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20th May 2015, 17:50 | #1 | Link |
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Join Date: Aug 2002
Posts: 403
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Microphone recording -> range compression
Hello guys. I have been reading the other topics here related to dynamic range compression and automatic level control, specially tebasuna51's amazing experience with this. I just would like to get some more tips if possible for my very specific application.
I have audio files recorded from a microphone that is placed on a fixed location in a room. People talk in the room from different distances to the microphone (like a meeting) and I would like to make them all sound at relatively the same volume. I can only use ffmpeg and whatever tools ffmpeg have so I was playing with the compand's filter. However, I am not exactly sure how the transfer points work. Do they apply a relative gain on their range or is it a fixed gain? Let me explain. If I set -70,-35, I know it will apply a gain of 35dB to -70 samples and make them sound like -35dB. But what about -65? Will it also apply a 35dB gain making it sound like -30 or does it apply a relative gain? So at a 1:2 ratio the -65 would sound like -32.5db? -75,-35,-20,-20 is: -75 | -35 -55 | -25 -45 | -15 -25 | 0 (clipping) -20 | -20 -15 | -15 0 | 0 Or -75,-35,-20,-20 is: -75 | -35 -55 | -27.5 -45 | -22.5 -25 | -12.5 -20 | -20 -15 | -15 0 | 0 I have been playing with compand's points, but I couldn't come up with good values myself. Moreover, do I need to know exactly the volume ranges of each person in the room to make good guesses on transfer points? Or do you think it is possible to come up with a transfer function that works for all my recordings? Thank you! |
21st May 2015, 12:27 | #3 | Link | |
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Join Date: Mar 2006
Posts: 1,049
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Quote:
Code:
compand=0.1|0.1:0.60|0.60:-76/-999|-60/-30|-30/-20|-20/-15|-9.309/-6.0206|0/-3.103:6:%ngain%:-90:0.6 btw i'm not author for this trick |
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21st May 2015, 20:52 | #4 | Link |
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Join Date: Aug 2002
Posts: 403
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Thank you so much for the reply guys. I have been doing my tests as well and I believe I might have found a way out with compand. I haven't figured all the parameters yet (such as what do I use for soft-knee and a sweetspot to decay), but at least I do get a "normalized" audio on the output. This is my current compand filter (note, this is at ffmpeg filter order):
Code:
compand=.1:.2:-90/-900|-72.1/-12.1|-60.1/-12.1|-48.1/-12.1|-36.1/-12.1|-24.1/-12.1|-12/-12:.01:0:-90:.1 Moving forward, I want to try bringing the individual audio sections to -24->-12 range instead (and leave -12->0 untouched) or maybe do a broader range such as 24dB instead of 12dB. I'm also thinking about using 13dB instead of 12.1dB, which I believe may bring an overall better sound quality with a practically imperceivable volume change. |
Tags |
automatic gain control, compand, dynamic range compression, ffmpeg audio, microphone |
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