Free online tool

Bulk Slowed Reverb Converter

Convert a whole album to slowed + reverb at once. Shared speed, reverb and bass settings, per-track subsets, one ZIP of MP3s. Free, in-browser, no upload.

Open the free editor: upload MP3, WAV, AAC, OGG or FLAC, adjust speed, reverb, bass, tone, width and space, then export MP3 or a ZIP of many tracks. Everything runs in your browser.

A bulk slowed reverb converter takes a stack of songs and gives you back a stack of slowed versions that all sound like they belong to the same project. That is the job this page is built for. The editor above is the same one you get on the slowed reverb maker page, but here the focus is on moving a whole album through it in one sitting rather than one track at a time.

Everything runs locally in your browser. Twenty files or two hundred, none of them leave your computer. There is no upload queue, no per-file limit and no account. The only resource you spend is your own CPU time, which matters when you are deciding whether to run a batch on a laptop or a phone, and that is covered below.

If you have never made a single slowed edit before, read the step by step guide first, then come back. If you already know the sound you want and need to apply it to forty tracks, keep reading. The batch processing guide goes deeper on building a repeatable routine around this page.

Why batch matters for slowed channels

A slowed channel lives on volume and consistency. One upload rarely does anything. A full album of slowed versions, posted on a schedule with matching artwork, is what the algorithm and the listeners both respond to. Doing that one song at a time means loading a file, setting six sliders, exporting, and repeating the whole dance thirty times. You will drift. Track four ends up at 0.84x, track nine at 0.81x, and the album no longer feels like one thing.

Batch processing fixes the drift because the settings are set once. It also saves the mental overhead of remembering what you did. The settings live on the selected tracks, and you can see them while you work.

The album-at-once workflow

Here is the sequence that works best, in order.

1. Add every file at once. Drag the whole album's worth of MP3, WAV, FLAC, AAC or OGG files onto the editor, or use the picker and multi-select. Each file appears as its own track in the list.
2. Click Select All Tracks. From this point, every slider move applies to all of them. Pick a preset as the starting point. For a deep, dark album sound choose Haze Chamber. For something lighter choose Wave Drift.
3. Audition on two or three tracks. Play the busiest song on the album, then the sparsest. If both sound right at the same settings, the whole album will. If not, you will handle exceptions in the next step.
4. Make subsets for the exceptions. Click Clear Selection, then select only the tracks that need a different treatment. Change the sliders. Only those tracks update. Everything else keeps the album settings.
5. Download All. The editor renders each track through the same chain you previewed (with Preserve pitch off; with it on, the export will be pitch-shifted) and encodes each to MP3 in a web worker, then packs the results into a single ZIP.

The preview and the export use the same signal chain, so you are not guessing. What you heard in step three is what every file in the ZIP sounds like.

Shared settings versus per-track settings

It helps to think of the track list as having two modes.

With Select All Tracks on, the editor behaves like a single global effect. This is the right mode for most album work. Speed in particular should almost never vary across an album, because listeners notice tempo and key shifts between consecutive uploads far more than they notice reverb differences.

With a subset selected, the editor behaves like per-track processing. Common reasons to use it:

• A track with dense vocals needs Reverb pulled down from 50% to 30% so the words survive.
• An instrumental interlude can take more Space and more Reverb than the vocal tracks.
• A track that already has heavy sub bass needs Bass at +3 instead of +8 to avoid distortion on phone speakers.
• A spoken intro skit should probably stay close to Dry so it stays intelligible.

Select the exception, adjust, then click Clear Selection. Later, if you want to check what any track is set to, select only that track and the sliders show its values.

What you get back

Output naming is predictable, which matters when you are about to drop thirty files into a video editor.

Every file inside the ZIP is an MP3 at 96 kbps, 32 kHz. There is no WAV option and no higher bitrate option. That bitrate is chosen so the encoder can run fast inside a browser tab, and it is fine for YouTube, TikTok and Shorts, all of which re-encode whatever you upload. If the goal is a distribution master rather than a video upload, process a WAV source and finish in a DAW. The export bitrate guide explains why this is less of a compromise than it sounds.

If you plan to rename files for upload, the naming and packaging guide has a system that works for both YouTube titles and sale bundles.

Settings that hold up across an album

An album batch needs settings that flatter the average track rather than the best one. These are starting points.

Pick one row, apply it to everything, then fix the two or three tracks that break. That order is faster than tuning each track from scratch and gives a more coherent result.

How long a batch takes

Rendering happens faster than real time, but it is still real work, and the hardware you are on sets the pace. Three things decide the total time: the number of tracks, the length of each track, and the CPU of the device.

On a laptop or desktop, an album batch is comfortable. The encoder runs in a worker so the page stays responsive, and you can keep adjusting settings on one subset while waiting. On a phone, the same batch takes noticeably longer. Phones have slower CPUs, less memory headroom, and browsers that throttle tabs when the screen locks or you switch apps. A ten track album on a phone is doable. A forty track batch on a phone is possible but tedious, and you should keep the screen on and the tab in front until the ZIP download appears.

Practical advice: if you own both, use the laptop for batches and the phone for one-off edits. If you only have a phone, split large catalogues into groups of five to ten tracks. The result is identical either way, because the processing chain does not change between devices. The phone guide covers the mobile side in detail.

Memory and very large batches

Each decoded track lives in browser memory as uncompressed audio while it is loaded. A long album of WAV files uses far more memory than the same album as MP3, because the browser decodes everything to the same raw format regardless of the source. If the tab becomes sluggish or the browser warns about memory, Delete Selected the tracks you have already exported and load the next group. The ZIP you downloaded is already on disk, so clearing tracks from the editor loses nothing.

What the bulk converter does not do

It does not merge tracks into one file, add crossfades or gaps, trim intros, or export anything except MP3. It does not add metadata tags beyond what the encoder writes. It also does not independently shift pitch; pitch follows speed unless Preserve pitch is on, in which case the key is kept while the tempo changes in the preview. Preserve pitch changes the live preview only; exported files keep the speed-linked pitch. For stutters, chops or scratches you need a DAW.