Music quality is associated with file size. True?

People often say that "if the audio size is big, that means the quality is nice". Actually, not really. Let me tell you one true story.

One day when I was surfing with my Facebook, there's Romeo and Cinderella movie video which was performed by Poppin'Party. It was part of BanG Dream x VOCALOID collaboration, so yeah it's normal, except the movie video uses the full version of the song. With my element inspection & dev console magic, I managed to get the audio file (it's not really legal, forgive me). The audio is encoded using AAC-HE encoding, with 48Kbps bitrate and frequency at 44100/22050Hz. The resulting file size is ~1.6MB. If you think the quality is bad, keep reading the story below.

A few days later, one of my friend managed to get 320Kbps MP3 version of the song, and posted a screenshot about it. The screenshot display full artist name, title, and even cover art. However, as you may know, those can be easily edited with many free software (FFmpeg allows you to add artist name and title, and the cover art can be easily obtained from clickable "Poppin'Party" above). When I see his post, I was skeptical about it. so I managed to ask if he can send me the audio file for analysis purpose, in exchange with the AAC-HE version that I have. He lend me the MP3 version, which has size around ~10MB (which is normal for 320Kbps MP3), and I also lend him my AAC-HE version, which is ~1.6MB (almost 10x smaller). He can't tell the difference between his MP3 version and my AAC-HE version sadly, but he only says that mine has lower audio volume (which is not really related).

Now, it's time to put it to FL Studio's "Wave Candy" plugin. First, I set up FL Studio to listen to Stereo Mix (it's rare to find laptop/PC with this feature). First test is to use my AAC-HE version that I got from Facebook. The result? bit surprising. I already knew that AAC-HE has better quality for lower bitrate as low as 32Kbps. The AAC-HE version has ~16KHz fieldity (better band preservation). Then when I test the MP3 file, my guess is correct, the band preservation is only ~12KHZ, way lower than AAC-HE version that I got. I also can differentiate the audio quality with my ear alone, and my ear tells me that the MP3 audio quality is lower than the AAC-HE version.

From that, we can conclude that smaller audio file size doesn't mean lower quality. It depends on encoding used and how lossy it was before re-encoded. Because, as you may know, re-encoding lossy audio degrades the quality even and even more. You also can't trust the file size alone because, say I re-encode that Romeo and Cinderella song (AAC-HE version) to WAV 44100Hz (which yields to ~40MB), I won't gain anything, and in fact I only waste drive space (it will only have ~16KHz fieldity). The quality is then exactly same as AAC-HE version, and if I re-encode the WAV to AAC-HE again, the quality won't be same as the first one.

Then, back to the title of this post. Music quality is associated with file size. True? The answer is FALSE.