It's tricky to get a vocal recording right on the first try, whether it's your own recording or someone else's. If a vocal track sounds tinny on playback, you may be able to fix it -- or at the very least, make it sound fuller -- by using the free Audacity audio editor.
Open your vocal track in Audacity. Save a copy of the track as an original.
Click the "Effects" menu button and select "Equalizer." Select the lower and middle frequencies and adjust them to be slightly higher than the treble, or high frequencies. Tinniness is caused by a loss of lower and middle frequencies, emphasising the higher frequencies and making the track sound thin. Listen to the track's playback and adjust the frequencies to your taste. If adjusting those frequencies does not adequately improve your track's quality, continue to Step 3.
Create a duplicate track within the normal interface. Duplicating the track and playing both tracks back simultaneously increases the overall volume of the playback, and can allow for finer volume adjustments. If this does not adequately improve the quality of the track, continue to Step 4.
Select a portion of your track that contains silence. Select the "Noise Removal" option from the "Effects" menu and allow the program to remove any ambient sound from the track. Repeat this step for any duplicate tracks you have created. Isolating the voice from any occurring noise may improve its fidelity. If this does not adequately improve the quality of your track, continue to Step 5.
Create another duplicate track. Use the "Stereo Pan" option to pan one of your tracks all the way to the left. Repeat this action on another track and pan it all the way to the right. Leave any other tracks centred in the stereo mix. Adjust the levels of playback for individual tracks to your taste. If this does not adequately improve the quality of the track, it may be necessary to record the source.
Always create a duplicate of your original recording before you begin making adjustments to your track, as you may change a track so much that it will be impossible to return it to its original state.