How to increase audio volume
Simply turning up a quiet recording clips the loud parts before the quiet parts get loud enough. Here is a better way, and a free tool that does it without uploading the file.
Why a flat volume boost distorts the loud parts
Multiplying every sample in a recording by the same factor, which is what a plain "increase volume" slider does, raises the loudest parts as much as the quietest ones. If the quiet parts need much amplification to become audible, the already-loud parts get pushed past the maximum the format can represent and clip, producing a harsh, crackling distortion.
Normalization vs. a flat boost
Normalizing instead finds the loudest peak in the recording and raises the whole file only as much as that peak allows without clipping, which is safe but limited: a recording with one loud spike and mostly quiet speech still ends up quiet overall, since that one peak sets the ceiling. Dynamic range compression goes further, reducing the gap between loud and quiet parts first so the whole thing can then be pushed louder evenly, which is what most "loudness" tools actually do under the hood.
In a full audio editor
Audacity, free and open-source, has both a Normalize and an Amplify effect and does this properly, but it is a full application to download, install and learn for a job that is often just "make this one voice memo louder."
Boosting volume without uploading the file
Stayput's volume booster raises or lowers the loudness of an MP3, voice memo or video directly in the browser tab, with a normalize option that brings quiet audio up to a target loudness without clipping the peaks, and a batch mode that evens out a folder of recordings to the same level. Nothing is uploaded to process it.
Questions
Why does my quiet recording distort when I turn up the volume?
A flat volume increase raises loud and quiet parts by the same amount, so by the time the quiet parts are audible, the loud parts have been pushed past the format's maximum and clip into distortion.
What is audio normalization?
Raising a whole recording's volume by the largest amount possible without its loudest peak clipping, which is safer than a flat boost but still limited by that one peak.
Can I make several recordings the same volume at once?
Yes, Stayput's volume booster has a batch mode that normalizes a group of files to a matching loudness level in one pass.
Does boosting the volume work on a video's audio too?
Yes, Stayput's volume booster accepts video files and adjusts the audio track without needing to extract it first.