Volume vs Loudness - LUFS & LKFS for Measuring Loudness for Video

in this episode we'll talk about the difference between volume and loudness now are volume and loudness the same thing the answer is no they're not and let me explain why first with some examples number one if you can remember back to the days when we used to watch tv think before 2010 and when you were watching tv your show was on and the show cut to a commercial and the commercial suddenly seemed a lot louder than the show was and you didn't change the volume on your tv so what happened there that's a difference in loudness and likewise imagine your favorite popular music song and then compare that to another song one song may sound a lot louder than the other even when you don't change the volume on your phone or your headphones or your tv or whatever you're listening on that's also an example of loudness so let's talk this through what is volume first of all volume is what you adjust on your playback device it is on your tv it's on your phone or your computer whatever it is you typically turn a knob or some other type of control and that sends literally more power to your playback device to your speakers to your headphones or whatever it is so it's actually moving more air by sending more power to that speaker that's volume now what's loudness on the other hand well loudness is actually defined by the audio file itself the digital audio file and there are a few characteristics that define overall loudness but the main one is what is called amplitude consider all audio is represented as a waveform there are actually waves that are moving the molecules in the air around you and when it's in an audio file the larger the amplitude of the waves generally the louder it sounds however it's a little bit more nuanced than that if for example we play back this wave that tops out at -6 db and we play another one where it sustains for a longer period of time you tell me which one sounds louder so another part of overall loudness is how long a waveform at a certain amplitude sustains over time if it sustains longer it will generally sound louder now to measure loudness why couldn't we just use a metric that gets an average of the amplitude well that's exactly what db rms is now if you're not familiar with that term db of course stands for decibels rms stands for root mean square it's basically a way to average the overall amplitude of the audio now the problem is that it doesn't work out very well and the reason it doesn't work out here are two examples number one is from a podcast where the hosts are talking constantly the second example is from a drama a short film it's a drama and in dramas they're often silent portions between lines of dialogue just to kind of add emotional weight or whatever the case may be the problem is if you use something like dbrms to measure the loudness to get the average amplitude all of those silent portions in the drama are going to bring that average down so even though the dialogue may be exactly as loud in the drama as it was in the podcast the dbrms reading is going to say that the drama was quieter but to our ears they both sound the same it is an old maximum mind that when you have excluded the impossible whatever remains however improbable must be the truth it is an old maximum mind that when you have excluded the impossible whatever remains however improbable must be the truth so what do we do well it turns out there are newer metrics for measuring perceived loudness the way that humans hear loudness and the first one is something called loudness units k weighted relative to full scale which is an absolute mouthful let's talk about that one a little bit it's often abbreviated lkfs it's defined by the itu which is the international telecommunication union now the european broadcast union took that same definition of an algorithm for measuring overall perceived loudness and they call it instead lufs which may be a term that you've heard l-u-f-s stands for loudness units relative to full-scale people have argued about which is the best term european broadcast union says it luffs is the best term from a scientific naming standpoint whatever the case may be for our purposes they're the same thing lkfs lufs now the question is how does lufs measure loudness differently than something like db rms here are a few examples on how they're different first of all it measures integrated loudness that is it measures the entire program so if we're talking about a video it measures the audio from the very start of the video all the way to the very end of the video not just some portion in the middle secondly it takes into account the really quiet portions so for example in the drama those silent portions in between lines of dialogue if anything falls below minus 70 lufs it actually takes that out of the calculation so that it doesn't skew the overall number and what that means in practical terms with the example we used before the podcast and the drama actually measure the same because the dialogue sounds the same loudness in both of them the silent portions in the drama didn't skew the number additionally l ufs applies what's called a k weighting to more carefully represent the way that we as humans hear we're not going to get into the details on that but that's another thing that it does there are also a whole bunch of maths if you want to dig into the math i'll put a link down below for the itu specification for lkfs you can read through it all and you can do your maths now let's bring this back to reality for us for television broadcast there are requirements for the broadcasters on how loud their program needs to be how loud their audio needs to be for example in the european broadcast union european union audio needs to be at -23 l ufs that's the target in the united states it needs to be -24 lkfs that's the target they can't go over that if they go over that they could be fined and the purpose of that of course is to help provide a better experience for those of us that are watching television now when it comes to streaming services online which is where most of us watch our shows these days there are no requirements so there is no specified target imposed by governments what that means in practical terms is that the streaming platforms each define their own targets for example spotify their targets -14 l ufs same thing for youtube it's -14 lufs now in practical terms what does youtube do if you upload a video that's louder than -14 lufs it will actually pull the loudness down when it plays it back to your audience if your audio is uploaded and it is quieter than -14 lufs youtube does nothing just lets it be on spotify it basically moves everything to -14 l ufs and again the idea on spotify for example is so that the listening experience is better for those that are listening so they're not going to have to crank their volume up or down each time when a new song comes on now out of curiosity if you ever want to find out how loud a video is in terms of lufs on youtube play the video back right click in the frame of the video choose stats for nerds it will show you an audio offset that is to say it will show you how far off the audio in that video is in terms of loudness from the target of -14 lufs so for example if it says -6 that means that that video's audio sits at -20 l-u-f-s it's l ufs quieter than the target of minus 14. now here's where i'm going to share an opinion this is purely opinion it is also a recommendation from a variety of people in the podcast world and other people in the audio world as well my recommendation actually when you're uploading a youtube video is to target -16 or -17 lufs now why not the target of -14 that youtube has established in my opinion -14 is a very good target for popular music it makes sense it's loud plenty loud and it's just a good place to be able to normalize all of the audio so that you're not cranking your volume up and down that amount of compression is pretty standard for popular music anyway so it won't drastically change the quality of the audio that you're getting from all of the popular music that's been mastered out of the studios now on the other hand when you're talking about talking head videos or any sort of content that is primarily spoken word that's where i feel like the target really should be minus 16 or minus 17 lufs and the reason i say that is that it retains a little bit more dynamic range so it doesn't sound quite so crunchy if you push dialog audio to minus 14 l ufs in my opinion in most cases it starts to sound really compressed and it isn't necessarily something that's really pleasant to listen to especially if you're listening to something for a long period of time like an audio book a podcast or even a talking head video so for me i typically recommend -16 or minus 17 l ufs now how do you do that let's cover that in an upcoming video get yourself subscribed if you're not already and we'll get you more great videos on how to improve your lighting and sound for video talk to you soon [Music] you

Channel: Curtis Judd

Views: 22,543

Keywords: Audio, sound, video, volume, loudness, LUFS, LKFS, loud, quiet, measure, measuring

Id: nOzZKEWJ5wk

Length: 10min 5sec (605 seconds)

Published: Sun Jan 03 2021