Convert Sheet Music to Audio Files

Lifeforms

There are a few programs out there, but it's time consuming, and expensive. There is one called PhotoScore which reads scanned music and transforms them into online notation (can thus be played as various formats, for example can be exported as mp3).
I use this one in conjunction with Sibelius for a full music/notation package. Priced alone at £199 it's not a one off use Thing is it is not so easy to do, there is no perfect package that will do it, and will at the end produce a perfect result. Sometimes depending on the score itself the results can be dire to awesome, with little editing to full editing (as if you were inputting the score by hand from scratch) Mileage varies and no "free" version I found before would do anything near the results I can potentially get from PhotoScore. Not really an option for you due to price.

How quick do you need the music done? In the mean time ask on your local freegle/freecycle for someone who can read music to play the tune (or even a singer to sing it) and if they can record it for you.

If it's going to be a future thing that you do, you might want to start to teach yourself music, it's not instantly easy, but it's also not insanely hard.

The only way I can explain how the likes of PhotoScore works is you take a sheet of music, scan it in, and it reads it. Just like any normal text OCR works. You then potentially have a lot of editing because like the normal text OCR it is never perfect. This involves a lot back and forward checking and editing before anything is correct, which is easy if you know music and thus can recognise note value/position just time consuming.

Sometimes the score it scans and reads is a good score and it's minimal, but introduce hand written scores and it's sometimes just easier to skip scanning it, and manually enter it in sibelius (or other chosen notation package). If you play it as it scans it wont be right, because often the missing parts are things like bar ends, time sigs, tempo instructions, and notes itself. It's the best, but by far the results aren't the best. Time improves it.

It would usually be Scan normally -> edit in graphics package, greyscale/black and white/check resolution -> save as suitable format -> open in PhotoScore -> have it read -> spend a while changing mistakes, making it look exactly on original score -> save -> send to Sibelius and possibly touch up mistakes in there, then -> export as mp3. Mind you, you can play it in photoscore as a midi so could record it straight from there.

Caitlin_Bree

I know you said you'd checked youtube and found many "glorias" but did you find any "the glorias"?
There's one on there from the 4th century AD on The Church Authentic's channel.
The start of the lyrics are "glory to God in the highest and peace to his people on earth, Lord God heavenly king, almighty father, we worship you".

I'm assuming it isn't the right one but thought I'd post in case you missed it.
(oh well, worth a shot)

Jivesinger

There are many, many settings of the Mass which contain a Gloria. And the words are pretty much always the same although often they're in Latin. (Accordingly, the "Lamb of God" is often known as the "Agnus Dei" as the Latin name.)

This is one case when a lyric search may not be very helpful at narrowing it down. .

I've a feeling that Blessed Dominic lived quite some time after the 4th Century AD.