Massive low quality AAC Export

Hello,i have a problem with export in Audacity.
First,i am using Windows 8.1 64 bit.

Second,I tried to export to AAC with 500 quality (the highest) yet there was a huge loss in quality.
The thing had Time synchronization Problems,too.
Here’s a pic:
First file kept intact after export.
Both files completely intact before screencap.

Both in 32-bit float 48000hz.

Anyone Knows how to resolve this?

From my reading of that, the show sounds muffled like you’re talking through a towel?


Why has the original track got such a sharp cut-off around 16 kHz? Had it already been compressed in a lossy format?

According to the release notes:

M4A (AAC) exports: The Quality Slider in “Specify AAC Options” has no effect if the FFmpeg library is built with the libvo-aac encoder, as are recommended builds of FFmpeg for Windows and Mac OS X. Workaround: Given the alternative AAC encoders for FFmpeg have other problems as described in these notes, you can instead export as WAV and convert to AAC in iTunes on Windows and Mac.

so it looks like AAC exports are stuck at about 128 kbps. If the original audio had previously been encoded in a lossy format, that will make things worse.