The thing is, people shouldn't have to come round and knock on your door, whilst in their PJs at 1 in the morning,not make you aware that they aren't enjoying your noise. It's not their responsibility to do this - it's yours to be simply aware of the impact of your actions on others.....land not do things which impact negatively.
They aren't really being passive aggressive are they? They are trying to avoid conflict....because if they speak to you about this, they fear being rude or damaging the relationship...and because they rightly feel, why should they have to discuss it with you....again, it's so blindingly obvious that they shouldn't have to raise it with you.
What will improve relations? As others say, apologising again, perhaps giving a bottle of wine or flowers, PLUS making clear that you won't be spontaneously having parties again or running into the small hours. I don't think you need to say you will never do karaoke again - you can do that if you want...BUT in a considerate way - that means warning them in advance and making sure it finishes well before midnight and certainly not doing it on a weeknight.
People are entitled to have the odd party. Parties are by nature noisy, but it's all about how you approach them and communication. Always tell people in advance, always keep noise to a minimum, always finish at a decent hour, only do it very occasionally, and probably offer a small gift afterwards,such as wine or chocolates. Acknowledging to yourself and the neighbours that what you have planned and are doing is a bit of a nuisance is really important.