In Herbst Theater tonight, Thomas Hampson offered the second all-Mahler recital in three days, once again accompanied to perfection by Craig Rutenberg. But Hampson entered the stage alone at the beginning of the concert, and presented a fascinating, if somewhat rambling, 10-minute speech about what he called "the nature of song recitals," leading up to a suggestion that if the audience follows the the text, it may be detrimental to full appreciation of the work. Rather than leaving matters on the level of a hint, Hampson said lights will be dimmed during the first set ("to wean you") and then completely turned off. (At the end of the concert, he asked what the audience thought of the idea, and he got a mixed response.) Hampson said the text and program notes ("you have good ones tonight, I know because I wrote them") should be read before and after the recital, not during. He urged the audience to focus beyond the text, "beyond me and Craig, perhaps even beyond Mahler." All this, coming from a lesser artist would have been irritating at best, a turnoff at worst, but Hampson made his case so convincingly, and he delivered such a powerful performance that the matter became just a slight inconvenience. Just as Friday, there were some problems with intonation (something new from Hampson), but the gestalt of his presentation -- intelligence, flawless diction, sincerity, a great deal of charm -- pushed everything else into the background as the selections from "Das Knaben Wunderhorn" marched by from "Spring Morning" to "Primeval Light." The two-concert series will be repeated in New York next month. Don't miss it, but take a flashlight. Janos Gereben/SF [log in to unmask]