iZotope RX Selections, Preview, Compare and History

In the RX Audio Editor, turn Instant Process off before drawing a selection. Audition the target, try module settings with Preview and Compare where available, then render one approved result. Use History to revisit committed edits and save an RX Document when that edit trail needs to survive closing the file.

Play Selection Only and Preview answer different questions. The first auditions the selected part of the current audio state without adding module processing; it does not recover an untouched original after earlier renders. Preview auditions the active module, Compare holds candidate settings, and Undo History records committed changes.

This guide covers the standalone RX 12 Audio Editor in Standard and Advanced. Elements has plugins rather than this Editor workflow; the current edition comparison confirms that distinction. RX plugins and modules loaded inside Module Chain do not have the individual Editor footer controls described here, except plugin Bypass. See the Editor, plugins and RX Connect guide if the window in front of you looks different.

The complete RX decision loop

RX 12 gives this loop more room with a larger spectrogram and resizable History panel, according to the current RX 12 feature overview. The tools still require editorial judgment: the smallest visible selection is not always the smallest selection that sounds natural.

Choose the selection from the defect shape

Time Selection covers a horizontal time range across the file. Use it when the entire spectrum needs the same operation: a clipped phrase, a gain change or a short section of steady noise.

Time-Frequency Selection draws a rectangle constrained in both dimensions. It suits a whistle, a narrow buzz burst or one visible event that occupies a known band.

Frequency Selection selects a band across time. Use it for diagnosis or processing that belongs to a persistent range, but avoid assuming every signal in that band is unwanted.

Lasso follows an irregular outline. Brush paints regions with an adjustable diameter; hold its toolbar icon to change the size, or use Ctrl/Command with the mouse wheel while Brush is active. Magic Wand first selects the strongest tone under the cursor. Clicking an existing selection with it adds related harmonics. These operations are documented in the current RX 12 selection-tool reference.

Shortcuts speed work only after the selection is right

The documented defaults are T for Time, R for Time-Frequency, F for Frequency, L for Lasso, B for Brush and W for Magic Wand. Confirm the current menu if you use a customized key map or a newer operating-system layout.

These are Editor defaults, not the shortcut map for the separate RX Spectral Editor ARA plugin. For numerical precision, edit the selection start/end/length and frequency-boundary readouts below the spectrogram. Check the selected channels as well as the time and frequency range before applying a repair.

Shift builds an additional area into the active selection. Alt or Option can subtract from it. With Magic Wand, adding another related harmonic can be faster than drawing a broad box that includes unrelated speech or music.

Selection size and edge softness are separate decisions. Keep the defect inside the processing region, then use Selection Feathering for transitions across time and frequency. Shift-F toggles feathering; Alt/Option-F opens its controls. More feathering makes a longer crossfade, which can soften an edge but also blend more of the untreated defect back in. Listen to the boundary instead of assuming a wider or softer selection is always better.

Use the spectrogram and waveform together

The spectrogram reveals frequency shape; the waveform reveals level, timing and clipping. A mouth click may be a thin vertical impulse in both views. Hum becomes horizontal spectral rails that the waveform alone may hide. A clipped peak is obvious in the waveform even when its spectral energy looks broad.

Zoom until the event has a recognizable boundary, but keep enough surrounding audio to understand it. The RX spectrogram tutorial maps color, harmonics, impulses and broadband texture before you choose a tool.

Do not select from appearance alone. Listen before and after the event. What looks like a narrow unwanted tone may be part of a sustained note; what looks like noise may be breath that carries a word.

Play Selection Only before opening a module

Play Selection Only auditions the selected time and frequency region in the current edit state. It answers a diagnostic question: did you capture the buzz, click or resonance you meant to repair? The current RX transport reference distinguishes this from ordinary playback. Turn Instant Process off first: with it enabled, the new selection can already have triggered a repair before you audition it.

Turn on Loop when a short target needs repeated listening. A narrow frequency selection may sound unlike normal playback because you are hearing only part of the spectrum. That is useful for identification, not a preview of the final audio.

Move the playhead without discarding a complex selection by holding the documented Ctrl or Command modifier. This lets you start before the repair, hear the transition and retain a carefully drawn lasso or brush region.

Nine steps from selection to reversible edit

1. Preserve the source. Work on an independent audio copy and keep the original separate. Save an RX Document checkpoint if the file already contains approved repairs.
2. Prepare the selection. Turn Instant Process off, choose a tool that fits the defect and confirm the intended file tab, channels and selection bounds.
3. Add listening context. Use pre/post-roll or ordinary playback around the target without unnecessarily enlarging the area to be processed.
4. Audition the target. Use Play Selection Only and Loop to hear the selected content of the current edit state before adding the next repair.
5. Preview the module. Where available, audition settings and bypass on a fixed selection. Check that any removed-signal listening mode is off for normal output.
6. Create named candidates. Send different settings to Compare on the same pre-repair audio and selection. Double-click list items to name their purpose.
7. Choose at matched loudness. Compare the candidates against the pre-repair reference, preserving wanted detail and checking surrounding context.
8. Render once and replay. Undo all test renders for this repair or reopen its saved pre-repair checkpoint, restore the selection and apply the winning settings once. Check boundaries and output peaks.
9. Preserve history and delivery. Name useful History states, save an RX Document, export approved audio to a new filename and reopen both files to verify the intended result.

