SoundExpert explained
Reply #71 – 2010-12-02 18:24:44
Now with SBR and PS we have another revolution where the waveform isn't an (inaudibly) distorted version of the original, but actually bares no resemblance to the original. So any measurements that include psychoacoustics while assuming that the waveform should be at least vaguely similar are also broken. Below are Diff. Levels of 9 SE samples processed by HE and LC profiles of CT encoder (@128 kbit/s): aac+ CBR@128.9 (Winamp 5.21) aac CBR@129.6 (Winamp 5.21) ---------------------------------------------------------------------------------- BAH: -34.4139 dB -33.6044 dB BAS: -35.8823 dB -36.6633 dB CST: -9.9989 dB -21.8093 dB FMS: -30.0811 dB -36.1838 dB GLK: -19.6055 dB -36.1699 dB HRP: -14.6460 dB -21.5798 dB LOB: -16.6801 dB -22.8038 dB MOF: -21.3063 dB -31.3638 dB QRT: -33.6662 dB -33.6656 dB The same for encoders @192 kbit/s: aac+ CBR@192.7 (Winamp 5.24) AAC VBR@190.9 (NeroRef 1530) ---------------------------------------------------------------------------------- BAH: -37.1624 dB -33.0144 dB BAS: -39.2936 dB -32.5532 dB CST: -23.2628 dB -28.0893 dB FMS: -39.2991 dB -33.3562 dB GLK: -33.8942 dB -37.5733 dB HRP: -20.2250 dB -26.7197 dB LOB: -29.0020 dB -29.4662 dB MOF: -34.7739 dB -36.6439 dB QRT: -37.0264 dB -32.7181 dB As you see waveforms of both profiles differ from reference waveforms approx. to th? same degree. So it is an illusion that with SBR the waveforms "bares no resemblance to the original". The illusion is inspired by the knowledge of how SBR works. In reality both waveforms are changed to the same level (@192 HE versions even closer to references than LC ones, though the encoders and modes are different). The main question is how they are changed.