Identify the actual defect
Metallic is a listening description, not one frequency. Compare sustained vowels, consonants and quiet tails. Decide whether the problem is narrow ringing, broad harshness, thin body, unstable texture or excessive sibilance.
Fix locally before globally
Use narrow dynamic resonance control for ringing and de-essing for consonants. Restore body only where it is missing. Broad darkening can hide air and clarity while leaving the original artifact intact.
Protect the performance
Work at matched listening level. Stop when diction dulls, breaths disappear or the lead loses its relationship with the track. A technically smoother vocal is not better if it becomes emotionally smaller.
Know when to regenerate
Severe warbling, broken pitch transitions and shifting vocal identity may not survive processing. Preserve the lyric and musical brief, strengthen vocal behavior direction and generate a cleaner candidate.