PitchShifter

Transpose browser media, change its speed independently and add adjustable reverb — all isolated to the current tab. For Firefox desktop 140+ and Firefox for Android 142+.

🦊 https://addons.mozilla.org/en-US/firefox/addon/pitchshifter/ 🦊

Changelog

1.1.4

• Restores the media capture and playback-speed handling from 1.1.0, reverting the preventive capture filters introduced by the 1.1.1–1.1.3 hotfixes following reports that Pitch, Microtones and Reverb stopped working.
• Some cross-origin media can still become silent when effects are enabled. This original compatibility issue remains under investigation; see Limitations.

1.1.3

• Restores Pitch, Microtones and Reverb for YouTube videos using blob: URLs or MediaSource by removing the blanket native-audio fallback introduced in 1.1.2 (Users were reporting problems with this implementation).
• Retains the 1.1.1 protection for directly identifiable cross-origin media without a crossorigin attribute; those elements continue to use native audio and Speed.

1.1.2

• Follow-up to the 1.1.1 hotfix: YouTube video elements using blob: URLs stay on the browser's native audio path because the URL does not reveal whether the media is safe to route through Web Audio. Speed remains available with native pitch preservation; Pitch and Reverb are unavailable for those videos.

1.1.1

• Hotfix: avoids routing directly identifiable cross-origin media without a crossorigin attribute through Web Audio, preventing affected videos from becoming silent. Those elements stay on the browser's native audio path; Speed remains available with native pitch preservation, while Pitch and Reverb are unavailable for them.

1.1.0

• Per-tab On/Off control prevents PitchShifter from overriding media settings in other tabs, while guarding the selected speed when players reconfigure background media.
• AudioWorklet-based pitch and speed processing removes the previous visible delay and page-load crackling.
• Adaptive WSOLA/phase-vocoder speed processing keeps the configured pitch intact and reduces repeated-segment artifacts during slowdowns.
• A dedicated Reverb tab adds Simple and Advanced controls for amount, room size, decay, tone and pre-delay.

Features

• Real-time pitch shifting that keeps tempo, plus independent speed control whose pitch is compensated by the same SoundTouch engine.
• Separate Reverb tab with Simple and Advanced modes, stereo early reflections, a dense diffused tail and a smooth constant-power dry/wet mix.
• Hybrid SoundTouchJS engine: WSOLA in the normal range and a phase vocoder for smoother extreme slowdowns, with Lanczos interpolation in both.
• AudioWorklet processing keeps the DSP off the page thread, preventing page/DOM work from starving its audio callback.
• Works on supported HTML5 media, including pages with strict CSP (YouTube, etc.) and detached media elements used by players such as Spotify Web.
• Zero added latency when both pitch and speed are neutral: the audio goes straight through, as if the effect were off.
• Control values are remembered as presets, while activation is isolated to the current tab.
• Clean control-panel UI that follows your light/dark browser theme.

Controls

Click the toolbar icon to open the popup.

Control	Range	Step
Pitch	-12 to +12	1 semitone
Microtones	-1.00 to +1.00	0.01
Speed	25% to 200%	1%
Reverb	0% to 100%	1%
Room Size (Advanced)	50% to 150%	1%
Decay (Advanced)	0.8 s to 5.0 s	0.1 s
Tone (Advanced)	0% dark to 100% bright	1%
Pre-delay (Advanced)	0 ms to 100 ms	1 ms

Pitch, Microtones and Speed live on the front tab; Reverb has its own tab. Simple exposes only Amount and uses the tuned studio-room defaults. Advanced also exposes Room Size, Decay, Tone and Pre-delay while retaining the same Amount control. Pitch shift is (pitch + microtones) / 12 octaves and does not change tempo. Speed changes tempo while SoundTouch compensates the pitch. Each numeric control has a slider, -/+ buttons, direct entry and reset. Use the On/Off button to control only the current tab; moving any control turns it on for that tab. Turning it off restores the page's previous playback speed and pitch-preservation setting. Saved values remain available as presets, but a new or reloaded tab starts off so other sites keep their native media settings.

Install

1. Open about:debugging#/runtime/this-firefox.
2. Click "Load Temporary Add-on".
3. Select manifest.json in this folder.

Temporary add-ons are removed on browser restart. To keep it installed, package and sign with web-ext via addons.mozilla.org.

