MP3Gain — The complete guide to consistent volume.

Version 7.0.0 for macOS · Version 2.0.0 for iPhone & iPad — professional loudness normalization, from your first file to your entire library.

Two platforms, one guide: the Mac app leans on drag & drop, output folders, and multi-core batches; the iPhone and iPad app keeps everything one-tap and exports through the share sheet. Where the steps differ, they're labelled macOS and iPhone & iPad.

1. What Does MP3Gain Do?

Have you ever made a playlist where some songs are too quiet and others blast your ears? MP3Gain fixes that.

It analyzes each audio file, measures its loudness, and adjusts it to a consistent level. After processing, all your tracks play at roughly the same volume — no more reaching for the volume knob between songs.

MP3Gain works with MP3, FLAC, M4A, WAV, AIFF, and OGG — on macOS, iPhone, and iPad.

Example: A classical recording at -30 dB and a pop song at -12 dB can both be normalized to the same target level, so they sound equally loud.

2. Quick Start

macOS

Press ⌘ O (or click Add Files) to choose your audio, drag files straight onto the window, or drop a folder to add every track inside it.
Pick a preset — or click the gear icon to set your own target — and check the input → output values shown on each row.
Choose where the results should go: an output folder (remembered between launches) or Replace original file.
Click Start. Watch progress per file, then open the results in Finder with one click.

iPhone & iPad

Tap Select Files to pick audio from the Files app, or From Music Library to import songs you already own.
Tap a file to open its detail view, then choose a preset or build a custom setting.
Tap Start in the bottom bar. Tap Cancel at any time to stop the batch.
Play the original or the processed version to compare, then share the finished files to any app.

That's it! The free plan lets you process up to 3 files per day on every platform; MP3Gain Pro removes the limit.

3. Adding Your Music

macOS

Add Files — the toolbar button, or ⌘ O. Pick one or more audio files.
From Music — imports tracks from your Music library (see troubleshooting if the library won't load).
Drag & drop — drop audio files anywhere on the window, or drop a folder to add every audio file inside it, subfolders included.

iPhone & iPad

Select Files — opens the Files app so you can pick audio from iCloud Drive, On My iPhone, or another provider.
From Music Library — imports songs you own; DRM-protected items can't be processed.
Open in MP3Gain — in another app, share an audio file and choose MP3Gain to send it straight into the queue.

Once added, each file shows its name, duration and format details, the measured input level, and the target you've set. On the Mac these appear as rows in the main window; on iPhone and iPad they're cards you can tap for details.

Tip: The right arrow (→) between input and output info shows the direction of processing — from original to processed.

4. Choosing a Method

MP3Gain offers three ways to adjust volume. The right choice depends on your goal:

EBU R128 — Loudness (Recommended)

Uses the EBU R128 broadcast standard. This method measures how loud a track sounds to human ears, not just the electrical signal. It's the best choice for playlists and albums because tracks will feel equally loud even if they're very different types of music.

Best for: playlists, albums, podcasts, video soundtracks.

RMS — Volume

Adjusts the average signal level (RMS) to a specific decibel value. A straightforward approach — you set a target number and MP3Gain moves everything to that level. Less sophisticated than EBU R128, but faster and simpler.

Best for: quick adjustments when you know your target dB level.

Peak — Limit

Prevents clipping — the harsh distortion that happens when a signal exceeds the maximum digital level. This mode ensures no part of the audio goes above your set limit. It doesn't make quiet parts louder, it only caps the loudest peaks.

Best for: fixing recordings that distort, or setting a safety ceiling before uploading to streaming platforms.

5. Fine-Tuning Settings

On the Mac, click the gear icon on a row to open the inspector. On iPhone and iPad, tap a file to open its detail view — you can then Apply the setting to that file or Apply to all of them.

Using EBU R128 Mode

Three sliders let you fine-tune the result:

Integrated Loudness — The overall loudness target. Lower numbers (more negative) = quieter. Higher (closer to 0) = louder. Streaming platforms typically use around -14 to -24 LUFS.
Loudness Range — How much the volume can vary within a track. Lower = more consistent. Higher = more dynamic range preserved.
True Peak — The absolute maximum level. Setting this to -1 or -2 dB leaves a small safety margin to prevent distortion on playback devices.

Using RMS or Peak Mode

A single slider controls the target level in decibels (dB). RMS mode sets the average level; Peak mode sets the maximum.

You can type exact numbers into the value fields next to each slider for precision.

What are LUFS? LUFS stands for "Loudness Units relative to Full Scale." It's the standard way to measure how loud audio sounds to human ears. You don't need to understand the science — just know that two files at the same LUFS value will sound equally loud.

6. Processing & Output

Processing Your Files

macOS: the toolbar button switches between Start and Stop depending on the current state. Batches run in parallel — MP3Gain uses half of your Mac's cores, capped at four files at a time.

iPhone & iPad: the bottom bar shows Start once your files are analyzed and turns into Cancel while a batch runs. Files are processed one at a time so the app stays responsive.

