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Guided workflow variation

Every chapter checked against ACX,and the fixable ones fixed.

Narrators and producers upload chapter by chapter, and each file has to clear the same audiobook rules. WavSpec measures RMS, sample peak, noise floor, and head and tail room tone for the whole book, then corrects what it can and encodes 192 kbps MP3.

Load every chapter, pick ACX audiobook (Audible), and run one pass: levels, peaks, room tone and MP3 encoding are handled, and the report lists each file.

Pay once. Own it forever.

One-time purchase on the Microsoft Store · No subscription · Instant install

Get it from Microsoft

Buy through the Microsoft Store—instant install, automatic updates, and a Microsoft receipt for easy expensing. No account needed on our site, and no subscription on Store purchases.

Full WavSpec overview
One-time purchase No telemetry Local-first

windows · re-measured from disk · originals never overwritten · nothing uploads

If this sounds like your week

ACX rejects chapters for numbers you cannot hear.

An audiobook goes to ACX as dozens of chapter files, and each one must sit between -23 and -18 dB RMS, peak no higher than -3 dB, keep its noise floor at or below -60 dB RMS, and open and close with one to five seconds of room tone. A narrator checking this with a meter checks every chapter again whenever an edit changes one.

Where tooling usually breaks

One retake can undo a chapter you already passed.

Fix a flubbed line and the chapter’s RMS shifts. Trim a breath and the tail drops under a second. Paste in silence to cover a gap and quality control hears dead air instead of the room. Then the export settings have to come out right again: 44.1 kHz, constant bit rate, 192 kbps or higher, and every file mono or every file stereo.

Where WavSpec lands

One pass over the whole book, with the fixes made for you.

Choose the ACX audiobook (Audible) preset and press Check and correct batch. WavSpec brings RMS to -20.5 dBFS, limits sample peaks, resamples to 44.1 kHz, pads short heads and tails with the chapter’s own room tone, trims long ones, replaces digital silence, renames files that use other characters, and writes 192 kbps CBR MP3.

Pay once. Own it forever.

One-time purchase on the Microsoft Store · No subscription · Instant install

Get it from Microsoft

Buy through the Microsoft Store—instant install, automatic updates, and a Microsoft receipt for easy expensing. No account needed on our site, and no subscription on Store purchases.

Learn more about WavSpec

windows · re-measured from disk · originals never overwritten · nothing uploads

What you get

Feature highlights

Named client specs

ten built-in presets for broadcast, podcast, ad and audiobook delivery, each cited to its source document, plus your own specs, exported and imported as files to share.

Measured per ITU-R BS.1770-5

integrated, short-term and momentary loudness, loudness range, and 4× oversampled true peak, checked against the EBU Tech 3341 and 3342 test signals, plus RMS, noise floor and room tone.

Corrected in one run

gain to the exact target, look-ahead true-peak limiting only where needed, windowed-sinc resampling, bit depth with TPDF dither, and PCM WAV or constant-bit-rate MP3 delivery.

Re-measured from disk

every delivered file is read back and measured again, with up to three passes to land on target, and files that already meet the spec pass unchanged.

A report to send

PDF, HTML, CSV and JSON with before and after values, a loudness timeline per file, client and project details, and a SHA-256 digest for every delivered file.

Audiobook heads and tails

room tone padded with the file’s own room tone or trimmed, digital silence replaced, plain file names, and 192 kbps CBR MP3 for ACX, with originals never overwritten.

Especially when

  • Check a whole batch against the client’s loudness, true-peak and format spec instead of metering and fixing files one at a time
  • Correct loudness, true peaks, sample rate and bit depth in one run, without the gain change pushing peaks over the ceiling
  • Get audiobook chapters within the ACX rules for RMS, peaks, room tone and MP3 format before the upload
  • Send a report with before and after values and a SHA-256 digest for every file, with the audio kept on the PC and the originals untouched

Who benefits

Real-world scenarios

A narrator finishing a thirty-chapter book

The last retakes are in, and thirty chapter WAVs recorded at 48 kHz need to become ACX-ready MP3s before the date the rights holder set for the upload.

Add the folder, choose ACX audiobook (Audible), and press Check and correct batch. Each chapter is resampled to 44.1 kHz, set inside the RMS window, peak-limited, padded or trimmed at the ends, and encoded as 192 kbps CBR MP3 in the delivery folder, with a report listing every value.

Tails that ran long, heads cut to silence

Several chapters end with six or seven seconds of room tone after the last line, and a few open with digital silence where the editor cut out a click.

