 4 MI.' I TOOK THE ACFT OFF AUTOPLT AND IMMEDIATELY PULLED UP TO 13000'. I SAW MY ALTIMETER BOTTOM OUT AT 12400'. JUST AS WE ARRIVED BACK AT 13000' THE CTLR SAID; 'THE ACFT IS AHEAD (AT 12000') 2 NM'S.' I MISSPOKE AND SAID WE'RE AT 12000'; WHEN I MEANT 13000' WHICH I CORRECTED. I TOLD THE CTLR THAT WE HAD UNDERSTOOD THE CLRNC AS STATED ABOVE AND HE SAID WE WERE CLRD TO CROSS 5 S OF BLUE RIDGE AT 13000'; THEN DES TO CROSS ALKID AT 11000'. I ACKNOWLEDGED AND WE CONTINUED THE APCH UNEVENTFULLY. THE F/O READ BACK THE INITIAL CLRNC TWICE; THEN RELAYED IT TO ME. IF HE READ IT BACK CORRECTLY TO ATC; HE STILL MISUNDERSTOOD BECAUSE HIS VERSION IS DIFFERENT THAN THE ATC CTLR'S VERSION. THERE ARE SEVERAL POSSIBLE CONTRIBUTING FACTORS. THE F/O IS NEW (APPROX 50 FLT HRS) TO THE MLG. ALTHOUGH HE IS AN EXPERIENCED F/O IN THE LGT; THESE ACFT HAVE RADICALLY DIFFERENT FLT DIRECTORS. PERHAPS I SHOULD HAVE STAYED WITH HIM MORE CLOSELY; HOWEVER THIS WAS OUR SIXTH LEG IN 2 DAYS; AND HE WAS HAVING NO DIFFICULTY UP TO THEN. MY CALLING COMPANY MAINT IS A STANDARD PROC WHICH LEAVES ONE PLT MONITORING ATC WHEN ABOUT 100 MI OR SO OUT; AND IS A POTENTIAL CONTRIBUTING FACTOR TO SUCH ERRORS. I INTEND TO MAKE MY OPINION OF THIS AND THIS INCIDENT KNOWN TO MY COMPANY. THE FLT DIRECTOR HAS THE ABILITY TO SET (ARM) ONE ALT AT A TIME. WHILE THE CLRNC WAS NOT UNUSUAL IF GIVEN IN EITHER VERSION; I BELIEVE IT IS BETTER NOT TO ISSUE MULTIPLE ALT CLRNCS IF POSSIBLE BECAUSE OF THE POTENTIAL FOR ERROR. I DON'T MEAN TO EXCUSE THE PRACTICE OF NOT WRITING CLRNCS DOWN; IT'S NOT USUALLY DONE BECAUSE OF THE ARMING ALT FEATURE; AND WOULD NOT HAVE HELPED HERE AS THE CLRNC WAS NEVER PROPERLY UNDERSTOOD.