ANACHOIC

JUST CURIOUS: The ACX test plugin gives me a Noisefloor of -231.3 dbs, (0.000000).
What is this actually saying? I don’t do audiobooks but sometimes run this plugin on my commercial reads : voice only, no music…just for fun.

Could be a hardware/software noise-gate is being applied before the sound gets to Audacity.

What is this actually saying?

That only happens inside Audacity. You can get values like that when you apply Effect > Noise Gate > Dead Silence or Generate > Silence somewhere in the performance. The silly-high number reflects Audacity’s 32-bit floating internal sound standard. The instant you export an actual sound file, WAV for example, the noise floor should snap back to -96dB or so which is the natural noise floor for 16-bit sound. Even that’s a stretch because Audacity adds a tiny dither sound to your exports to keep standards conversion errors from adding up.

It is possible to fake-out ACX-Check. It looks for the quietest stretch in the performance and measures that for Noise Floor. Again, if you Generated “surgically pure” Silence anywhere in the show, that’s the number you will get. The rest of the show can be insanely noisy, but it doesn’t count.

ACX-Check is our attempt to test at home the same thing that ACX/Audible/AudioBooks is going to test when they get your book submission. ACX has their “AudioLab” on-line tester, but it doesn’t test noise.

Home readers never pass noise. It’s hard to describe objectionable background sounds to someone who’s been living with them for years. Right This Second, I’m listening to the clocks, street noises, amplifier hum, and refrigerator. All seem natural to me, but would never pass ACX Check.

Koz

WAV for example, the noise floor should snap back to -96dB or so which is the natural noise floor for 16-bit sound. Even that’s a stretch because Audacity adds a tiny dither sound to your exports to keep standards conversion errors from adding up.

Actually a silent WAV file (without dither) is -infinity dB, which is true (in the digital domain). You can amplify it by 100dB and you still get dead silence. Quantization noise doesn’t exist until there is some non-zero data.

The ACX test plugin gives me a Noisefloor of -231.3 dbs,

16 & 24-bit WAV files can’t go that low… They will “jump” or “step” to zero (minus infinity dB). It’s possible with floating point WAV. For all practical purposes it can be treated as -infinity (dead-digital silence). For example, if you are listening to a file at 100dB SPL (SPL values are normally positive) the noise would be at -131dB SPL. 0dB SPL is approximately the threshold of hearing so you can’t hear negative SPL levels. …Plus you’d have some temporary deafness after listening to 100dB. :smiley:

Those low levels of noise ONLY exists in the digital domain. When you play a silent file the DAC and electronics will add electrical noise and the background acoustic noise is above 0dB almost everywhere. (There are anechoic chambers quieter than 0dB SPL).

Thanks, people.
The ACX plugin was applied to the whole waveform, not just a quiet part. I did apply a little NR to the read using Audacity’s NR. I’m saving the file as 48/24 so I guess this is just ACX’s reaction to a low noisefloor. Either way, none of this is a problem. Thanks again.