Is zeroing appropriate MDCT samples acceptable as a lowpass filter in AAC? What are other recommended/possible ways of implementing the lowpass?

Daniel

You wouldn't want to waste any bits on the zeroed portion of the spectrum, so why not
just limit max_sfb?

Tim.

Too coarse. If 49 bands are cut to 41 (bin 736) cut-off is 15850 Hz. If I cut at band 40 (bin 704) cut-off is 15160 Hz. I have no possibility to cut in-between.

What I do is use both, limit number of bands and than zero some samples at the end of that band. For example to get 15500 cut-off (bin 1 to 719) I have 41 bands but bins 720 to 736 are zeroed (bins 736 to 1024 are not coded anyway).

But I am unsure about how good this MDCT filter is...

It's not as good as a FIR filter in the time-domain, but it's appropriate enough I guess. Try encoding a sine sweep, you'll notice some alias effects.

SebastianG