I've heard that it's good to sing what you play on a piano. Singing chord is not possible but bass lines would be. Bass lines are sometimes played a octave lower than what a male person can sing but I guess you could transpose them octave higher. Does anyone have any proven evidence that singing bass lines help with learn to play them on the piano? and if so did they have to sing them an octave higher due to bass lines being too low in range?
Yes, singing any line before and as you play will help. George Benson is one to listen to for example.The octave doesn't matter a jot. In fact, if you think about it, females will have to sing that bass line an extra octave higher in most cases.
If you get used to trying to sing a line prior to playing it, it'll improve sight reading as well as phrasing and playing generally. When improvising, I get students to sing a phrase in the key they're in, then play it. Sort of 'in their mind's ear'.
If you're starting out learning piano, then playing and singing any line, simultaneously and separately, will implant it into memory far better than just playing it with fingers. Come to think of it, it works for all levels, advanced as well. Not so easy on sax or trumpet,for the former, though...
'Sing it before you play it' is not, on piano at any rate, much about hitting the right note (more so on other instruments perhaps, but on piano you don't have to 'make' the note the way a wind player does), but it can help with playing the right rhythms. It's a lot easier to sing a phrase in time than to play it in time if you're fumbling to put your fingers on the right notes!