[FFmpeg-user] FFmpeg AAC encoder produces harsh noise on specific voice

[Agent 45]

Hello, FFmpeg team,

I'm encountering a consistent issue when encoding voice with FFmpeg AAC
encoder.
At low and medium bitrates the encoded output contains noticeable and
sometimes harsh noise when encoding specific vocals.
These noise gradually reduce as the bitrate increases.

I’ve attached all files (input and encoded outputs).
Here are the commands used, ffmpeg version 7.1.1:

ffmpeg -i input1.wav -c:a aac -b:a 128k output1_128k.m4a
ffmpeg -i input2.wav -c:a aac -b:a 128k output2_128k.m4a
ffmpeg -i input3.wav -c:a aac -b:a 128k output3_128k.m4a

ffmpeg -i input1.wav -c:a aac -b:a 192k output1_192k.m4a
ffmpeg -i input2.wav -c:a aac -b:a 192k output2_192k.m4a
ffmpeg -i input3.wav -c:a aac -b:a 192k output3_192k.m4a

ffmpeg -i input1.wav -c:a aac -b:a 256k output1_256k.m4a
ffmpeg -i input2.wav -c:a aac -b:a 256k output2_256k.m4a
ffmpeg -i input3.wav -c:a aac -b:a 256k output3_256k.m4a

# Observations:

- All 128k versions contain harsh noise, and almost the same if increase
the bitrate to 160k

- `output1_192k.m4a`: noise at around 0.27s
- `output2_192k.m4a`: No obvious noise detected
- `output3_192k.m4a`: Mild noise at around 0.05s and some noise still
present from 0.3s

- `output1_256k.m4a`: noise at around 0.27s
- `output2_256k.m4a`: No obvious noise detected
- `output3_256k.m4a`: Mild noise around at around 0.05s

- No noise detected when increased to 320k
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