Complex sentence: An expressive singer with a bittersweet, clear tone, she softened her initial hard blues/gospel style but while producing several enduring records, her singing career was probably affected by an overall lack of worthy material.
Split into simpler sentences: An expressive singer with a bittersweet, clear tone, she had softened her initial hard blues/gospel style. Although she produced several enduring records, her singing career was probably affected by an overall lack of worthy material.