How to increase noise floor

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dsaudiobooks
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How to increase noise floor

Post by dsaudiobooks » Thu Feb 25, 2021 12:08 pm

I'm kicking myself because I've made a newbie mistake. I'm recording my first audiobook and didn't save a copy of two raw files. In processing, I applied Noise Gate but then forgot to check that the files met ACX requirements. I then saved the files but when I went back to them later and did the ACX check again, they passed except for the noise floor, which was too low at -94.21. The annoying thing is I had used Noise Gate before successfully in test recordings. I am recording to an HP SSD laptop using Windows 10 and Audacity 2.4.2 in a small soundproofed home booth. I use a Rode NT1 mic, through a Shure High Pass filter and Audient iD4 preamp. I use a macro with the following effects: RMS Normalisation, Graphic EQ, Limiter, Noise Gate, De-clicker, De-esser. I know, I thin, how to make sure this doesn't happen again but would like to know if it is possible to increase the noise floor on the two files so that I don't have to record them again.

steve
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Re: How to increase noise floor

Post by steve » Thu Feb 25, 2021 12:18 pm

dsaudiobooks wrote:
Thu Feb 25, 2021 12:08 pm
the noise floor, which was too low at -94.21
That is extremely low.
IF that is the result of excessive noise reduction, then I'd expect the sound quality to be noticeably damaged (bubbly metallic artifacts).
(there could be other causes for extremely low noise floor)

What settings did you use in Noise Reduction?
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dsaudiobooks
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Re: How to increase noise floor

Post by dsaudiobooks » Thu Feb 25, 2021 1:11 pm

I had the Level reduction at -21dB, gate threshold at -31.30dB and the attack/delay at 10ms - I have since changed the level reduction to -5dB, which gave an ACX pass and sounds OK. But that obviously doesn't solve the problem of the two files I have already recorded.

steve
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Re: How to increase noise floor

Post by steve » Thu Feb 25, 2021 1:46 pm

It's best not to use Noise Gate at all for work that is to be submitted to ACX. They specifically say in their instructions "don't use a noise gate".
A little, gentle "Noise Reduction" can be helpful, but you shouldn't be able to hear that the effect has been used.
dsaudiobooks wrote:
Thu Feb 25, 2021 12:08 pm
would like to know if it is possible to increase the noise floor on the two files so that I don't have to record them again.
It would be best to record them again.

You could mix in a bit of noise and achieve the specification figures, but that won't improve the sound, and it is what it sounds like to human listeners that matters most. "Over processing" is one of the most common reasons that ACX reject submissions.
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David Mack
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Re: How to increase noise floor

Post by David Mack » Sat May 08, 2021 2:56 pm

Hello DS,
I think you might be looking at your perceived problem in reverse. Keep in mind the measurements are negative numbers.
That is, -30 decibels is noisier that -60 decibels. All negative numbers go in reverse. So, when the required background sound is meant to be no louder than -60 dB, then -90 dB is in fact quieter. If you have a recording with, say, a noise floor no quieter than -40dB, then it is too loud in terms of underlying background noise, that's why ACX insists on no greater noise than -60dB. So, you had no problem, and certainly would not add noise.
Now, the reason ACX doesn't encourage the use of a noise gate is because when they accept your recordings, they use a noise gate to drop the sounds between words other than a light natural breathing. They also flatten all the levels of different files so they are the same within a few dB.
ACX worries that if the sound gate is used twice - once by you and then again by them - in many cases the background sound would drop to under 120dB, in which case their machinery might conclude there is no recording at all at some point and flip to the next file.
They don't state this clearly as they fear the result would be confused people.

kozikowski
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Re: How to increase noise floor

Post by kozikowski » Sat May 08, 2021 4:30 pm

the reason ACX doesn't encourage the use of a noise gate is because when they accept your recordings, they use a noise gate to drop the sounds between words other than a light natural breathing. They also flatten all the levels of different files so they are the same within a few dB.
And you know all this because.......?

Koz

DVDdoug
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Re: How to increase noise floor

Post by DVDdoug » Sun May 09, 2021 8:00 pm

As far as I know, ACX doesn't do any processing but of course they require your file to meet their loudness and noise standards.
Now, the reason ACX doesn't encourage the use of a noise gate is because...
I assume it's because a noise gate will "hide" the noise in your recording from their automatic test, it makes it harder to measure the true signal-to-noise ratio, and it can sound bad and be distracting (if you can hear the noise gate working).

I've watched some old black & white movies on DVD that were noise-gated. I'm not really noticing the background noise until the noise-gate suddenly kicks-in you get dead-silence. It's distracting when it goes totally silent and for a moment I'm thinking the sound has failed. I haven't tried measuring it but the background noise in these movies (where it's not gated) is much worse than -60dB. Gating from -60dB to -infinity wouldn't be nearly as distracting, if I could hear it at all...

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