Testing with the fdkaac binary coming with the foobar2000 encoder pack, latest available version.
The sample is in 44100hz / 16 bits per sample, so it's not about dithering and stuff like that.
The problem is that the "pop" at the very beginning sounds very different after encode with mode VBR 4 or 5. Even pushing the bitrate really to the limit (512 kbps CBR) doesn't help here at all.
The amount of silence before the "pop" doesn't seem to matter, I just added 1 second so that it's easier to test (in case someone's device doesn't start producing sound immediately)
Log for VBR 5:
foo_abx 2.0.6c report
File A: 20hz with pause and fadeout 16bit.flac
File B: 20hz with pause and fadeout 16bit fdkaac vbr 5.m4a
WASAPI (shared) : Out: default
22:51:08 : Test started.
22:51:56 : 01/01
22:52:07 : 02/02
22:52:27 : 03/03
22:52:38 : 04/04
22:52:44 : 05/05
22:52:50 : 06/06
22:52:56 : 07/07
22:53:02 : 08/08
22:53:08 : 09/09
22:53:13 : 10/10
22:53:18 : 11/11
22:53:23 : 12/12
22:53:29 : 13/13
22:53:34 : 14/14
22:53:40 : 15/15
22:53:50 : 16/16
22:53:50 : Test finished.
p-value: 0 (0%)
-- signature --
Can also do log for CBR 512 if needed but you can trust me, it's just the same problem, not affected by bitrate.
Version: (written in the file tags but just in case)
$ wine ~/Documents/foobar2000/encoders/fdkaac/fdkaac.exe --help
Usage: fdkaac [options] input_file
VBR 4 or 5
P.S. I'm not saying than 1..3 are unaffected, I just didn't bother to test them. They probably are just the same.
Testing with the fdkaac binary coming with the foobar2000 encoder pack
But there is no FDK encoder in foobar2000 encoder pack.
Wait a sec...
I'll delete it and reinstall and check. I thought it was from there.
Yes, you're right. The dumbass in me thought that it's from the fb2k encoder pack, but actually it's from somewhere else, I have no idea because I forgot. Either I compiled it myself, or ....
So that kind of invalidates the claim, unless someone else wishes to try to encode this sample, because I'd rather give up than go through necessary steps to compile it (IIRC, last time I checked, it wasn't easy)
Or maybe I'll try to build it from source later. And post details on how it was made. (just in case it's a problem with the specific build)