Volume surges after compression (audiobook recording)

Hello –

I am trying to master an audiobook recording in Audacity using the compress-dynamics plug in. It’s doing my head in because the effect appears to be giving an artificial volume surge to the ends of sentences and phrases. I have been experimenting with compression ratios of 0.4-0.5 with both the standard and advanced versions of this plug-in. Is this something to do with attack and release times? As a novice at this (though a veteran at narrations of all kinds), I must admit I have no notion of whether changing either or both of these would address the issue.

Any ideas or suggestions?

Which plug-in is that? Is that “Chris Capel’s” compressor?
If so, I would not recommend that effect for audiobooks.

I shall add “audiobook recording” to the topic title, which may draw the attention of people that specialize in this kind of recording.

Hello Steve –

Thank you for the reply.

Yes I think it is. The file name ends in compress.ny or compress-advanced.ny.

If that’s not suitable, what is? I did try Audacity’s own compressor once before, and that surging effect was even worse!

Thanks again,

FYI - The [u]Recommended Audiobook Mastering Process[/u] doesn’t use “regular” compression.

It recommends limiting which is a special kind of fast-compression that’s easier to use and it’s easier to get good results with fewer side-effects.

The Mastering Suite treats your entire chapter or sentence, or however you break up your reading, as one block of voice. If you like to weave and bob around in front of the microphone these corrections won’t fix that. Stop moving around.

You are urged strongly to listen to yourself on sealed against the head headphones while you perform to help correct volume pumping.

You can’t listen to the computer to do this. That sound will almost always be late or have an echo. You have to listen to the USB interface, sound mixer or microphone if it provides that connection.

No, we don’t recommend earbuds for recording. They were available for the photo shoot.


Thank you, DVDDoug. I don’t seem to have the effect, Filter curve, which that page instructs me to use (though I do have Classic Filters…, High Pass Filter, Low Pass Filter, Notch Filter).

However, I Do now have the other effects (RMS Normalize, Limiter, and ACX-Check.)

“Filter Curve” is new in Audacity 2.3.3 (and there will be an improved version in Audacity 2.4.0 next month).
Audacity 2.3.3 is available via the Audacity website: Audacity ® | Download for Windows

Koz. You misunderstood. The mastering process is adding volume surges that weren’t there in the original.

Thanks, Steve. I’m on it.

Mission accomplished! This led to a far more satisfactory result with minimal faffing around. Thanks again, Doug!

Hello again –

After applying the recommended steps of Filter, Normalize, Limiter…

I think I could use a gentle Noise gate. Is there a recommendation on this too?


ACX strongly recommend to NOT use a noise gate.

OK. Thank you.

Chris’s Compressor is only partially developed. It doesn’t like the ends of a performance. For example, it is recommended you add some unimportant sound to the ends of a show so the surging damage doesn’t happen on valuable work. After the compression is completed, cut off the extra sound.

Chris isn’t recommended for audiobooks because it also doesn’t like high background noise and can produce pumping sounds on a theatrical reading.

The compressor is not likely to get fixed because Chris reached end-of-life.

Audacity Audiobook Mastering isn’t the only process for producing ACX compliant chapters. But several readers have used it successfully and there is a caution not to mix different processes. If you do use mastering, use it as published.

We can sometimes recommend settings if you post a 10 second sound test to the forum.


Home readers never pass ACX noise. The -60dB specification means your room background sound has to be 1000 times quieter than your voice. So no refrigerators, air conditioners, computer fans, or traffic sounds. Some affordable home microphones have quiet voice volume and can make their own noise. It can be really difficult to reach all three ACX specifications (Peak, RMS-Loudness, and Noise) at the same time. But sometimes we have tricks to get there.


Hello Koz –

Thank you for these insights. Very helpful.

I have never failed ACX, I’m looking to create the most pleasurable experience for the listener, and the most effortless mastering process for me.

I’ll go ahead and post a sound test to the forum as you suggest.

Thanks again,

The test passes with simple Audiobook Mastering.

Screen Shot 2020-08-16 at 7.43.02 AM.png

As you probably found, the background hiss is pretty stiff and annoying.

I can suppress it with Noise Reduction of the Beast. Drag-select some Room tone at the beginning and Effect > Noise Reduction > Profile, and then select the whole thing and Effect > Noise Reduction: 6, 6, 6 > OK.

Screen Shot 2020-08-16 at 7.43.50 AM.png
But that still wasn’t quite enough and I wondered why.

This is a spectrum analysis of the noise by itself. Higher volume is up and pitch is along the bottom, high pitch to the right. We in California call 3Hz an earthquake. Low pitch rumble.

Screen Shot 2020-08-16 at 7.48.28 AM.png
The mountain on the left may be just about right, but the mountain at 3000 Hz is not. 3000 Hz is the tone associated with fingernails on blackboard and baby screaming on a jet. That’s why your background noise seems so harsh and annoying. Because it is.

This is the first time I’ve ever seen a microphone system do that. Congratulations. You’re a unicorn. The voice is terrific, by the way.

What’s the microphone and how do you have it connected?


Very kind of you to do all that, Koz. The microphone is an Aston Origin. But there are a couple of settings on it which can be adjusted, as shown in the photos. The setup shown is housed on a stand in a ‘Portabooth’.


It’s a side-address microphone. You should be speaking into the side grill just up from the company name. The switch on the left should not be -10dB. -10dB setting is for playing a trumpet loudly or recording an explosion. The switch on the right is a rumble filter and doesn’t make a lot of difference since Mastering is going to do some of that job anyway. Leave it flat.

That’s a full-on, Phantom-Powered XLR microphone. How do you have it connected to the computer? Or are you recording on a computer?


Thank you, Koz. That helps a lot.

I’ve zoomed out with this photo, so you can see the setup. The other end of the MicPort Pro connects via a cable to USB port on my computer.