Sentence:  His life-long friend , Serge Koussevitzky , gave unreservedly of his praise and brilliant performances in Boston , New York , and Washington , D. C. , to which he added broadcastings and <WSD>recordings</WSD> for the whole nation . 
Meaning of the word marked with <WSD> tags:  a signal that encodes something (e.g., picture or sound) that has been recorded