WavSpec trims each tail to within the five-second maximum with a 10 ms fade, and replaces the digital silence at the head with the chapter’s own room tone, taken from its quietest 500 ms. The report shows the room tone at start and end for every file.

A producer handing a book to its author

A small production company delivers finished books to authors who upload them, and wants a record that every chapter met the numbers on the day it left.

Fill in Report details with the client and the book’s title as the project, then deliver. The PDF report lists each chapter’s RMS, sample peak, noise floor and room tone before and after, the SHA-256 digest of every MP3, and a consistency line across the book.

Deep dive

How WavSpec reads the ACX numbers, one rule at a time

RMS, not LUFS. ACX states its level as RMS, so the ACX audiobook (Audible) preset switches WavSpec from integrated loudness to whole-file RMS in dBFS and aims at -20.5 dBFS, the middle of the -23 to -18 dB window. The level column in the batch table changes to RMS dBFS, so you always read the number ACX reads.

Sample peak at -3 dB. The ceiling applies to sample peak in dBFS, the way ACX states it. When the gain needed for RMS would push a peak over the ceiling, the look-ahead limiter holds it under, with a 0.5 dB margin for MP3 delivery so the encoded file still clears it.

Noise floor at -60 dB. WavSpec measures the noise floor as the quietest 500 ms window above digital silence and reports it against -60 dB RMS for every chapter, so a noisy room shows up in the table before the upload, not in a rejection email.

Room tone at each end. Room tone is the quiet time before the first and after the last 50 ms window louder than -40 dBFS. ACX asks for one to five seconds. Too little is padded with the chapter’s own quietest 500 ms window, mirrored end to end so there are no joins; too much is trimmed with a 10 ms fade. Digital silence at either end is replaced with room tone, because ACX quality control expects to hear the room. The narration itself is never cut.

Format and files. Delivery is constant-bit-rate MP3 at 192 kbps and 44.1 kHz through the encoder built into Windows. Chapters recorded at 48 kHz are resampled with a windowed-sinc converter first. The batch rule checks that every file is mono or every file is stereo, chapters over 120 minutes are flagged, and file names are checked for US letters and digits, with delivered copies renamed to match.

Checked again after the fix. Every MP3 is read back from disk and measured again, and the After columns in the report are those measurements. The consistency line shows the spread of RMS, peak and noise floor across the book.

Author’s Republic too. The Author’s Republic audiobook preset uses the same level, peak and noise rules, pads the head and tail with true digital silence as that platform asks, and flags files over 119 minutes.

How it is built

Built to change only what the spec needs, and show the numbers.

Verified from disk

Every delivered file is read back and measured again, with up to three passes to land on target. The report’s After columns and SHA-256 digests describe the exact bytes delivered.

Originals never overwritten

Sources are opened read-only. Delivered files go to a separate delivery folder as a temporary file moved into place, and Broadcast Wave bext, iXML and LIST chunks are carried across.

Nothing leaves your PC

No account, no telemetry, no update check and no cloud processing. Measurement and correction run on your PC. One-time purchase in the Microsoft Store.

Head-to-head

How WavSpec compares

Feature WavSpec Meter and editor, chapter by chapter Online audiobook processor
Whole book in one run Yes, every chapter checked and corrected in one batch One chapter at a time Upload each chapter
Room tone from the chapter itself Yes, padded to 1 to 5 s from the chapter’s own quietest 500 ms Copied and pasted by hand Varies by service
Delivered as 192 kbps CBR MP3 Yes, at 44.1 kHz, encoded after correction and measured again Export settings chosen each time Varies by service
Report for every chapter PDF, HTML, CSV and JSON with before and after values Notes you keep yourself Varies by service
Where the narration goes Stays on this PC. Nothing uploads. Stays on this PC Uploaded to the service

FAQ

Straight answers—no glossary dump

What are the ACX audio requirements?

ACX lists them in its audio submission requirements: RMS between -23 and -18 dB, peaks no higher than -3 dB, a noise floor no higher than -60 dB RMS, one to five seconds of room tone at the head and tail, 192 kbps or higher constant-bit-rate MP3 at 44.1 kHz, every file mono or every file stereo, and no file over 120 minutes. WavSpec’s ACX audiobook (Audible) preset checks each of these.

How do I check a whole audiobook against ACX requirements?

Drag the chapter files or the book’s folder into WavSpec, choose ACX audiobook (Audible) under Client specification, and press Check only (F6) to see every chapter marked Pass or Fail, with the reason, without writing anything. Press Check and correct batch (F5) to correct and encode. The report lists RMS, sample peak, noise floor and room tone for each chapter.

How does WavSpec add room tone?

