How Audio Compression Works

How Audio Compression Works www.garnishschoolofsound.com Hello, it’s Dave Garnish here and we are going to have a very quick look at compression and we’re going to compressively vocal. A compressor reduces the dynamic range of the audio so the quiet bits become larger and the loud bits become quitter and the reason we use compression on the lead vocal is to get more of a consistent level of the lead vocal throughout the song so we can hear the lyrics of the quieter bits and the louder bits on just screeching at us okay. So we’re just going to look at it’s little section of the verse just down here so I’m going to play it for you, alright here it and we’re just going to play them. Okay so here it is. Right, so now so stop it now so we have our second type. Platinum is the kind of old school logic alogarithm that came with the plugin when it very first came out and then here we have some simulations of circuitry. Right so class AR is focused right red series so these are emulating bits of hardware, class U is simulating a URI VCA Central volts of control amplifier and that simulating like la DVX 160 good for drums, kick drums and that sort of stuff. FDT stands for fuel defect transistor which good for vocals similar to a URI 1176 and things like that. An optical is works weirdly, works on a glowing LED so that the brighter that the LED is glowing the louder the signal is going into the compressor. They have quite a unique character these compressors but they don’t kind of— they’re a bit flaky with their attack and release so okay with vocals but maybe not with drums. So for this vocal we’re going to use our URI simulator and as we play through the verse so ready you can see that the compressor is reducing here. Right, okay so now we’re going take it through some of the other parameters. First of all we had a threshold probably just about the most important parameter on the compressor and the threshold basically tells a compressor at which point you want the compressor to start to reduce the gain of the signal so if I play the track and I have the threshold like that it’s not going to compress. It’s probably signal is going to be okay and we see that’s there’s no gain reduction happening here. As we pull it down you can here that the vocal is quieter and it’s reducing because it’s reducing the gain quite a lot yeah, yeah, so we’re going to just move that and then just go now. The next parameter is the ratio and that’s down here at the moment it’s that 1.5 to 1 and basically what that means is if for every 1.5 decibels that exceed the go past the threshold you’ll be able to hear 1 decibel. So if I turn it up to about 8 decibel sorry 8 to 1 then for every 8.7 decibels exceed the threshold you’re only going to be able to hear 1 decibel so that’s compressing quite a lot and you really want to do that with the lead vocal. So we’re going to take it down to about 3 something like that 3.1 so now for every 3.1 DB that goes over the threshold we’re going to be able to hear just 1 DB, okay you know which is pretty much an average setting for female vocal. Okay attack now if your attack is really fast and the compressor is going to react to as soon as the signal gets into the compressor if you make the attack quite slow then the compressor isn’t going to react, the compressor is only going to react 158 milliseconds after the signal that exceeds the threshold has gone in if you see what I’m saying. So we haven’t really got a great deal of time in this video to explain all of the parameters really deeply on my mixing and mastering course there is a workshop called dynamics and we spend a whole 4 hours just on compression. There’s a lot to it so we’re just scratching the surface here so I can’t spend very long on each parameter. Okay, the next one is release. Now that tells the compressor how long to take the gain reduction back off after the transient passes through the threshold. So if I just play the track again, now you can see it has take ages to get back, yeah. The gain is reducing and then it’s like it’s used to getting, not even getting back to zero and if I make the release really fast. Yeah you can see it’s pretty down the threshold so you can really compress anything. Yeah, so she stops singing it’s not back to the 0 almost immediately, okay so just turn that up so you can see yeah. You can pretty see that on the gain reduction. So we’re going to use about a 100 millisecond release okay about 30 millisecond attached pretty good, ratio about 3 to 1 is sounding pretty good for this female wear. Only really going to be interested in this section first we’re not going to worry about the chorus just for this tutorial. We’re not going to talk about the limited threshold. We’re not going to talk about the— and we’re not going to talk about these other parameters out here in this video because it just isn’t time. Right, okay, so we’re going to go back to the top and we’re just going to have, we’re going to get our threshold and we’re going to turn it right up so it’s 0 so it’s not going to compress at all and we’re going to play through and as we’re playing I’m preferably happy with my attack and my release and my ratio as I’m going to play the track down I’m just going to grab the threshold and I’m going to shut my eyes because I don’t want to be distracted by the visual display of the game with that. Okay so I’m just going to use my ears rather than my eyes which is something you should do when you’re mixing tracks, okay it’s very tempting just to kind of get distracted and obsessed by what the meters are doing and you get all your spectrum analyzers out for your over your mix and things like that seeing loads DJ’s kind of look at the spectrum analyzes just to actually see what the frequency is doing and they’re more worried about that than what they’re hearing which is wrong. So I’m just going to play through this whole section of the verse and I’m going to shut my eyes and I’m going to pull the threshold down until I’m kind of roughly happy with what the compressor is doing. Okay here we go. Right eyes shut. Okay that’s is sitting a lot better in the mix. It’s not jumping all over the place so much an important thing is icon here that the compressor is working, okay. If you’re making it this house record and you’re side training it off the kick drum then yeah you really want to hear the compressor working but to compress the lead vocal what we want to do is round off those level so I just play through the verse and hopefully. We’ve achieved our goal there I think we have evened out the levels quite nicely. Using the settings on vocals is fine, I mean the ratio is quite low ratio really might want to use a little bit more of the tack and release fairly normal for a vocal, obviously with the threshold is going to be different. Different vocals are going to be at different levels is all about you know using your ears if you can shut your eyes and great but the important thing is use your ears instead of your eyes. If you’re an architect use your eyes instead of your ears but we’re mixing records so it’s very important not to get to carried away with the meters. So yeah I hope you’ve learned something from that. Sorry we’ve just scratched the surfaces a whole lot more to it but yeah I hope you learned something you enjoyed the tutorial and I hope to see you soon. Tata for now.