A man can sound loving only if he feels loving, and is loving. The same is vice-versa.
The tone of voice is more important than the content of speech. The content of speech comes from the mind. The tone of voice comes from the heart. The heart always beats the mind.
We can't improve our tone of voice through singing, or riyaaz. It's a total misconception. The tone of voice is directly linked to your heart. If you wish to sound lovely, then work towards making your heart lovely. In sometime you will automatically start sounding lovely.
Tone of voice comes from the tone of heart.