Recording high-quality audiobooks for ACX (Audiobook Creation Exchange) requires clear, professional audio with minimal background noise. ACX has strict technical specifications for noise floor, RMS levels, and overall clarity. Consistent background noise reduction is essential to meet those standards and to deliver a listening experience free from distracting hums, hisses, or room echoes. This guide covers best practices to achieve reliable, repeatable noise reduction across all your recordings, from pre-production through final mastering.

Understanding Background Noise Sources in ACX Recordings

To reduce noise effectively, you must first identify its origins. Background noise in home studio recordings typically falls into three categories:

  • Environmental noise: Traffic, HVAC systems, appliances, computer fans, and outdoor sounds. These noises are often intermittent or low-frequency.
  • Reverberation and room reflections: Hard surfaces like bare walls, floors, and windows cause echoes and comb filtering, which muddy the recording and create a hollow sound.
  • Electronic noise: Hum from poorly shielded cables, ground loops, or interference from nearby electronics (e.g., monitors, routers, dimmer switches).

Each type requires a different mitigation strategy. While some noise can be removed in post-production, the best approach is to minimize it at the source. ACX requires a noise floor of at least -60 dBFS (preferably lower), so a clean recording gives you more headroom for processing without introducing artifacts.

Pre-Recording Room Preparation for Optimal Noise Control

Soundproofing vs. Acoustic Treatment

Soundproofing blocks external noise from entering your recording space, while acoustic treatment controls reverberation inside it. For most home recordists, a combination of both works best. Start by sealing gaps under doors with draft stoppers, closing windows, and turning off noisy appliances (refrigerators, air conditioners, computers) during recording. For acoustic treatment, use heavy curtains, thick rugs, and strategically placed foam panels or bass traps to absorb mid and high frequencies. A reflection filter around the microphone can help isolate your voice from close reflections.

Measuring Your Noise Floor

Before recording, check your room’s noise floor using your audio interface and a microphone. In your DAW, create a new track and record a few seconds of silence. The RMS level of that silence (with no speaking) should be at least -60 dBFS or quieter. If it’s higher, identify the source (e.g., a ground loop hum) and address it. A portable spectrum analyzer app on your phone can help locate problem frequencies.

Consistent Equipment Setup Across Sessions

Variability in gear settings from day to day is a common cause of inconsistent noise. Follow these guidelines for repeatability:

  • Use the same microphone, interface, and cables for every session. Label your setup so you can replicate it quickly.
  • Set a fixed gain level. Mark the gain knob with a Sharpie or take a photo of your interface settings. For ACX, aim for peak levels between -6 dBFS and -3 dBFS, with average levels around -15 dBFS.
  • Keep the same microphone position. Measure the distance from your mouth to the mic (typically 6–12 inches) and maintain that distance. Use a pop filter and a floor marker for consistency.
  • Monitor with closed-back headphones to avoid bleed from headphone audio into the microphone. Avoid open-back headphones for recording.

If you must change equipment (e.g., a different microphone for a different narrator), recalibrate your noise reduction presets for that session.

Recording Techniques That Minimize Noise at Capture

Microphone Placement and Technique

Even with a quiet environment, poor microphone technique can introduce unwanted sound. Keep the microphone at a consistent angle (usually slightly off-axis to reduce plosives) and avoid handling the mic stand or cables. Use a shock mount to isolate the mic from floor vibrations. If you need to move or shift, do it between takes, not during.

Monitoring in Real Time

Wear headphones while recording and listen critically for any intermittent noise — a door slam, a car horn, a cell phone buzz. Don’t rely solely on the level meters; your ears can catch subtle sounds that meters miss. If you hear a problem, stop, fix it, and re-record that section. It’s far easier to capture clean audio than to remove a sharp transient noise later.

Controlling Plosives and Sibilance

Plosives (p, b, t sounds) and sibilance (s, sh) can create low-frequency pops and high-frequency hiss that may be mistaken for background noise or distortion. Use a pop filter and position the microphone slightly above or below your mouth line. Consider a de-esser plugin during post-processing, but only if sibilance is consistent.

Post-Processing Workflow for Noise Reduction

Creating an Accurate Noise Profile

In your audio editing software, select a segment of the recording that contains only background noise — typically 1–3 seconds of silence between takes or during a pause. This noise sample should be representative of the entire session: if environmental noise changes (e.g., a refrigerator kicks on), you may need multiple profiles. Most DAWs call this a noise print or noise sample.

