But as she matured, her voice darkened and gained in substance.

Her voice has darkened with the years.

As he'd reached his majority, Kevin's voice had darkened ever so slightly into a deep tenor that still secretly delighted him.

His voice had darkened with the last sentence, but then he gave himself a shake.

His voice darkened as if he were remembering all the people he had shed.

Sometimes his voice darkens and seems to be floating out of him.

Despite her great success as a soprano, she realized that her entire voice was constantly darkening in color.

His voice darkened like the shadows in the trees surrounding them.

Most voices naturally darken and deepen as a singer matures.

His voice darkened, and even his nose grew menacing.