His voice deepened, evidence of the way the memory affected him.

As he spoke, his voice deepened and emptied, grew older.

Her voice deepened in intensity for a moment, then became reflective.

His voice had deepened with anger and, I think, fear.

Then, suddenly, her voice deepened and began to toll like a mighty bell.

Her voice deepened, because only her heart knew what she needed.

His voice had not yet fully deepened, but it was well modulated.

No, for his voice would never have deepened so.

His voice deepened a little, louder and clearer than it had been.

The man's voice had deepened slightly and the usual manner was missing.