MISINTERP OF CLRNC TO REDUCE SPEED 260 KTS AS DESCEND TO FL260.

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ACFT HAD JUST LEVELED AT FL310 (ABOUT 1 MIN) CENTER CALLED AND GAVE '260.' F/O REACHED AND RESET CABIN PRESSURE AND I STARTED DSCNT TO FL260. AT 30200' CENTER CALLED AND SAID CLB TO FL310 (OR SOME XMISSION OF THIS SORT). I ASKED F/O IF THEY HAD NOT GIVEN US FL260; AND HE SAID; 'NO;' THE '260' WAS 'SLOW TO 260 KTS.' CONTRIBUTING TO THE MISUNDERSTANDING WAS F/O RESETTING CABIN AND THE LOW VOL ON RADIO--LOW TO THE POINT THAT I SHOULD HAVE TURNED VOL UP. WE WENT BACK IMMEDIATELY TO FL310. BALANCE OF FLT WAS UNEVENTFUL. THE CTLR MADE NO COMMENT EXCEPT THE CLB TO FL310. I BELIEVE THE FOLLOWING WERE CONTRIBUTING FACTORS: IN FREQ OF FLYING; I GET OUT OF RHYTHM OF THINGS. WE HAD JUST DISCUSSED DSNDING AT PLT'S DISCRETION; RE: WHEN THE CENTER GIVES YOU AN ALT CHANGE AND DOESN'T SAY 'PD;' YOU START DOWN. THE RESETTING OF CABIN WHICH IS DONE PRIOR TO DSCNT; THE LOW RADIO VOL; THE SMOOTH START OF DSCNT--THE F/O WAS NOT AWARE OF ME STARTING DOWN. WE WERE PAYING ATTN BUT WERE TALKING OF COMPANY MATTERS.