Every encoding tool I've seen & use, All use Apple AAC in the QAAC wrapper. At ~160kbps VBR, It far better than Vorbis which needs 256kbps in some genres like Noise/Industrial and MP3 is just severely outdated needing V0 or 320kbps to be transparent. I use FHG AAC(winamp encoder) as a fail safe measure when Apple encoder chokes on something.