This is a good method to practice the chords and train the ear!
If you mean to reduce a song written in chords to one single voice ... that's impossible.
But you can try this:
e.g.:We shall over come
singing two 16th (l.h. root and 3rd) and holding the melody note (r.h.) as a quarter note or even a half note.
domiso__ domiso__ domila__ domila__ domiso_ domisofa ....
The example of all examples is the prelude in C by Bach. You can sing the arpeggios like Arvo Paert plays it in a fast tempo. Try this out and then you can do it with a slow song always starting with the triad root or bass note.
You can download any piece or song in double speed and sing the lowest pitch and the highest pitch and imagine the middle parts of the chords. But you can also sing it slow ... as you like.
also this is an interesting exercice:
BWV 114 you can practice as following:
- Play the bass line l.h. and sing the melody Play the melody r.h. and
sing the bass line
Sing the bass line and "listen" to your inner ear the melody and vice
Sing the chord as triad domiso
You can also try to sing both lines skipping from the lower to the upper part, but this has to happen very slowly ...
BWV 114 is not so practicable like other pieces by Bach as e.g. BWV 999
The Largo of Stravinsky's Sonata looks as a good example to try singing both parts as one skipping from the l.h. to the r.h.