For Windows users. Since utilities to calculate replay gain/peak values are mostly designed for compressed "lossy" formats such as mp3, enabling ReplayGain for wav tracks/albums, is a problem. I found a workaround was encoding mp3s from wav sources and using Winamp (v5.8) to both calculate and write the ReplayGain to the mp3 id3v2.3 tags, then applying those values to the original wavs. There's a Windows freeware tool that copies id3 tags directly onto an existing wav file called Mp3tag. Below is a screenshot:
In your player that supports ReplayGain playback simply enable it. In VLC the option called 'Replay gain mode' allows you to select: 'Album', 'Track' or 'None'.
I hope this answer still has relevance. ReplayGain is especially useful for chamber music in my limited experience.
For that track above I also measured the 'Perceived Loudness' (before ReplayGain) in dB. It was, Left: -11.82; Right: -12.22. The whole track should hence be louder, much louder, when Winamp's ReplayGain value -5.26 dB is applied, however, in practice, track playback becomes somewhat quieter on good headphones.
My understanding is that -5.26 dB track gain is an average figure when applied that falls below the left/right peak amplitudes to avoid clipping artefacts above 0 dB. Average 'Loudness', another value, is subtracted from a -14 dB pink noise reference. ReplayGain attenuates or raises the peak amplitude in line with either the Album or the Track average. I have encountered so far significantly more tracks in which volume decreases as a result of using ReplayGain. The net effect is usually to normalize the loudness and in the process lower the volume.
I may be wrong of course, but whether in dB or LUFS, 'Perceived Loudness' is that which you want to manipulate or change.
People write volumes trying to explain all this.
Edit: It turns out that ReplayGain multiplies each sample value by a constant.
Ten raised to the power of one-twentieth of replay gain. In short, if the ReplayGain is put at -5.26 dB (as computed by Winamp), sample values across the board should be multiplied by 0.54575786109127092251134492267094. May this be accurate. I'm citing from: http://wiki.hydrogenaud.io/index.php?title=ReplayGain_1.0_specification
Conclusion: Having normalized the WAV file above by 54.575786109127092251134492267094 percent and compared it to the MP3 version that contains ReplayGain, I must regrettably report that VLC (3.0.11 Vetinari) on Windows 10 fails to respect the metadata in the MP3 tag, if ReplayGain mode is enabled in the Audio Preferences section. ReplayGain ID3 tags inserted into WAV tracks are ignored as well, unsurprisingly. While Winamp does respect these values in the ID3v2.3 tags in MP3s, as does PowerAmp on Android, Winamp also does not recognize the WAV file tags, to my astonishment. It implements a default gain in the absence of proper ReplayGain.
Back to the question: How to ensure uniform sound levels in multiple WAV files?
My normalized WAV played back in Winamp sounds exactly the same as the MP3 with RG. The formula "ten raised to the power of one-twentieth of replay gain" therefore, in this instance, replicated ReplayGain accurately. You can probably rely on the formula, using Winamp to obtain ReplayGain. A better option might be to normalize loudness in music tracks of varying loudnesses employing one of the other standards. EBU R128 set to -23 LUFS has been recommended, I think.
Edit: Minor correction. VLC applies ReplayGain to MP3s (not to WAV files), provided the RG metadata exists. You must relaunch the player (in Windows) after you enable Replay gain mode under Audio Preferences. Then it works fine. My mistake.