Peaks are too high for ACX Check

Real newbie here. ACX Check fails because my peaks are too high (-2.50 dB) after running Compressor in Audacity 3.3.3. Stumbling through the manual hasn’t shown me what to do.

Can someone tell me, or at least point me to the appropriate section of the manual?

Apply a Audacity’s (soft) limiter … Limiter - Audacity Manual #
As shown here …

[ BTW Audacity’s native compressor is not suitable for speech ].

We have a pre-baked method of setting Audiobook RMS (Loudness) and Peaks.

Audiobook Mastering Macro.

It guarantees Peak and RMS (loudness). If you recorded in a quiet, echo-free room, that may be all you need.

You do still have to conform with the audiobook chapter length, Room Tone (silences), chapter announcements, etc.

There are some lesser known, magic requirements, too. I must be able to buy your book on Amazon right now. I’m not kidding. You can’t submit both book and audiobook at once.


We can sometimes shortcut a lot of anguish and craziness if you submit a voice test to the forum.

It’s 10 to 12 seconds. You can’t submit a book chapter.

Post back if the forum will not let you post that sound file.


Thank you , Trebor. Worked great.

Is there a compressor that can be added to Audacity that IS suitable for speech?

Any old compressor will do if you can set the release-time to, say, 100ms or less.
[ Audacity’s Native compressor has a minimum release-time of 1000ms, i.e. 1 second :snail:].

The free version of TDR Kotelnikov real-time compressor is avaialble for Mac & PC … TDR Kotelnikov | Tokyo Dawn Records (single band compressor, with presets)

G-Multi is a free* multi-band real-time compressor for Mac & PC …
GVST - GMulti [Bonus: can use the high band to de-ess].

[ * donationware ]

A caution. ACX has a failure called “Overprocessing.” That’s why the audiobook mastering processes were all chosen so you can’t hear them running. If you need a compressor to even out your work, it’s possible your recordings are too “wild” or uncontrolled and fixing that may do a world of good.

If you’re in Windows, it’s pretty common for other software packages to “help you” in the background, and you end up with sound effects fighting each other. That can require a lot of coffee to fix.

Also, anything you do to the first chapter, you need to do to all the chapters in that book. ACX requires your chapters to match. There is no applying effects or corrections only “when needed.”

You’re still invited to post a sample. We can’t give you a neat list of all the things you can do wrong, some more obvious than others.

Post back how it goes.


A limiter is a kind of fast dynamic compression. :wink: The limiter will “push down” the peaks with very little effect on the RMS level and no effect on the noise level.(1) The Audacity compressor is very good!

(1) That assumes no make-up gain. You don’t want make-up gain because you that will re-boost your peaks (and boost everything else) and you want your peaks at -3dB or less (more negative), and presumably you’ve already adjusted the RMS level.

Do you have special circumstances that require a compressor for spoken word performances?

You are cautioned about applying peak limiting such that maximum peak loudness is exactly -3dB. Yes, that’s the ACX specification, but the conversion from an Audacity Production to an MP3 Submission while good, is not exact. It is absolutely possible to produce an MP3 with a peak loudness of -2.8dB which does not pass. The mastering system uses a goal of -3.5dB which makes errors like that much less likely.


I hope this response reaches all of you who have provided advice: Thank you.

I am an actor, not an engineer, and am still getting my head around the concept of negative numbers meaning greater volume.

It turns out my problem was caused by double-processing the track. I’ll spare you the details, but I was applying an equalization, RMS normalization, limited MACRO I copied from one of the first tutorials I encountered, then reapplying most of them. As I said … not an engineer.

I tried to post my most recent (and successful) effort for your observations, but new members are not allowed to post.

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