>No offence, but this test was solely based on "user preference".
That's how testing works in the audio industry. Mainly because it's the only thing that makes sense.
>- Wheres the Spectrum analysis of each codec?
A spectrum tells you almost nothing about how a codec sounds. Thus listening tests.
>- Which codec is more true to the original .wav, using the above data as comparison?
That's what a listening test answers. I know very few people who listen to music by unplugging their speakers, watching the spectrogram scroll by, and pretending to know what it sounds like.
>- Which codec cuts below 50hz?
Only telephony codecs do that; the highpass improves speech intelligibility according the studies done by Bell Labs.
Opus has a 3Hz highpass to eliminate spectral leakage in samples with a DC offset.
>- Which codec emphasizes certain frequencies (8-10khz, typical LAME mp3)?
Listening tests will tell you that. A spectrogram will not. Some amount of detailed critical band energy analysis can give you quantization bias figures, but that still won't tell you how it sounds. That's a test you run _after_ hearing a boost to determine where it's coming from.
>- I'll automatically assume
That's why I'm taking offense.
> your Opus codec (which is based on a voice codec) prioritizes bitrate quality between 500hz-4khz.
No. Opus is based on CELT, a music codec, and SILK, a speech codec. You didn't even read the demo page? Dude, tons of pretty pictures. You missed the party hat though.