The "In Concert" record is relatively early in her career (1962). What you describe is simply her voice and singing style. For some, the absolutely crystal clarity of her voice is totally enchanting; for others, her voice is sharp and thin and not very pleasant. And, as you describe, her use of vibrato can be off-setting. But so many of us who grew up in the 60s grew up with folk music, protest songs, and Joan Baez. She's an icon of her generation.
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