Lessons

Lesson Info

Audio Key Terms with Q&A

Wave forms visually represent the loudness of a sound loud sounds have tall spikes like the one with the little yellow top on the left hand side soft sounds or short like we see in the middle human speech, which is this example of the way form is bursting. Each syllable is a burst of sound there's always a slight dip in level from one syllable to the next. Although very short music is more continuous with less fluctuation and levels, the sample rate is we've already talked about this a measure of how many digital measurements samples of the audio was made per second and as we've discovered, the sample rate determines the maximum frequency response ah forty eight case sample rate is a perfectly good choice for most video projects. You can do a sample rate of forty for one, but most campers are preset to be forty eight just the way that cd's air preset to be forty four one both of them yield audio, which exceeds the range of human hearing at the high frequencies. Bit up is a measure whic...

h determines the amount of dynamic range in a clip the distance between the loudest and the softest passages ah, sixteen bit depth it's another good choice for most video projects editing at a higher bit ups like twenty four is a perfectly good thing to do for audio mixing but is not necessary for audio recording now audio recording for the census of music creation is a different environment we're talking video and audio audio for video was supposed to audio from music audio editing most of what we've learned about video editing also applies to audio editing we set ins and outs the same way and we edit it down to the timeline the same way this chapter covers techniques which are specific audio final cut ten supports a wide range of audio formats a f broadcast wave cf which is a generally a surround format wave formats which is on compressed a c which is compressed mp three which is an mpeg three compress file an mp for both un compressed on the left and compressed on the right there's a new section of the interface inside final cut that we have not yet talked about called the inspector I'm going to be exploring this mohr and morris we move out of editing and into effects the inspector is the place in final cut where we make changes to whatever has selected its keyboard shortcut his command before the inspector is crucial toe working with audio transitions in all effects it is not necessary at all for importing media editing or trimming by default all projects and final cut create a stereo mics though you can easily change this to surround if you wish you can not change it to monaural all audio settings and effects are applied to the clip though you can use compound clips which we talked about yesterday afternoon to apply and effect to a group of clips but settings effects are clipped based not track or layer based and just to reinforce because I want to have everybody not yell at me later this one is just absolutely crucial. Audio levels must never exceed zero devi during export they will exceed zero during mixing sorry during uh editing but that's because you haven't set your levels but as soon as you exported or lay it off to tape create a file from it your audio is destroyed we don't want that to happen also there's a lot of discussion and jim I know you know this because you spend your life in audio there's a lot of discussion on how audio gets measured there's there's average whips there's average levels there's there's loves levels there's are a mess levels there's peak levels there's v u levels audio is measured inside final cut on the scale called d b f s decibels full scale, which means all of my comments are related to peak levels, which drives most audio engineers nuts because they're used to working with average levels and final cut we're dealing with peak levels, not averages and the numbers that I share with you in terms of setting levels are base on those peak numbers weakened by plug ins that give us love's measurement and l ke a fest measurement and average level measurement, but those levels are a third party plug in there not supported natively by final cut I've mentioned that audio is log rhythmic and this is something that we haven't seen before. First text hiding underneath a graphic and second the graphic itself, which is thie audio levels the audio mees meters, which is what we see on the right measure audio levels zero d b at the very top is the loudest you can get, and the little numbers up above that say nine negative four indicate that the the audio is below zero it's not distorted, they turn red, we're in distortion. The thin yellow line that we see above the green bars is called the peak hold indicator and there's a peak hold indicator for each channel, the left on the left and the right on the right. Audio is measured a negative numbers because whoever invented audio hates people, and they like dealing with negative numbers, which means the larger the number, the soft of the volume. And as I said, for every sixty being level, the audio drops fifty percent, okay, two more things, and I think we're done with the definitions and all the hard, heavy lifting of math class today, there are two types of audio levels inside final cut relative and absolute a relative audio level is displayed. When you're changing the level of a clip, you're changing it relative to the level of which it was recorded. We're making it louder than the level at which it was recorded were making it's softer on the level in which it was recorded. The absolute audio level is displayed on the audio meters the absolute accurate measurement to the volume of the sound, whether you're listening to a single clip or the entire project, if you're new to mixing audio and you're distributing your project on the web, set the levels of your mix so that the audio meters air bouncing between negative three d b and negative