Development and releases

Pull requests to main are validated and packaged by GitHub Actions. After a merge to main, a new version in manifest.json automatically creates a v<version> tag and a GitHub Release marked as Latest, with pitchshifter-<version>.zip attached. Release notes come from that version's entry under Changelog above.

For each release, update manifest.json, add its Changelog entry, test the extension and merge to main. Already published versions are left unchanged; increase the version to publish another build. The workflow can also be rerun from the Actions tab. AMO signing and submission remain manual: download the ZIP from the GitHub Release and upload it to AMO.

The workflow uses standard GitHub-hosted runners and the built-in GITHUB_TOKEN; no additional secrets are required. It checks release rules, runs web-ext lint and verifies the packaged files. These checks do not replace testing audio effects in Firefox.

How it works

• injected.js runs directly in the page's main world via Manifest V3; content.js relays messages between the popup and the page.
• injected.js captures each media element with the Web Audio API and coordinates its routing. The official SoundTouchJS 2.1.1 worklets run WSOLA and phase-vocoder processing on the browser's audio render thread.
• Both worklets are packaged as web-accessible extension resources. Their extension URLs are supplied by content.js, so they load without depending on the host page's scripts.
• When no compensation is required, the element is wired straight to the output and the shifter is taken out of the path entirely — no buffering and no added latency.
• Speed is applied as the element's playbackRate with native pitch preservation disabled. Pitch and playback rate are mirrored to separate worklet AudioParams; SoundTouch divides the requested pitch by playback rate internally, so Speed does not alter the configured pitch.
• Rapid slider input is coalesced to one update per visual frame. Pitch changes use a short 40 ms parameter ramp; playback-rate compensation is applied immediately so Speed cannot leak into audible pitch.
• WSOLA uses a low-latency profile at normal speeds and tempo-aware windows with a longer overlap below 70% Speed; it returns to low latency above 76% to prevent profile oscillation. Below 45% the phase vocoder is selected automatically, and WSOLA returns only above 55%. A warmed-up 50 ms crossfade hides every processor/profile switch.
• Reverb runs after the pitch engine, so an engine crossfade does not restart its tail. The generated stereo impulse combines asymmetric early reflections, a 12-line feedback delay network and frequency-dependent late decay. Advanced Room Size and Decay changes create a cached impulse and crossfade between convolvers over 120 ms; Tone and Pre-delay use smoothly automated realtime nodes. Reverb DSP is created lazily and removed from the input path at 0%.
• The popup reads and writes state through the content script. Values are saved to storage.local as presets, but the enabled state remains local to the current tab and is never applied automatically elsewhere.

Limitations

• Cross-origin media without a successful CORS-enabled request can become silent when routed through Web Audio. Version 1.1.4 restores the capture behavior of 1.1.0, so affected media is no longer excluded automatically. If this happens, turn PitchShifter off and reload the page to restore native playback.
• Each processing engine needs a short amount of audio before producing output. The phase vocoder makes very slow playback smoother, but difficult material can still exhibit some frequency smearing. With pitch at 0 and speed at 100%, there is no added latency.

Credits

• Pitch engines: SoundTouchJS AudioWorklet and Phase Vocoder Worklet 2.1.1 by Steve “Cutter” Blades, based on the original work by Olli Parviainen et al. The bundled processors are available under MPL-2.0; see soundtouch-worklet.LICENSE.txt.
• UI typeface: IBM Plex Sans, SIL Open Font License 1.1 (see popup/fonts/OFL.txt). Bundled as a latin subset.

License

Copyright (c) 2026 daffwt221. All rights reserved (see LICENSE). Bundled components keep their own licenses: SoundTouchJS AudioWorklet (MPL-2.0) and IBM Plex Sans (SIL OFL-1.1) — see Credits.

Files

File	Role
manifest.json	Manifest V3; storage; popup plus isolated/page-world content scripts on all frames.
popup/	Popup UI (popup.html, popup.css, popup.js) and bundled font in popup/fonts/.
content.js	Bridge between popup and page; keeps activation isolated to the current tab.
injected.js	Page-world media capture, state, and Web Audio routing.
soundtouch-worklet.js	Bundled SoundTouchJS 2.1.1 WSOLA processor running on the audio render thread.
phase-vocoder-worklet.js	Bundled SoundTouchJS 2.1.1 phase-vocoder processor for extreme slow speeds.
soundtouch-worklet.LICENSE.txt	MPL-2.0 notice and upstream source for the bundled processors.
icons/icon.svg	Toolbar icon / logo.