How to fix it? If we take the sound out of the nose, the sound becomes muddy. If we put the sound back to the nose, the sound becomes normal, so to have little nasal in the noise is common.
Exercise
s-f-m-r-d ma-ma-ma-ma-maIf the voice project too back, it sounds muddy.
If we have nasal resonance, we can feel a little vibration right up the nose.
What is bad nasal?
It is more to do with the larynx than it does with the nose. If we make the larynx pretty put, the voice sounds natural. If drop the larynx down, the voice sounds muddy. If put the larynx up, we can hear a bad nasal sound.
An interesting fact is that if we make larynx up and cut off the nasal cavity no resonance, but we still hear the bad nasal sound. So we don't need to have nasal sound via nasal resonance.
Therefore, we should try to keep the larynx at the right position (not too high or too low) or keep the upper body natural. Also, we need to make sure to make a little resonance on the nose when we are singing.