How to correctly pronounce Finnish sounds "a" and "ä"
My native language, Portuguese, has an "a" sound that is sort of between the Finnish "ä" and "a".
I looked at an IPA chart for vowel sounds in the two languages and did a comparison.
So, for me it's very difficult to know how to pronounce this sounds correctly. To add to the confusion, when listening to Finnish speakers, sometimes the "ä" sound is pronounced like an front, open-mid "e" sound, and sometimes like the Portuguese "a", which is front,open.
Is it because my ears are unaccustomed with those sounds or because they vary (e.g. have alophones) depending who is speaking, the location of the word in the phrase, the presence of certain letters, etc?
For example, I find very difficult to pronounce Tämä, because any vowel located before "m" or "n" in Portuguese is nasalized and I need to pronounce them without nasalizing and at the same time trying to emulate what would be the correct "ä" sound.
Do you have any tips to help me?