RMS= Root Mean Square. It's a complicated formula. It's like an average loudness but not exactly. It's like an average loudness not including the peaks. The peaks are...well...the peaks. Watch your volume meter. for the most part they want the sound to hover around -23 and as high as -18dB. The sound can go lower but no higher than -3dB at it's peaks. These should be clearly marked on the master volume meter. Garageband should be perfectly fine. If you need to you can look for free metering plugins. Try http://www.lsraudio.com/lvlmeter.html , http://www.voxengo.com/product/span/

Span is particularly good. It has both a detailed meter and a spectral analyzer.

Both of the above plugins are free.

kenhall, post: 406098 wrote:
Your submitted files should measure between -23dB and -18dB RMS, with peaks hovering around -3dB. [Hue explained this]

Your noise floor should fall between -60dB and -50dB. [the noise floor is the level of background noise in a signal, or the level of noise introduced by the system... Plug everything in, set gains, and record the silence in your booth. This will give you an idea of your noise floor.]

To make the audiobook levels louder and more-even throughout is vital. Typically, this process is achieved by RMS normalization around -20db, or compression/limiting. Compression should be applied with a fast attack and release, around a ratio of 3:1. [this Compression 101 text may help: [[url=http://[/URL]="ftp://ftp.dbxpro.co…"]"]ftp://ftp.dbxpro.co…]="ftp://ftp.dbxpro.co…"]"]ftp://ftp.dbxpro.co…]

A hard limiter [a type of compressor] may also be used, and audiobooks are EQ’d during this time, to sweeten the sound and make it more pleasing to the ear. Often, muddled low end ["80Hz roll off/high pass filter {HPF}" can sometimes be built in to the mic, audio interface or both] and mid-range is cut [depends on your sound, hardware, and environment] to make the audiobook sound more clear and smooth.

​Questions:

1) Would somebody kindly interpret this for somebody who is new to these concepts
2) I am currently using GarageBand on a MacBook Pro and suspect that I need some beefier software like Logic Pro to meet these requirements [early on, Audacity worked for my VO needs.]
3) Does the mastering process occur after the recording is done and quality checked using software like Audacity, etc.? [Yes, final step.]

Ken,
I hope this helps.
Dale

It seems that audible is looking for pre-mastered files. Limiting and normalization are applied during mastering. Do not limit your file. They want control over how the file is mastered and limiting your files at this point may prevent them from achieving their goals.

Outstanding responses, and in English too. Thanks for translating this new language for me. I look forward to learning more because it is extremely fascinating.

hueseph, post: 406127 wrote: It seems that audible is looking for pre-mastered.... Do not limit your file.

I have not recorded for Audible. However, I found it surprising that they would want the talent to provide a mastered file.
+1 on Hue's advice. Leave them the headroom to work.

My interpretation is that the -3dBFS peaks and -20dBFS or so RMS are intended to be the final levels and no further processing will be done by Audible.com.

bouldersound, post: 406144 wrote: ...intended to be the final levels and no further processing will be done by Audible.com.

Agreed Boulder. I found the info that the Ken posted, and see that they want the files delivered in 192Kbps, MP3 format. So by their explanation, "mastering" is up to the VO talent. It is my standard M.O. to do some of those tweaks, as needed, while editing, and I never considered that as "mastering", just editing the mix.

Apologies for not including the source link duh

Did it again!

Here's the source [="http://www.acx.com/help/rules-for-audiobook-production/200485520"]link[/]="http://www.acx.com/…"]link[/]: [[url=http://="http://www.acx.com/…"]Rules for Audiobook Production[/]="http://www.acx.com/…"]Rules for Audiobook Production[/]

Ken

From that link:

Audiobook.com wrote: Ensure all MP3 files are recorded, edited, and mastered per the Guidelines above (e.g. MP3 mono encoded @ 192 kbps, maximum file size 170MBs [or less than 2 hours], etc.) Mono files are preferred but stereo files are also accepted. All files must contain the same number of channels, i.e. they must be all mono or all stereo. All files must be 44.1kHz.

Yeah. I read that all wrong. My bad.

-20dBFS RMS does seem a little low by music mastering norms so I was a bit confused at first, but that does make sense since it's just voice rather than continuous full spectrum sound.