1Upload the AAC audio files whose level you want to change.
2Set a gain in decibels or as a percentage — positive to boost, negative to bring it down.
3Run it; headroom is checked first, so a boost that would clip is flagged rather than silently squared off.
4Download the adjusted AAC file.
Adjust AAC Volume FAQ
How does Adjust AAC Volume change the level?
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Concretely, the gain is applied after decoding and the file is re-encoded, which costs one generation — so set the level you want in one pass rather than nudging it repeatedly, and use normalisation instead if what you want is a consistent perceived loudness. You set a gain in decibels or as a percentage and it is applied uniformly across the whole file.
Will boosting the volume distort the audio?
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Only if it clips. Headroom is checked before the file is written, so a boost that would push peaks past full scale is flagged rather than silently squared off. If the recording is quiet because it is noisy, boosting raises the noise too.
Does the source format matter?
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It does. AAC is the MP4-family lossy codec, audibly better than MP3 at the same bitrate and the default for Apple devices. That decides whether a gain change is an exact edit of the samples or has to go through a re-encode.
Anything specific to AAC to know?
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Yes — AAC carries encoder delay in the container, so a naive cut can leave a few milliseconds of silence that a proper trim removes. Relevant if you plan to adjust the level more than once.
Should I use volume or normalisation?
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Use volume when you know exactly how much louder or quieter you want it. Use normalisation when you want a set of files to end up at the same perceived loudness — that is a measurement problem, not a fixed gain, and applying one when you meant the other is the usual mistake.
Can I adjust a whole batch to the same gain?
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Yes, though be careful what you are asking for: the same gain on files recorded at different levels keeps them at different levels. If you want them to match, normalise instead.
What can I upload to Adjust AAC Volume?
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MP3, AAC, M4A, OGG, Opus and WMA are the lossy codecs handled directly, and lossless sources (WAV, FLAC, AIFF) can go in the same batch. The codec is probed from the stream, so an incorrectly named file still works.
Is there a file size limit on Adjust AAC Volume?
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Yes: free accounts process audio up to 200 MB per file, which at typical bitrates is several hours of material; ffmpeg does the decoding and encoding, exactly as it would on a desktop. That is the most generous cap on the site after video, and audio work rarely runs into it.
Will Adjust AAC Volume lower the quality of my AAC audio files?
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A lossy file has already discarded detail once, and re-encoding discards more — that is generation loss and it does not undo. Wherever the job can be completed by copying the encoded stream rather than re-encoding it, that is what happens, and the audio comes back bit-identical.
Can I run Adjust AAC Volume on several AAC audio files at once?
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Yes. Upload the set and they process in parallel with the same settings, which is the practical way to handle a podcast series or an album rather than repeating the job by hand.
Do tags and cover art survive?
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Yes. ID3, Vorbis comments and MP4 metadata atoms are carried across, cover art included, so a processed file still sorts correctly in a music library. ReplayGain values are recalculated rather than copied, because a stale one is worse than none.
Does Adjust AAC Volume cost anything?
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No. Adjust AAC Volume is free without an account and adds no audio watermark or spoken tag to the output. Your upload is deleted from the workers shortly after the job completes.