Use this decision loop with the supported controls for De-click, De-clip, denoising or spectral repair. Some modules offer Compare without real-time Preview. Missing Preview is not by itself a fault, and a module-specific listening mode may output removed material instead of the repaired signal.

Preview tests controls without committing the edit

Where supported, module Preview auditions current settings without committing them. It normally uses the active selection; with no selection it starts at the playhead. Ctrl/Command-clicking to move the playhead while retaining a selection can also deliberately start Preview earlier for context. A start outside the highlight therefore does not always mean that your selection was lost.

The RX 12 Common Module Controls guide documents Shift-Space for Preview and Shift-B for Bypass. Use the named buttons if your shortcuts are customized. Controls can change during Preview, but allow the current buffer to play through before judging the new value.

Bypass frequently and level-match the impression. A reduction module can sound better merely because it is quieter; Enhance or Gain can win because it is louder. Judge the disappearance of the defect against preserved speech, transients, stereo image and room continuity.

Preview buffer, loop and pre/post-roll

Preview can buffer CPU-intensive processing before playback. The + button beside Preview opens Preview Options, including buffer length; the portion being prepared is tinted red in the spectrogram. Buffering changes when you hear a result and is not, by itself, evidence of reduced audio quality. Follow the chosen module's documented mode restrictions and verify the rendered audio rather than assuming either identical or inferior quality for every module.

Loop helps expose unstable behaviour across repeated playback. Pre- and post-roll add unprocessed context around the selected repair. In Preferences > Misc, set the pre/post-roll duration to suit the material; the module-controls manual describes one second on each side by default and up to ten seconds. Setting the values to zero disables this context. Check timing at the actual edit boundary, not only in a repeating isolated fragment.

For a click, a short loop may be enough. For dialogue denoising, include the preceding room tone and the following word ending. For music, cross the bar line so the repair's effect on groove and sustain is audible.

Compare is for different hypotheses, not tiny knob changes

Compare prepares the result of a module's settings in the background and adds an item to its list. Keep the same input state, channels and selection when making alternatives. A candidate calculated after a test render answers a different question: it is another processing stage on changed audio. Return to the pre-repair state and rebuild the candidates if that happens.

Name candidates by intent: “light click only,” “less reduction,” or “higher quality, lower reduction.” Double-click a list item to rename it. Select an item and click Preview in the Compare window to audition it. View Settings recalls that item's controls without applying them; Render commits the selected settings. Check which item is selected before using either button.

Use no more candidates than you can evaluate reliably. Three distinct approaches are usually more informative than twelve nearly identical strengths. If none is clean, change the selection or the module—not just another decimal value.

If Compare is unavailable, check the view before troubleshooting the installation. Composite view does not support Compare and applies edits to all its included files. In RX 12 All Stems view, Compare is also unavailable; select an individual stem in the tab header to use it. Exit Composite view for a single-file comparison. These limits are separate from whether a particular module supports Preview.

What to compare besides cleanliness

• Wanted detail: consonants, pitch, transients and breath remain intact.
• Transitions: no click, hole or room-tone jump appears at the boundary.
• Artifacts: no chirp, metallic residue, gating or phase smear is introduced.
• Context: the repair works in the full sentence, scene or mix.
• Efficiency: the setting solves the defect without requiring another repair for its side effects.

The waveform and spectrogram can help explain a difference, but they do not rank sound quality by themselves. A visually empty gap can be worse than a quiet, stable ambience bed. For broad tool choice, see the background-noise guide.

Render one winner, then listen again

Before committing, return to the exact state used to build the winning candidate. If you made test renders for this repair, undo all of those tests or reopen the saved pre-repair checkpoint; preserve earlier approved work. Restore the intended selection, turn any removed-signal listening mode off and render the winner once. Replay the result and check output peaks, because level matching during audition does not guarantee delivery headroom.

Then listen from farther back. A repair that sounds convincing in a tiny loop can interrupt the rhythm of a sentence or the decay of a note. If it fails, undo that repair. If later good work must stay, the local Restore Selection operation below can recover an earlier version of just the affected region.

Do not stack the next module until the current render passes. Once several repairs accumulate, cause and effect become harder to separate.

Undo, History and Restore Selection solve different problems

Undo moves back through actions; the History panel exposes their timeline. Click an earlier History state to revisit the file at that point. Drag the handle above the panel to resize it, and double-click an entry to rename it. Clip Gain and Module Chain edits may appear grouped under their respective parent entries.

