Tone quality seems to be an issue that no singer ever closes the book on. It's an ever-ongoing process to work on your tone and voice colors. 

There are several elements that all influence the quality of your tone, so it's the subtleties that can make a big difference. It will take a lot of practice to notice the minute details in your voice and how they change when you do different things, such as opening your throat or relaxing your jaw and neck. 

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