1980s digital recordings enhanced by 24-bit processing. Karajan filmed performances of his work for both Unitel and his own company, Telemondial. Critical reception The so-called Karajan sound remains something of a litmus test for critics, dividing them into two competing camps. Two reviews from the Penguin Guide to Compact Discs illustrate this point: Of a 1971–72 studio recording of Tristan und Isolde, the Penguin authors wrote, "Karajan's is a sensual performance of Wagner's masterpiece, caressingly beautiful and with superbly refined playing from the Berlin Philharmonic". Of Karajan's recording of Haydn's "Paris" symphonies, the same authors wrote, "big-band Haydn with a vengeance ... It goes without saying that the quality of the orchestral playing is superb. However, these are heavy-handed accounts, closer to Imperial Berlin than to Paris ... the Minuets are very slow indeed ... These performances are too charmless and wanting in grace to be whole-heartedly recommended." The New York Times writer John Rockwell wrote in 1989: "He had a particular gift for Wagner and above all for Bruckner, whose music he conducted with sovereign command and elevated feeling." Legacy Karajan's concerts came to be considered major cultural events. In a 1982 tour of the United States, musical stars from Zubin Mehta and Seiji Ozawa to Frank Sinatra attended his Carnegie Hall concerts. Karajan was less interested in publicity or legacy than in building the cultural institution of music. "When I am on the podium, I forget all about the public," he said. "I am not interested in publicity. I can only hope there is an advantage to my being known in the world, that through the interest people take in me, they will then move on to an interest in music." Much of Karajan's legacy is inextricable from his pioneering attitude toward recording technology. He made over 800 recordings, far surpassing the output of other contemporary conductors. Deutsche Grammophon said his albums sold ''probably hundreds of millions'' of copies. The West German newsweekly Der Spiegel reported that he earned more than $6 million annually from record sales and conducting fees in 1989. Karajan amassed a fortune valued at 250 million euros as of 2008, remaining one of top-selling classical music artists two decades after his death. Notable students Despite Karajan's significant prowess as a conductor, he was more often seen behind the camera than in the teaching studio, preferring to record rehearsals rather than give masterclasses. He maintained