It pads the head or tail with the chapter’s own quietest 500 ms of room tone, mirrored end to end so there are no joins, until that end meets the one-second minimum. The padding comes from the recording itself, so it sounds like the room the narrator recorded in. Tails over five seconds are trimmed with a 10 ms fade, and the narration is never cut.

What happens to my original audio files?

They stay exactly as they were. WavSpec opens originals read-only and writes every delivered file to the delivery folder you choose, first as a temporary file and then moved into place. If the delivery folder is the source folder, the delivered file gets a new name, so the original is never overwritten. Copies renamed for a platform’s file-name rule are new files too, and the source keeps its name.

Does my audio leave the PC, and how do I get WavSpec?

Your audio stays on this PC. WavSpec opens no network connection: there is no account, no telemetry, no update check and no cloud processing, and settings, specs and the log stay in your local app data folder. It runs on Windows 11 version 22H2 or later on an x64 PC. WavSpec is a one-time purchase in the Microsoft Store, and the Store runs a 15-day free trial of the full product.

Related pages

-16 LUFS for every episode, from the pilot to the back catalog. A folder of WAVs in, every file at the target LUFS. -23 LUFS and -1 dBTP, across the whole delivery.

A batch of audio in.
A verified delivery and its report out.

WavSpec checks every file against the client’s spec, corrects loudness, true peak, sample rate and bit depth in one run, re-measures each delivered file from disk, and writes a PDF, HTML, CSV and JSON report. Originals are never overwritten, nothing uploads, and the Microsoft Store runs a 15-day free trial.

Pay once. Own it forever.

One-time purchase on the Microsoft Store · No subscription · Instant install

Get it from Microsoft

Buy through the Microsoft Store—instant install, automatic updates, and a Microsoft receipt for easy expensing. No account needed on our site, and no subscription on Store purchases.

Open full product page

ACX and Audible are trademarks of Audible, Inc. or its affiliates. Apple Podcasts is a trademark of Apple Inc. Spotify is a trademark of Spotify AB. EBU R 128, ATSC A/85 and the other named specifications belong to their publishers. WavSpec is not affiliated with or endorsed by any of them.

Technical specifications

Technical specifications for procurement

Spec Implementation
Data Sovereignty Reads only the files and folders you add, or the watch folder you choose, and opens originals read-only; writes delivered files and reports only to the delivery folder you pick, as a temporary file moved into place; settings, specs and the log stay in your local app data folder on this PC
Telemetry Status None; no account, no telemetry, no update check, and the app opens no network connection
Core Runtime C# on a self-contained .NET 10 runtime with WPF, packaged as MSIX for the Microsoft Store; loudness metering, true-peak detection, resampling and limiting are implemented natively; AIFF is read with NAudio, and MP3, AAC, FLAC and WMA use the Windows Media Foundation codecs
Network Requirements Fully functional offline; WavSpec makes no network connections, and the Microsoft Store handles the trial and purchase
Deployment Compatibility Windows 11 version 22H2 or later, x64, with 4 GB of RAM and about 150 MB of disk; one-time purchase on the Microsoft Store with a 15-day free trial
Inputs WAV, BWF, RF64, AIFF, FLAC, MP3, AAC/M4A and WMA; mono, stereo, 5.1 and 7.1; files, whole folders, or a watch folder
Measurement ITU-R BS.1770-5 integrated loudness, EBU Tech 3341 short-term and momentary loudness, Tech 3342 loudness range, 4× oversampled true peak, sample peak, whole-file RMS, noise floor, and head and tail room tone
Correction Gain to the exact LUFS or RMS target, look-ahead true-peak limiting, windowed-sinc resampling, bit depth and float conversion with TPDF dither, CBR MP3 through the Windows encoder, room-tone padding and trimming, and plain file names on delivered copies
Built-in specs EBU R 128 v5.0, EBU R 128 s1, UK DPP AS-11, ARD/ZDF/ORF TV (2025), ATSC A/85 (2026) full-mix / short-form, Apple Podcasts, Spotify audio ads, ACX audiobook, Author’s Republic audiobook, and generic 48 kHz / 24-bit; user specs export and import as files
Verification Every delivered file is read back from disk and measured again, with up to three passes to land on target
Outputs Corrected PCM WAV or CBR MP3 in a separate delivery folder, with bext, iXML, LIST and cue chunks kept and verified loudness written to bext (EBU Tech 3285 v2)
Report PDF, HTML, CSV and JSON with before and after values per criterion, loudness timelines, a batch consistency line, client and project details, and SHA-256 digests of delivered and source files
Automation Watch folder in the app (Ctrl+W); command line with --spec, --out, --check-only and exit codes for scripts