Newbie question - Compression and...

Hello. I am recording my two books that are selling well on amazon. I sent a sample to ACX and this is what they responded:

Your audio is currently measuring at about -27dB RMS, which is quieter than the ACX required range of between -23 and -18dB RMS. To remedy this we suggest applying a bit of compression to your audio. Second, your audio is peaking at -0.6dB at its highest point. This is higher than the ACX required -3dB peaks. Try also applying a limiter to your audio with the output ceiling set to -3dB and adjust the threshold settings to get a bit more overall loudness without clipping.

I’ve tried to find out how to do this, without success. How do I apply “a bit of compression”? How do I adjust the peak? And how do I apply a limiter…and threshold settings?

I am fairly computer literate, but far from an expert! Is there someone who can tell me exactly how to do this? Much appreciated.

Cap’n Jon

I think we can do that, but you need to know that when we emphasize the low volumes and suppress the high ones, the room noise level is going to come up. If you’ve been just skating by with the neighbor’s dog and traffic noise in the quiet parts of the show, those are going to get much worse. Most people don’t live in a studio.

Select the whole show (click just above the MUTE button on the left).
Effect > Compressor > OK (use the default settings)
Effect > Amplify: Second Number -3 > OK.

That should make your overall volume louder and denser and still not let your peak sounds go over -3.


You are experiencing the difference between live recording and the stuff you buy. Live Recording tends to be clean and open, natural and clear, but not very loud. Everybody is expecting their purchased performances to be very loud and dense and forward with few if any variations in loudness.

We break it to them that the difference between those two shows is usually thousands of dollars of expensive studio time with a talented audio engineer.

Listen critically to the work after you apply the filters. The finished show will not be perfect (see: thousands of dollars). Post back with anything you don’t like. Note that good speakers or headphones are required for audio production. You can’t do any of this on the speakers in the laptop.


Some plug-ins allow you to set another threshold for the noise floor (e.g. Chris’ Dynamic Compressor, in the new plug-ins section of the Nyquist Forum).
But it might be good to have a analyse tool that gives you comparable results (peak and RMS) for your track. Thus you can see the immediate results. We want to be within the limits without too much manipulations.
I am going to attach Steve’s “Wave Stats” plug-in. Put it into Audacity’s plug-in folder and restart Audacity. It will now be found in the analysis menu.
It takes one parameter, namely the length (in s) to analyse. you might want to enter a real big number.
The RMS value is weighted with a standard curve i.e. filtered and the results may be lower than stated above.
If so, a un-filtered RMS value may have been chosen by the amazon people. But that could easily be adapted.
stats.ny (2.12 KB)

Thank you, gentlemen for your quick responses. I will be going to my little studio later and will record a story and apply what you suggest. My studio is a small room in a quiet, secluded area adequately soundproofed. It’s reassuring to know that there is guidance out there for me! Cheers Jon

Little correction to my previous post:
The maximum size seems to be 30 s for the wave stats plug-in, although higher numbers can be entered.
However, it may suffice for the moment.
Just give it a try and we will see what RMS and a-weighted RMS values it spits out.

Koz - Should I apply those settings before or after I do the noise removal…or does it matter? Thanks, mate!

My studio is a small room in a quiet, secluded area adequately soundproofed.

Should I apply those settings before or after I do the noise removal…or does it matter? Thanks, mate!

If your studio sounds OK, what are you applying Noise Removal for? Noise Removal can create other problems and you probably should not use it if you don’t have to.

I don’t have a ready answer. Try it both ways. Most of the tools carry instructions based on they’re being first to the party. A repair technician had a sign over his bench that if you tried to fix it first, it would cost you double for him to fix it.

And just to be clear, the Studio is of paramount importance – you’re right. I have been known to get huffy about recording an Important Person’s Voice if I could not use a specific, quiet room. “Hi, Rosa? can I beg a schedule change with you…”

Do you have any raw, unprocessed capture posted anywhere we can get to it? I’d like a perfect WAV file if possible. I want it longer than is possible here on the forum.