Understanding File Status

Each file shows its current state with an icon or progress ring:

Ready	Analyzed and waiting to be processed.
Queued	Waiting for a free slot — on the Mac the number of files processed at once scales with your CPU, up to 4.
Processing	The progress ring fills in as the file is normalized.
Success	Finished. On the Mac, click to reveal the file in Finder; on iPhone and iPad, share it with the share button.
Failed	Something went wrong — the rest of the batch keeps going. Open the log for the exact reason.

Where Do the Files Go?

macOS gives you two choices:

Output folder — click Choose folder (later, Change) to pick where processed files are written. The folder is remembered between launches, and one click reveals it in Finder.
Replace original file — the processed version overwrites each source file in place. The folder selector is disabled while this is on, since no extra folder is needed.

Important: Once you replace the original file, you cannot undo the change. If you want to keep the original, uncheck this option and save to a separate folder.

iPhone & iPad: your originals are never modified. Finished files stay with the app until you share them to Files, Music, AirDrop, or another app.

7. Saving & Reusing Settings

Every platform ships with the same five built-in presets, plus any custom presets you save:

Preset	Method	Target
Default	EBU R128	−23 LUFS · true peak −2 dBTP · range 7 LU
Music	RMS	−20 dB
Podcast	EBU R128	−16 LUFS · true peak −2 dBTP · range 7 LU
Voice	EBU R128	−18 LUFS · true peak −3 dBTP · range 4 LU
Streaming Video	EBU R128	−14 LUFS · true peak −2 dBTP · range 7 LU

Selecting a preset applies its values instantly. To build your own, adjust the settings, save them with a name, and the preset joins your list — custom presets can be deleted, while the built-in five can't. Presets are stored on your own device.

8. Using MP3Gain on iPhone & iPad

The iOS app is built for quick jobs away from the Mac:

Import — Select Files (Files app) or From Music Library, or open an audio file in MP3Gain from another app.
Adjust per file — tap a card to open its detail view, then pick a preset or build a custom setting. Apply sets it for that file; Apply to all pushes it to the whole queue.
Compare — play the original or the processed version right from the card before you decide.
Process — press Start in the bottom bar; Cancel stops the batch cleanly at any point.
Export — share finished files to Files, Music, AirDrop, or any other app with the share sheet.
Log — expand Log for a timestamped record of the run, and share it if you need support.

The free plan gives you 3 files per day; MP3Gain Pro removes the limit for $9.99/year or $19.99 once (lifetime).

9. Keyboard Shortcuts (macOS)

`⌘ O`	Add files (open the file dialog)
`⌘ L`	Show the processing log
`⌫ Delete`	Remove selected files from the list
`Esc`	Close the inspector and other dialogs
`↩ Return`	Confirm settings in a panel

The File menu also offers From Library… and Clear Completed, and the Help menu links to this guide, the home page, and your subscription.

10. Help & Troubleshooting

Processing fails: open the log (⌘L on the Mac, expand Log on iPhone and iPad) and read the entry for that file. Common causes:

The file is corrupted, DRM-protected, or in a format MP3Gain can't read.
The output folder is no longer reachable — an external drive was disconnected, or a saved folder was moved or renamed.
There isn't enough free disk space for the processed copy.

One file failed but the rest finished: that's by design — a single failure never aborts the batch. Fix or remove that file and start it again.

The Music library won't load (macOS): allow access when macOS asks, and check System Settings → Privacy & Security for MP3Gain. Tracks protected by DRM can't be processed.

Files sound the same after processing: if the original level is already close to your target, the change will be subtle. Compare the input → output numbers on the row, or use the in-app playback to hear it.

Progress bar jumps to 100% instantly: very short audio files finish almost immediately. This is normal.

Window won't close (macOS): while a batch is running, MP3Gain asks whether to stop it before closing. Confirm to cancel everything and quit.

11. Glossary of Terms

Clipping: Harsh distortion that happens when audio exceeds the maximum digital level. Sounds like crackling or buzzing.
dB (Decibel): A unit for measuring sound level. In digital audio, 0 dB is the maximum, and negative numbers indicate how far below maximum. -20 dB is quieter than -10 dB.
EBU R128: A European broadcast standard for measuring loudness. It's designed to match how human ears perceive volume, not just the raw electrical signal. Used by TV, radio, and streaming services.
LUFS: "Loudness Units relative to Full Scale." The standard unit for perceived loudness. Streaming platforms often target around -14 to -16 LUFS. Lower (more negative) = quieter.
Loudness Range (LRA): How much the volume varies within a track. A classical piece might have wide range (quiet passages to loud crescendos); a pop song typically has narrow range.
Normalization: The process of adjusting audio so that multiple files play at a consistent volume level.
Peak: The single loudest moment in an audio file. Keeping peaks below 0 dB prevents distortion.
RMS (Root Mean Square): A mathematical way to measure the average level of an audio signal. A simpler, faster measurement than loudness, but less accurate to human perception.
True Peak: A more precise measurement of the absolute maximum level that accounts for what happens between digital samples. Important for preventing distortion on real playback devices.