The Two Hours That Made It Worse
You filmed in an empty room, and discovered in the edit that the audio had a clear echo.
So you opened the noise reduction tool and pushed it to fifty percent. It improved slightly.
So you pushed it further. The echo diminished, and your voice started changing.
So you added another filter to correct what had broken. Then a third. Then raised the high frequencies because the voice had gone muffled. Then lowered them because it had gone shrill.
Two hours later, you listened to the final result.
A metallic voice, as though you were speaking from underwater, with the echo still audible underneath everything.
And those two hours would have been enough to refilm the whole segment in a room with a rug in it.
The Rule Before Anything Else
A bad picture can be improved a lot in the edit. Bad audio has very narrow limits on what can be repaired.
Which is why the best investment in your sound isn't software or a plugin, it's two minutes before filming: close the window, switch off the fan, get closer to the mic, and record ten seconds and listen to them on headphones before you start.
What Editing Can Fix
Level. Raising quiet audio or lowering loud audio, and evening out levels between clips recorded at different times.
Constant noise. A steady hum from an air conditioner or a machine, because its pitch is steady so it can be identified and reduced.
Isolated sounds. A click, a knock, or a cough at one specific moment, which can be removed or lowered.
And very low or very high tones. Frequencies far outside the range of a human voice can be cut with no effect on speech.
And What It Can't Fix
Echo. When your voice bounces off the walls of an empty room, the reflection becomes part of the recording itself. No tool returns it to the wall, and that's where two hours vanished in our story.
Wind. Air striking the mic directly produces a sound that covers speech completely. Prevention is a windshield. There is no cure.
Distortion from excessive level. When audio is recorded louder than the device can handle, the detail is lost permanently. What's lost isn't recoverable.
And speech that wasn't intelligible in the first place. If you couldn't understand it by ear in the raw recording, nobody will understand it after any processing.
And the general rule: editing adjusts what exists. It doesn't create what wasn't recorded.
The Order to Work In
Follow this order, because changing a step invalidates the ones before it.
First: delete what you don't want, the failed sections and isolated noises.
Then reduce constant noise if there is any, using as little as you can get away with. Overdoing it makes the voice metallic and underwater.
Then even out the level between clips, so the viewer doesn't have to adjust their device's volume mid-video.
Then set the music under the speech.
Then listen to the whole video on headphones before publishing.
Levels in Practice
Without complicated technical figures, these rules are enough for a beginner.
Speech is always the loudest, and it's the reference point for everything else.
Music clearly below the speech. If you notice it while someone's talking, it's too loud.
Ambient sound below both, and its presence matters. Complete silence behind speech sounds dead and unnatural.
And don't let the meter touch the far right. Approaching the ceiling means distortion, so always leave headroom.
Common Mistakes
Raising the level too far. It raises the noise with it, so you get loud speech and a loud hiss.
Overdoing noise reduction. The most common mistake of all, leaving the voice sounding like an old phone. The rule: reduce until the noise eases, not until it disappears.
Reviewing on laptop speakers. Computer and laptop speakers hide a lot of flaws. Use headphones.
And forgetting ambient sound. If you remove every gap and butt the speech together, the video sounds artificial. Leave room tone under the speech to bind the clips.
What to Do on Location to Save Yourself Hours
These things leave the audio stage of your edit almost empty.
Record one minute of room tone with no speech, to fill gaps with.
Get closer to the mic, because distance matters more than its price.
Film in a room with furniture and rugs rather than an empty one.
Watch the recording level while filming, not afterwards.
And listen to ten test seconds on headphones before you begin.
And how to choose the right mic is covered in: the best microphones for filming on a phone.
In Short
Fix what can be fixed in the edit, and know that what was ruined in the recording is ruined.
The time you spend trying to rescue bad audio would have been enough to refilm the segment with good audio. And that's usually the right decision.
And the order of all the editing stages is covered in: editing basics: start by deleting, not adding.