Applying Noise Reduction

After capturing the noise profile, apply the noise reduction effect to the entire track. The key parameter is reduction amount (also called noise reduction dB). Start with a moderate value (12–18 dB) and listen critically. Too much reduction can cause a watery, “warbling” artifact, especially in quiet sections. Other important settings:

  • Sensitivity/Threshold: Controls how aggressively the algorithm discriminates between noise and speech. Lower thresholds catch less noise but preserve voice quality.
  • Frequency smoothing: Spreads reduction across neighboring frequencies to reduce artifact harshness. A moderate value (3–5 bands) often works well.
  • Attack/Release times: Faster settings reduce noise more aggressively but can clip transients. For speech, a medium attack (10–20 ms) and medium release (100–200 ms) are safe starting points.

Always preview the reduction on a short section before applying it to the whole file. Apply noise reduction as a non-destructive plugin or keep an undamaged backup copy.

Advanced Techniques: Spectral De-noising and Manual Editing

For stubborn noises that survive standard reduction, use spectral editing. In Adobe Audition’s Spectral Frequency Display or Audacity’s Spectrogram view, you can visually select and remove specific tonal noises (e.g., a 60 Hz hum, a high-frequency whine) with minimal impact on speech. Draw a selection around the offending sound and use the Silence or Remove tool. This is very effective for clicks, pops, and short broadband noises.

Software-Specific Noise Reduction Tips

Audacity

Audacity’s built-in Noise Reduction effect is free and capable. Steps:

  1. Select a noise-only section (1–2 seconds).
  2. Go to Effect > Noise Reduction and click Get Noise Profile.
  3. Select the entire track, reopen the effect, and set Noise reduction (dB) to 12–18, Sensitivity to 6–12, and Frequency smoothing (bands) to 3. Press OK.
  4. Listen carefully. If artifacts appear, undo and try lower sensitivity or reduction.

For hum removal, use the Notch Filter (Effect > Notch Filter) to target 60 Hz (or 50 Hz for EU) with a Q factor of around 30.

Adobe Audition

Audition’s Adaptive Noise Reduction effect is more advanced and adaptive. Select a noise profile section (Effects > Noise Reduction/Restoration > Capture Noise Print). Then apply the effect and adjust Noise Reduction (12–18 dB), Reduce by, and FFT Size (4096 is a good default). The Advanced tab lets you tweak spectral decay. Use the Spectral Frequency Display (View > Spectral Frequency Display) for manual removal of clicks and chirps.

Reaper

Reaper’s native ReaFIR plugin (FX > ReaFIR) can be used for noise reduction. Set mode to Subtract, then click Automatically build noise profile. Play a few seconds of silence while ReaFIR learns the noise. Then stop and switch to Subtract (noise reduction). Adjust the FFT size and threshold to minimize artifacts. For hum, use ReaEQ to cut narrow bands.

Ensuring Consistency Across Multiple Sessions

Save Noise Reduction Presets

Once you’ve dialed in a noise reduction setting that works for your room and voice, save it as a preset. In Audacity, click Save Preset; in Audition, save as a preset in the effects rack; in Reaper, save the plugin chain. Use the same preset for all chapters recorded in the same conditions.

Create a Recording Template

Most DAWs (like Reaper, Audition, or Studio One) allow you to save a project template with your track, effects chain (including noise reduction), input levels, and routing pre-loaded. This eliminates the risk of forgetting to apply noise reduction or using different settings between sessions.

Record a Test Tone or Room Tone at the Start of Each Session

Record 10 seconds of room silence (no speaking) before every recording block. This serves three purposes: it gives you a fresh noise profile that captures any changes in ambient noise, it acts as a reference for consistency, and it can be used to match noise reduction settings if you need to batch-process later.

Meeting ACX Technical Requirements for Noise Floor

ACX specifies that the background noise floor must be at or below -60 dBFS (RMS), with no hums, buzzes, or clicks. Use a RMS meter (e.g., Youlean Loudness Meter or your DAW’s native metering) to check silence sections. Also verify that your finished audio meets the specified -23 dB RMS loudness average and -3 dB peak limits. If your noise reduction is too aggressive, you may lower the noise floor but also degrade voice articulation, causing a “mushy” sound that fails ACX’s quality check.

Always run your completed file through a batch check against ACX guidelines: use tools like ACX’s official audio submission requirements page and third-party analyzers such as Audacity’s ACX checker plugin or the free Adobe Audition script for ACX.

Conclusion: Building a Repeatable Noise Reduction Workflow

Consistent background noise reduction in ACX recordings is not a single step — it’s a chain of decisions from room preparation to final processing. By controlling your recording environment, standardizing equipment and gain staging, capturing clean audio at the source, and applying a reliable post-processing workflow, you eliminate guesswork. Each chapter you produce will sound seamless and professional, maintaining the same low noise floor and clear vocal presence.

Invest time upfront in presets and templates. Save your noise profiles, document your microphone distance, and check your audio against ACX specs before submitting. With practice, noise reduction becomes an invisible part of your production, leaving listeners focused on the story — not the hiss.