RMS Normalizer adds serious noise after adding to file

Mac Os Sierra, 10.12.6 using Audacity 2.3.3 creating audio in Final Cut Pro 10.4. When I import an .mp3 file into Audacity the file sounds perfect. I select the clip, click on RMS Normalize (a plug-in tool in effects), and the audio is suddenly terrible. There is a distinct crackling/hum. The Limitor does not seem to solve the problem. I record audiobooks for ACX, and need to get this figured out. Why does the RMS Normalize tool cause my audio to deteriorate? BTW - I have used this sequence for other projects and never had this problem. Just started happening today. Thanks for any help!

There’s quite a few puzzled-puppy looks about this.

You can record your voice work in anything you want, but why FCP? Do you already have a studio set up for FCP? I’ve been known to do that.

When I import an .mp3 file into Audacity the file sounds perfect.

Every time you go through MP3, it adds some sound damage and you can’t stop it. Much better to use one of the perfect quality uncompressed formats such as WAV from FCP. Making the 192 quality MP3 should be the very last step before submitting to ACX.

You can save your voice as MP3 in FCP and then go through mastering in Audacity and then make a 192 quality MP3 for submission. The submission is not 192 quality. It’s a combination of the two MP3 compressions. 192 is the minimum quality for submission. If it’s too far off they will bounce you.

There is no mention of Filter Curve > Low Rolloff for Speech in your post. You shouldn’t leave that out. That can get you into trouble. That step takes out all the rumble and earthquake sounds that some home microphones make. Accidental rumble sounds can drive RMS Normalize nuts.

Are you using the audiobook mastering Macro that someone wrote? That Macro is not unconditionally stable and can cause sound problems. Much better to use the three mastering tools manually. Once you do it the first time, the settings stick and you don’t have to write them in each time.

Make sure those exact settings are in the tools when you apply them.

I’m guessing one of two things happened. RMS Normalize settings were wrong or your original clip was more damaged than you think. Did the problem go away when you applied each (and every) tool and carefully checked the settings?


Perhaps you are normalizing too loud, causing it to be distorted.
What level are you normalizing to?

What level are you normalizing to?

That’s two votes for RMS Normalize being set wrong.


Normalization (RMS or regular peak normalization) is simply a linear volume adjustment.

If you are boosting the volume, of course you’ll bring-up the noise floor and you might push the peaks into [u]clipping[/u].

Normally, limiting is used to push the peaks down (a non-linear adjustment) to meet ACX requirements and also to prevent hard-clipping. Extreme limiting (or other dynamic compression) can sound like distortion.