Restore Selection is local. Keep the current file state active and select the region to recover. Hover over the desired earlier row in History, then click the Restore Selection icon that appears beside that row. This restores the selected area to that point while leaving the rest of the current file alone. Clicking the historical state itself is the broader rollback operation. The current Undo History manual describes the icon-based action.

For example, if a later denoise pass damaged one word, select that word in the current state and use the icon beside the state before denoising. Audition the recovered word and its joins with the surrounding processed audio. This recovers all changes to that region since the chosen state; it does not selectively remove one named module while retaining every later edit inside the same region.

Timing edits need extra care. In a 2024 discussion of RX 10/11 History, a user reported restoration from the wrong location after deleting earlier audio. That is an older user report, not a reproduced RX 12 defect. Keep a checkpoint before deleting or inserting time and verify alignment on a copy before relying on local restoration across those changes.

Selection recall is another separate feature. With Recall selections during undo/redo enabled in Preferences > Misc, stepping through History recalls the selection associated with that edit. Disable it when you need to preserve a fixed listening selection across states. Restoring selection bounds is different from Restore Selection, which restores audio inside the bounds.

Saving audio is not the same as saving the edit trail

An exported WAV contains the current audio state, not a navigable History. Use File > Save RX Document to retain the original audio, edits, most recent selection and view state. RX Documents open in the RX Audio Editor; they are not delivery audio for a DAW. Reopen the saved document and inspect its History before considering the archive complete.

The current manual documents File > Export History as XML as a separate record of the RX version, date/time, corrected file, channels, sample rate/bit depth, edit parameters and selections. If your installed edition does not expose that command, retain the RX Document and written processing notes. An XML log contains instructions and metadata rather than the audio needed to reverse a repair; it does not replace the source or RX Document.

Keep three layers for important work: untouched source, RX document with history, and approved delivery render. History is powerful inside the session; it is not your only backup.

For delivery, choose File > Export and a new filename. Ordinary Save overwrites an open WAV or AIFF on disk; a duplicated DAW region may still point to that same file. Export Selection delivers only the selected excerpt. Reopen the exported audio and check duration, channels, alignment and peaks in its destination.

Common workflow failures

Preview changes too much audio. Stop and inspect the tab, channels, selection and view. With no selection, playback starts at the playhead; Composite view can affect multiple files. Use Play Selection Only to diagnose the target after confirming Instant Process is off.

The loop sounds fine but the edit clicks. Add listening context, inspect the selection boundary and adjust feathering conservatively. Recheck the actual rendered transition.

Compare candidates all sound the same. Create distinct hypotheses or level-match them. Tiny changes below audibility do not help.

History is unreadable. Rename decision points before the list becomes long.

Undo removed good later work. Return to the latest intended state, make the local selection and click the restore icon beside the desired earlier row. Do not simply navigate the whole file back again.

The reopened WAV has no history. Preserve an RX document; an audio export is a finished state, not the editor session.

Final editor quality gate

• The selection contains the defect and no unnecessary healthy audio.
• Play Selection Only confirms the target before a module opens.
• Preview is checked with bypass, loop and useful context.
• Compare candidates represent different approaches and have descriptive names.
• The chosen result wins at matched loudness.
• The winner is rendered once, with normal output selected, then checked for audible boundaries and output peaks.
• Important History states are named; local restore is checked against the intended earlier state and timeline.
• The untouched source and RX document are preserved where the project requires them.

The practical test is whether you can explain what changed, hear why it helped and return to the right earlier state if it did not. Continue through the Learn iZotope RX hub for interface, spectrogram and first-repair fundamentals.

Frequently asked questions

What is the difference between Play Selection Only and Preview?

Play Selection Only auditions the selected content of the current audio state without adding module processing. Preview auditions supported module settings without committing them. Neither automatically returns previously rendered audio to the untouched original.

What does Compare do in iZotope RX?

Compare processes multiple settings as separate candidates so you can audition them side by side, inspect their controls and render one selected result.

Which RX selection tool should I use?

Match the shape: Time for a whole-spectrum event, Time-Frequency for a rectangle, Frequency for a persistent band, Lasso for an outline, Brush for small painted regions and Magic Wand for related harmonics.

Why does Preview start outside my repair?

With no active selection, Preview starts from the playhead. Pre/post-roll or deliberately moving the playhead with Ctrl/Command while retaining the selection can also start playback outside the highlight. Inspect both the selection and the listening context.

Is RX Preview the same quality as Render?

Check the specific module and mode. A preview buffer alone does not imply reduced quality, and some modules do not support Preview. Render the chosen settings once and listen to the result before approval.

Can I restore one word without undoing later edits?

Yes. Select the word in the current state, hover over the desired earlier History row and click its Restore Selection icon. Audio outside the selection stays current; inside it, all changes since that earlier state are replaced. Check boundaries and alignment.

Does saving a WAV keep RX Undo History?

No. A WAV stores the rendered audio. Save an RX document when you need the edit history to remain available.

How many Compare candidates should I make?

Make only enough to test distinct approaches—often two or three. Name them by purpose and change the selection or module if none solves the defect cleanly.