Some of my MP3s are too loud, others too soft, I can amplify & de-amp them and I have, but is it possible to have Audacity look at a group of separate files and adjust their volumes so that they’ll be at the same relative level? This is for listening to ambient-style songs in a playlist, not for burning a CD, that had been recorded at different levels apparently because some are barely audible while others come blasting out. Is this what Normalizing is for? I want each song to have uniform volume. Compression? It’s a lot of songs. Can it be done easily?
version 2.1.2 on Win 10
No. Normalizing is to amplify up to a specified peak level. For example, if you normalize a bunch of files to -1dB, then the maximum peak level will be -1 dB in each of the tracks. “Peak level” is not the same as “loudness”. For example, a solo acoustic guitar music may have high peaks (due to the initial “pluck” on the strings) but overall sound fairly quiet, whereas a “thrash metal” song may have a lower peak level but sound very much louder than the solo acoustic guitar.
The best, quickest and easiest way is to use “Replay Gain” or “Sound Check”.
Many media players have a feature called “Replay Gain” (Apply products have a similar feature called “Sound Check”) which is designed specifically for this purpose.
How it works:
First you scan the tracks using the Replay Gain scanner in your media player. This writes metadata to the files saying how “loud” the track is. This is fairly fast - much quicker than using Audacity or any other audio editor.
Then you play the tracks with “Replay Gain” enabled. The player then automatically adjusts the playback volume so that all of the tracks play at about the same loudness.
Replay Gain has two modes when analyzing (scanning) the tracks. “Track mode” (each track is scanned individually) and “Album mode” (the selected tracks are assumed to be one continuous album, and the average loudness for the “album” is measured. You need to use “Track” mode.
Look in the documentation / manual for your media player for details about Replay Gain (or “Sound Check” if using an iplayer, iTunes or other Apple product).
One of the big advantages of this method is that it does not damage, or change in any way, the audio data in your MP3s. All it does is to analyze and add a special metadata “tag”.
Since you have MP3s, [u]MP3Gain[/u] is an alternative to ReplayGain or Sound Check.
The difference is that ReplayGain and Sound Check work at playback-time whereas MP3Gain “permanently”* changes the volume of the MP3 filess so it works with any MP3 player and any MP3-player software. (And, it works without re-encoding the MP3 so it’s fast and there’s no quality-loss.)
Note that since many (or most) commercial music is normalized (maximized) for 0dB peaks, including quiet-sounding songs, so the only way to match volumes is to reduce the volume of the louder files. Some people complain that their music is too-quiet after applying ReplayGain or MP3Gain, but that’s the trade-off.
Compression?
The difference is that compression (or automatic volume control) works moment-to moment and the above methods work on whole songs (or on whole albums if you choose) so the dynamic contrast within the song is maintained. Compression can change (or damage) the character/quality of the song whereas ReplayGain is like setting the volume control to the “correct” level just before the song starts.
*It can be reversed but It might be a good idea to keep an “archive” of your unmolested MP3s.