Understanding Click and Crackle in Audio

Click and crackle artifacts are among the most common problems in audio recordings. Clicks are short, impulsive spikes — often caused by dust on vinyl, digital glitches, or plosives from a poorly placed microphone. Crackles, on the other hand, are a series of rapid, irregular transients that sound like a frying pan or radio static. They typically arise from degraded analog media (worn tape or vinyl), dirty connectors, or DC offset in digital systems. Both degrade the listening experience, especially in quiet passages or with headphones, making removal essential for professional-sounding audio.

iZotope RX is the industry standard for repairing these issues. The software uses advanced spectral analysis and machine learning to isolate and remove unwanted transients without harming the signal’s integrity. Unlike simple noise gates or equalizers, RX’s algorithms target the specific spectral footprint of clicks and crackles, allowing for transparent restoration. This article walks you through a complete workflow — from initial analysis to final polishing — so you can achieve clean, natural-sounding results every time.

Preparing Your Workflow in iZotope RX

Before diving into processing, set up a clean session. Open iZotope RX Audio Editor (standalone) or use the app as an AudioSuite processor within a DAW. For detailed visual editing, the standalone version is preferable because it offers the full spectral display and all repair modules.

  1. Import the audio file — Drag a WAV, AIFF, FLAC, or even a high-resolution file directly into the workspace. iZotope RX supports sample rates up to 192 kHz, so high-res audio poses no problem.
  2. Make a backup — Before any processing, save a copy of the original. In the standalone editor, use File > Save Copy As… or duplicate the file in your operating system. RX processes are often destructive, and while you can undo steps, a backup ensures you never lose the source.
  3. Audition the problematic sections — Play through the audio and make note of where clicks and crackles occur. Use the transport controls and set a loop around a troublesome area. You can also use the Selection tool to isolate a few seconds for testing.
  4. Inspect the spectrogram — Clicks appear as bright vertical lines in the spectral display. Crackles look like scattered, noisy smudges across frequencies. Understanding this visual signature helps you choose the right tool and adjust parameters.
  5. Enable real-time preview — Always keep the Preview button active. It lets you toggle between processed and unprocessed audio, making it easy to hear whether the repair is working without committing to a permanent change.

Once your session and file are prepared, you can move on to the primary tool for click removal: the De-click module.

Step-by-Step De-click Module

The De-click module is specifically designed to detect and remove impulsive clicks, ticks, and pops. It works by scanning the waveform and spectrogram for short-duration transients that exceed a certain threshold relative to the surrounding signal.

Accessing the Module

In the Audio Editor, select the area you want to repair (or leave it unselected to process the entire file). Then open the De-click module from the Repair menu in the top toolbar. The interface shows a waveform preview and several sliders.

Key Controls

  • Sensitivity — Controls how aggressively the module detects clicks. Higher values catch smaller and quieter clicks, but may also trigger on desired transients like consonants or percussion. Start at 50% and increase gradually.
  • Strength — Determines how much attenuation is applied to detected clicks. A lower value leaves some residual click, while a high value can remove all energy, potentially causing an audible reduction in high-frequency content. Typically, a value between 40% and 70% works well.
  • Filter Click — When enabled, applies a mild lowpass filter to the click region after removal, making the repair sound smoother. Leave this on for most non-musical material.
  • Artifact Control — Adjusts how much residual noise is left after processing. A lower setting removes more but can sound artificial. For dialogue or voiceovers, keep it around 30%.

Workflow for De-click

  1. Set a short loop (2–5 seconds) around an area with obvious clicks.
  2. Start with Sensitivity around 40% and Strength around 50%.
  3. Press Preview to hear the repaired version. Toggle between original and processed using the A/B button in the preview section.
  4. If clicks remain, increase Sensitivity. If the audio sounds dull or “squashed,” lower Strength or decrease Artifact Control.
  5. Once satisfied, click Process. Be aware that processing the entire file may take a few seconds. If you only processed a selection, the changes apply locally.

For very dense clicks (e.g., a badly scratched record), you may need to process the same section at multiple passes with different settings. Always start conservatively and increase only as necessary.

Deep Dive into Spectral Repair for Crackles

Spectral Repair is iZotope’s most powerful tool for removing non-uniform noise like crackles and electrical hums. Unlike De-click, which works in the time domain, Spectral Repair operates in the frequency domain, letting you “paint” over problematic regions in the spectrogram.

Selecting the Problem Area

Use the Selection tool (the rectangle icon) to draw a box around the crackle in the spectral display. Drag over the exact frequency range and time duration where the crackle appears. For scattered crackles, make multiple selections by holding Shift while drawing.

Choosing the Right Mode

  • Attenuate — Reduces the level of the selected region. Best when you just need to lower crackle intensity without removing it entirely. Use a Reduction amount of about -20 dB initially.
  • Replace — Completely removes the selected area and fills it with synthesized noise based on surrounding audio. Excellent for isolated crackles and pops, but can sound unnatural if the region is too large or in complex music.
  • Fill — Similar to Replace but uses only the data from the edges of the selection. Works well for short, narrow crackles in sustained tones or room tone.
  • Attenuate with Surrounding — Blends the attenuated signal with the surrounding frequencies. Good for crackles that overlap desired signal content.

Using the Spectral Repair Step by Step

  1. Zoom into the spectrogram until you can clearly see a crackle (often a bright yellow or red streak).
  2. Select the region with the rectangle tool. Keep the selection as tight as possible — don’t include clean audio.
  3. Open Spectral Repair from the Repair menu.
  4. Choose Attenuate as a starting point. Use a reduction of -15 to -25 dB.
  5. Click Preview. If the crackle is still audible, try increasing reduction or switching to Replace.
  6. If you hear artifacts (like a warble or wobbly tone), increase the Window Size or switch to Attenuate with Surrounding.
  7. Apply processing. Repeat for each crackle region.