six d b broadcast uses different specs. Cable uses different specs theatrical digital uses projection uses different specs, but for the web, having your master levels bounce between negative three and negative six is a really good choice. The l cast meters from meter plugs that meter plugs dot com slash l cast provide measurements that meet the calm act, which means that our audio levels for broadcast have to be essentially the same as commercials and you could get plug in meters to do that. And jim, one of the things that I heard during the chat is, can we have stuff go out to proto? Ls and the answer is yes there's ah program called x to pro from x to pro net, which converts final cut projects into projects which could go to pro tools. We can also export from final cut to go to adobe audition, but in both cases it requires third party utility software great. Thank you lotta folks were asking about that perfect one last thing we talked about reference way forms, and we turned them on by enabling a check box inside the the editing preferences where it says show reference way forms and if you notice the picture on the left, we don't see any ghosted back wave forms, but if we look at the picture on the right, there is some ghosted back audio levels that make it look like your audio was recorded at full volume reference. Way forms show ghosted audio way forms as if the actual wave forms were amplified the maximum amount these could be useful when trying to mark clips containing very low audio levels, and they are turned on and off with a preference, and they have no effect on output. One more thing, key frames this is the last definition. A key frame is how we're gonna animate audio levels. Changing during playback on that key frame is defined as a point of change during playback. If we want something to change during playback, we use key frames were goingto introduce q frame's with audio levels because it's easy to understand, but we're going to use key frames a lot tomorrow when we talk about animation in effect, we always use key frames in pairs there's always a starting position there's always an ending position there's a starting point to the volume in unending point to the volume and we make that change using key frames so that's where we're headed, the last thing I cover is going to be analysis and how you adjust the analysis and more importantly, why you would want to adjust it and when you'd want to move it to other applications. The audio analysis and noise reduction inside final cut is okay and much better than it was in final cut seven because it didn't exist there at all. But there are much better tools out there, and all of them revolve around the fact that everything we hear everything we hear is based on that frequency range of twenty to twenty thousand cycles when we remove noise. Noise is not something separate from human speech but it's all part of the same range of frequencies, so the trick is to remove noise without damaging human speech and that is a whole lot easier to say than to do another question yeah, this is from caleb bail can you touch on bit rate I filmed the wedding last year using a zoom age for for the first time and apparently recorded audio separately on a different bit rate than I needed then when I tried sinking the audio in the video I found the audio was different frame rate bit right determines how many samples per second or recorded and most of the time final cut does a good job of reconciling forty eight well hang on time out bit rate is different from sample right if by bit rate you are actually meaning the level of the speed at which the audio clip was compressed because you were recording it as an mp three file bit right is determining the quality of video or audio compression which determines file size which ultimately determines audio quality hopefully you don't record mp three audio that would be bad you want to record a f or wave audio which is un compressed final cut does not like compressed audio so if you actually recorded mp three audio our mp for audio you need to convert the audio from a compressed form mpeg three or mpeg four into un compressed for the purposes of editing inside final cup so if by bit rate you mean you compress the file you need to run it through a program like apple compressor or emp extreme clip or handbrake or adobe media encoder and convert the audio from whatever it is into a linear pcm or a f or wave file all three words mean un compressed audio you want to convert it to forty eight k forty eight thousand samples per second and a sixteen bit depth which determines dynamic range forty eight k sixteen bit depth if by bit rate, however, you don't mean the fact that it was compressed because compressed audio will cause problems with final cut if by bit rate you actually mean sample right here there's an issue final cut will deal with two different sample rates forty eight k and forty four one standard for video in the standard for audio cd and you could use them interchangeably on the same timeline if on the other hand some low end consumer cameras and low end audio recorders and I used zoom every day but I have to change the menu settings to get it to work you can record a thirty two bit thirty two thousand sample right speed. The problem is this is going to cause your audio and video to drift out of sync if you have files which are compressed mpeg three mpeg four files which are recorded at a sample rate which is very low thirty two or twenty two thousand samples per second it's important that you run it through a compression program and converted to a f or wave which air to un compressed formats forty eight thousand samples per second and a sixteen sixteen bit depth to get the dynamic range you want, once he comes in his un compressed, then final cuts can edit it. And you're not gonna have any sink drift. And you're not gonna have any audio and video out of sync.