• Written by: admin
• 02/02/2025

ACX Noise Floor Explained, How To Lower It Without Wrecking Your Voice

A quiet background is the foundation of an easy-to-listen audiobook. Most platforms, including ACX, expect a measured noise floor at or below −60 dBFS during pauses. Hitting that number is not only about plug-ins, it starts with the room, mic position, and gain staging. This guide explains what “noise floor” actually is, how to measure it, and practical ways to reduce it without creating artifacts or dulling the narration.

What “noise floor” really measures

• Definition: The level of unwanted sound in your recording when no one is speaking, room tone, fan noise, electrical hiss, street rumble.

• Where to measure: Select a clean pause in the chapter, no breaths or touching the stand.

• How it is reported: Most meters show RMS or LUFS averages. For ACX checks, focus on RMS in dBFS during that pause. A reading at or below −60 dBFS is the target.

Tip, measure several pauses across the chapter. A single quiet spot can be misleading.

The order of operations that works

1. Reduce noise at the source

   • Turn off HVAC or move away from vents.

   • Place the mic off-axis from the mouth by a few degrees to reduce plosives, but keep distance consistent.

   • Use a sturdy stand and shock mount to avoid low-frequency thumps.

   • Record at 24-bit, 44.1 kHz, give yourself headroom, peaks around −10 to −6 dBFS on the loudest words.

2. Control the room

   • Treat first reflection points with soft absorption, duvets and thick blankets can help.

   • Put soft material behind the narrator as well as behind the mic, this reduces flutter echo.

   • Record at the quietest time of day. A consistent schedule often produces consistent noise.

3. Clean editing before any processing

   • Remove handling noises and long gaps.

   • Keep a few seconds of room tone from each session, you will use it to bed edits.

   • Avoid hard gates at this stage, they create chopped silence.

4. Light noise reduction, only if needed

   • If the pause measures above −60 dBFS and is audible, apply broadband reduction gently, 3 to 6 dB is often enough.

   • Prefer spectral repair on isolated clicks, chair creaks, or mouth noises rather than cranking a global denoise.

   • Listen for metallic swirls or lisping. If you hear them, you went too far.

5. Subtle dynamics and leveling

   • Use a slow-acting compressor to catch peaks without pumping.

   • Set a true-peak limiter so peaks stay below −3 dBFS.

   • Aim chapter loudness to sit between −23 and −18 dBFS RMS.

   • Re-check the pause. If your floor rose, revisit the earlier steps rather than stacking more processing.

Quick decision tree

• Floor is −48 to −55 dBFS, clearly audible in pauses

  Improve the room or mic placement first, then 3 to 6 dB of denoise.

• Floor is −58 to −61 dBFS, borderline

  Try a very light denoise or a gentle expander on pauses only.

• Floor is under −62 dBFS, but voice sounds dull

  You may be over-reducing. Roll back denoise, add a small high-shelf EQ to restore brightness if needed.

Safe settings that avoid artifacts

• Broadband NR: Start with 3 dB reduction, keep artifacts threshold conservative, preview on sustained consonants like “s,” “sh,” and “f.”

• Expander for pauses: Ratio 1.3:1 to 1.6:1, threshold just below average speech, moderate release so tails sound natural.

• High-pass filter: Only if you hear rumble, start around 60 to 80 Hz for a typical male voice, a little higher for a typical female voice, do not thin the chest.

• De-esser: Use split-band if available, monitor on small speakers so you do not over-soften clarity.

Matching noise across sessions

Different takes, different days, different floors. To avoid a patchwork:

• Choose a reference chapter with the best tone and noise profile.

• Use your room tone from that day to bed edits in later chapters.

• If day two is noisier, tame it lightly, then apply a subtle EQ match to approach the reference rather than forcing heavy reduction.

What makes noise worse

• Normalising first: It raises noise along with the voice, measure and treat before you push levels.

• Hard gates: They produce zero-noise holes that draw attention, especially under headphones.

• Stacking multiple denoisers: A little once is better than a lot twice.

• Monitoring too loud: You will under-treat noise because you do not notice it. Keep a moderate monitor level and always check on headphones.

Measuring, a simple checklist

• Measure at least three pauses per chapter.

• Note RMS values and the range you see, for example, −62 to −66 dBFS.

• Confirm on headphones that the background sounds natural, no shimmering tails or underwater tones.

• Re-measure after limiting, loudness changes can reveal issues you missed.

File prep that helps keep floors low

• Keep one mic, one distance for the entire book if you can.

• Avoid touchy clothing, zips, jewellery, or squeaky chairs.

• Save a few seconds of room tone from each session into a labelled folder.

• Export per-chapter WAVs, consistent names like BookTitle_Chapter_07.wav.

Troubleshooting examples

• Computer fan audible at −54 dBFS

  Move the tower out of the room, use a long USB cable or remote the screen, the floor often drops 6 to 10 dB.

• Mains hum at 50 Hz and harmonics

  Check cables and power strips, try a different outlet, apply a narrow notch at 50 Hz and gentle notches at 100 and 150 Hz only if needed.

• Street rumble during pauses

  Record during quieter hours, add a cautious high-pass filter, then replace the worst pauses with matching room tone.

Final checklist before export

• Pauses measure ≤ −60 dBFS RMS across the chapter.

• Dialogue sits −23 to −18 dBFS RMS, peaks ≤ −3 dBFS true peak.

• No audible pumping, metallic artifacts, or chopped silence.

• Tone and level match the reference chapter.

• File name, sample rate, and bit depth meet the brief.