Having a little trouble wrapping my head around something very simple. With the noise gate plugin: I get the Gate Threshold idea. If I set it to -48 dB, anything below that level does not come through. But when it comes to level reduction… why is this also set to a negative? Say I want to get any noise that is -48 dB or lower to zero. You’d think that you would add a positive 48 to get that to zero…
I can tell this is a simple newbie thing. Trying to wrap my head around it. Anybody who can get me to that a-ha moment will be my friend for life.
When dealing with signal levels, 0 dB is “full scale” (+1 to -1 on an Audacity track).
All “normal / valid” sounds therefore have an amplitude less than 0 dB, that is, a negative value.
“Absolute silence” is “minus infinity” dB.
The idea of a noise gate is to reduce the level of the noise - that is, make the amplitude less - that is, make the amplitude in dB more negative.
It seems funny because it is. The job of the gate is not to reduce the noise to Zero. It’s to reduce the noise to -96dB or whatever the most silent value is in the digital system you’re using. This makes the gated sound inaudible.
Zero, or 0dB is the loudest it gets before the system runs out of numbers and starts damaging the show. So those are the two extremes of a common digital system, 16-bit. Both well-known digital sound systems, Audio CD (44100, 16-bit, Stereo) and Digital Television (48000, 16-bit, Stereo) use 16-bit.
That’s not the only way to go. You can use 24-bit which many professional music production systems do and 32-floating which is what Audacity uses internally. But those are not digital audio systems normally found at home. Audacity default is to convert whatever it was doing into 16-bit for Export.
Thanks for these replies. If I read it right, 0 dB is not silence. -96 dB is for all intents and purposes. (- infinity pure silence in principle)
My audio projects (pretty basic) involve a project rate of 44100 Hz and usually two types of files. CD-quality music in short clips in WAVs or MP3s on the one hand, and Skype audio recorded by Pamela at 16000 Hz. The Skype audio is what I’ve been using the Noise Gate plug in for.
I guess I have two questions thanks to the replies:
If normal sounds have an amplitude less than 0 dB and a negative value, why does the “full scale” show a positive value also? Why the positive and negative if sound is just a negative amplitude?
When it comes to the noise gate, say you set the gate threshold to -48. If your target is -96 dB for anything below the threshold, when you set the level reduction, should you set that to -48 or to -96 dB? Does it ‘add’ -48 dB to the -48 dB of the threshold? Or is it separate?
When we talk about dB, we’re talking about the sound meters, not the blue waves. The blue waves are in percent because it’s a little easier to edit like that In My Opinion. The default blue waves don’t even show you all the audible sound, only the loudest parts.
The + and - on the blue waves presents the air motion or vibration which is a back and forth motion. The sound meters measure any movement and the direction doesn’t make any difference.
In this video, you can see a tuning fork which is usually going much too fast to see, slowed down so you can see the individual ±±±±±±± motion.
The threshold is set, to take the above example, so when the tuning fork loudness decreases to the threshold (real) value, the sound snaps to -96 instead of continuing to decline gradually.
Of course, in real life the tuning fork is still gradually getting softer and softer, but the digital show suddenly snaps to “The Blackness Of Space” silence.
Since I know we’re just skimming across the top of the real problem, no, you can’t use a Noise Gate to force your vocal performance to appear a lot quieter than it is. ACX AudioBook videos explicitly forbid you using tricks like that to cover up a noisy room while you’re reading because more often than not, it just makes you sound funny and sounding funny is not good in AudioBook Presentations.
