@shekh:
24 bit example. AviSynth script just as dummy video track. Important part is the WAV file to be used as external audio track (Audio - Audio from other file...), in Audio "Full processing mode" and with a Compressor. Archive contains an MKV with Ut Video and PCM audio track, and to compare, another with MP3 audio track compressed via the FFmpeg Lame MP3 encoder. The result with AAC is broken, did not add this.
Audio driver is an "NVIDIA High Definition Audio" device, general Windows 10 64b.