Spectral Repair requires a careful hand. It’s best used on isolated events rather than continuous noise. For continuous crackle, combine it with the De-crackle module (covered next).

Combining Modules: De-crackle, De-noise, and More

Professional restoration rarely relies on a single module. Combining them yields the cleanest results while preserving natural sound. Here’s a logical chain to follow.

De-crackle Module

The De-crackle module targets rapid, repeating crackle that sits in the low-to-mid frequencies (2–8 kHz). It is especially effective on tape hiss with added crackle or digitally clipped transients. It works similarly to De-click but focuses on multiple events per second. Adjust Number of Clicks and Sensitivity to match the density of your crackle. Use the Reduction slider carefully — too much can make speech sound thin.

De-noise with Adaptive Mode

After removing transients, use De-noise to clean up residual background hiss or hum. Take a noise print from a silent section (a few seconds of pure room tone) and let RX analyze it. Then adjust Reductions to around 15–20 dB for broadband noise. Enable Adaptive Mode if the noise floor changes over time.

Order of Operations

  1. De-click — Remove impulsive clicks first. They are easiest to spot and affect the perception of other noise.
  2. De-crackle — Then address rhythmic crackle. This module can sometimes remove low-level clicks missed by De-click.
  3. Spectral Repair — For stubborn, visible crackles or pops that remain.
  4. De-noise — Finally, apply noise reduction to clean the overall floor. Doing noise reduction after transient removal prevents the noise suppressor from treating clicks as signal and trying to preserve them.

Always monitor the Residual signal (the part being removed) to ensure you’re not pulling out desired frequencies. In De-noise, for example, click the Residual button to hear only what will be removed. If you hear clear voice or music in the residual, you’re over-processing — dial back the reduction.

Advanced Tips for Professional Results

Moving beyond basic usage, these techniques separate amateur fixes from professional restoration.

Work with Multiple Passes

One aggressive pass of De-click often creates digital artifacts (especially on vocal sibilance). Instead, make two or three passes with lower settings (Sensitivity 30%, Strength 40%). This removes clicks in layers and leaves the sound more natural. Between passes, listen carefully for any new artifacts.

Use the Frequency Selection Tool

Sometimes crackles only appear in a narrow frequency band — like an 8 kHz hiss on old cassettes. In the De-click or De-crackle module, you can limit processing to a specific frequency range by enabling the Frequency Range option. Drag the brackets on the spectral display to define the band. This prevents the module from affecting bass frequencies or vocals that are click-free.

Keyboard Shortcuts for Speed

Learn a few keyboard shortcuts to speed up your workflow:

  • Spacebar — Play/Pause selection
  • Shift + C — Loop selection
  • Tab — Jump to next module in the list
  • Ctrl + Z / Cmd + Z — Undo
  • Ctrl + Shift + Z / Cmd + Shift + Z — Redo

Batch Processing with RX Editor

If you have multiple files (e.g., an entire podcast episode or album), use the Batch Processor in RX Editor. Drag in all files, add modules in the same order, and apply uniform settings. You can adjust parameters per file by clicking the gear icon. This saves hours for repetitive tasks.

Preserve Transients with “Transient Detection”

In both De-click and De-crackle, there’s a hidden Transient Detection tab. Here you can set a threshold for what constitutes a click versus a musical transient. For drum recordings, raise the Max Duration setting so that short snare hits are not mistaken for clicks. For speech, keep it low to suppress unwanted pops.

Common Pitfalls to Avoid

Even experienced engineers can fall into traps. Watch out for these common errors.

Over-processing with Spectral Repair

Using Spectral Repair on large areas (more than 1 second) or on dense musical content often produces “hole” artifacts — moments where the audio sounds muffled or artificial. Always use the narrowest selection possible and choose Attenuate before Replace.

Relying Only on De-click for Crackle

De-click is excellent for isolated clicks, but it struggles with continuous crackle. The module is designed for events that are shorter than 10 ms. Try De-crackle first for sustained crackling sounds.

Processing at Full File Without Preview

It’s tempting to click “Process” and walk away, but applying global settings to a long file can ruin sections. Loop through different parts (beginning, middle, end) with preview to ensure the repair is consistent. Uneven noise floors or varying levels can cause the modules to behave differently.

Ignoring Phase and Sample Rate Settings

When processing in a DAW via AudioSuite, make sure your session sample rate matches the source file. Mismatches can cause aliasing or shift the timing of transient removal. In RX standalone, always set the output format to the original sample rate and bit depth (e.g., 48 kHz / 24-bit).

Forgetting to Check Phase in Stereo Files

Clicks in a stereo track can be only in the left or right channel. If you process both channels identically, you may increase phase misalignment. Use the Split Stereo feature in RX to process each channel separately, then combine. Alternatively, enable Linked in De-click’s channel control to process both channels together but detect clicks independently.

Bringing It All Together

Professional click and crackle removal is a skill that balances precision with restraint. iZotope RX provides all the tools you need, but the real craft lies in knowing when to apply each one and how much is enough. Start with the loudest artifacts, use the proactive modules (De-click, De-crackle), then refine with Spectral Repair, and finish with light noise reduction. Always compare your repaired audio to a reference — whether it’s the original problematic file or a clean recording from a similar source.

Practice on a variety of materials: vinyl rips, dialog from vintage films, or field recordings. Each will teach you how the modules react to different transients. For further reading, consult iZotope’s official documentation for module-specific details, or explore the Sound On Sound guide to audio restoration for deeper theory. With patience and a methodical approach, you’ll soon be able to lift clicks and crackles from any recording, leaving only the clean, professional sound your audience deserves.