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Post by robertddl on Sept 2, 2019 8:47:55 GMT -8
It's not a problem, I'm just curious: often, but not always, Audacity shows me a lot of subsonic noise in an audio file. It doesn't seem to be audible, and the high pass filter gets rid of it, but so far I haven't been able to figure out where this comes from, or when it happpens and when it doesn't. In other words, what the hell is this? Is it real, or does Audacity imagine it? Thank you for any theories or information!
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Post by nichalia on Dec 21, 2019 21:52:17 GMT -8
Amazing, right? Those could be room noise, low vibrations from fans or cars, and we don't hear or notice it! This is an interesting paper written about how condenser mics connected to a computer were picking up a lot more of those lower frequencies -- www.ncbi.nlm.nih.gov/pmc/articles/PMC3274121/Human hearing range is about 20 Hz - 20k Hz, but we can still feel lower frequencies. Like when you stand near a subwoofer, and feel the pressure? Those are low frequencies we can't hear. Apparently elephants can hear them, though. Not all headphones and speakers will reproduce them. Things like plosive pops when you say a P or B or T or H right onto the mic without a pop filter? Those are all very low end frequencies, and uncomfortable to listen to. Bumping the mic causes vibrations and that also creates a bunch of low frequencies, which are unpleasant. And there's usually room noise down in the lower frequencies. Doing a high pass filter to reduce them all helps to kill the mic rumble and reduce your overall background noise, which is extra useful if you're working in a home recording space that has some room noise, and you are guilty of sometimes popping the mic, and you still need to record audio that passes certain background noise quietness requirements (like ACX's, for example.) Easy way to cut out a little of the stuff that we don't really need for understandable speech. It's pretty amazing that you've got so much at -5 and lower! Very cool. If we knew any elephants, they could listen and tell us what that is! Or I wonder if it'd be possible to record a bunch of room tone, then pitch shift it way up to listen to what's there?
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Post by robertddl on Jan 12, 2020 0:42:59 GMT -8
Thank you, Nichalia. I've looked at a lot of files - including music I've downloaded from Amazon, CDs I've ripped, vinyl I've ripped, recordings I've made, files from here and there, including output from a voice synth. As you've suggested, I've recorded silence, and pitch shifted it. It hasn't made me any wiser, except that I can rule out pops and bumping as a major factor. Subsonic sounds are everywhere. Amazingly, the highest level was in the voice synth output, so it may not all be actual sound but also some digital artefacts, but it seems that all kinds of microphones may indeed pick up low frequency rumblings way below the 20Hz that their data sheets usually specify - different mics do seem to make a difference. So, we may hear the rumblings of the earth ... or listen in to distant elephant communication ... I'm still surprised that their volume is so high, and that they are not filtered out in professionally produced music.
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