For encoding new AAC files, you can adjust the global gain factor:
"I want play ball," the device announced to the kitchen. Leo smiled. That moment at the park—the moment Sam had turned around, surprised and then grinning, and tossed the ball his way—that was his "gain." He finished his draft with the resolution . He found the word and tapped it three times. "I am happy. Happy. Happy."
For creators: Do not apply traditional AAC gain to Atmos files. You will break the panning and distance cues. Leave gain to the spatial renderer. aac gain
But there is another, quieter culprit. A digital phantom lurking in your file metadata. It’s called (or its cousins, ReplayGain and MP3gain). And it is the most important audio feature you’ve probably never heard of.
Inside the AAC bitstream, the decoder reconstructs the audio block by block. The global gain (encoded as scale_factor within the Raw Data Block) is a value that effectively adjusts the amplitude of the entire spectral band before quantization. For encoding new AAC files, you can adjust
fdkaac --bitrate 256k --scale 3 input.wav
YouTube uses AAC-LC at 126-160 kbps. Their system normalizes all content to -14 LUFS. If your uploaded AAC file has metadata gain of +5 dB, YouTube will ignore it and analyze the raw PCM. However, if your file was encoded with excessive global gain (clipping internally), YouTube will preserve that distortion. He found the word and tapped it three times
device resting in front of him. For Leo, words weren't something he spoke with his voice; they were gems he carefully selected from a digital grid.
Try this at home: Queue up "Bitter Sweet Symphony" by The Verve (a famously quiet, dynamic master) followed by "Blinding Lights" by The Weeknd (a brick-walled wall of sound). Without AAC gain, the transition is a jumpscare.