I Must Admin, I've REALLY Been Limiting Myself
Yes. I have been limiting myself. Professionally limiting myself. And its really becoming a problem not knowing why. I mean, it started years ago and its only been recently that I could get control of it. I always knew it existed; the limit, and I knew that there were advantages and disadvantages to that limit, but I never knew what that limit was or its real effects.
I'm so ashamed that I never realized the power of knowing my limits.
Oh, no. Not anything that was keeping me from achieving a goal. No. Far from it. The kind of limiting I mean is limiting audio. That's a good thing, but I never really knew why it existed until I watched this Youtube video from a 1944 Army training film on FM versus AM radio.
Radio? What the Flip Wilson are you talking about? I thought you were going to blog on audio engineering?
Ahh, but I am! See, radio and audio are realted. On one hand, audio, concerns itself with what we hear and radio concerns itself with the transmission of what we hear.
Ok. A hard concept to understand, so I'll give you some time to watch the video....
... Right. Too Long, Didn't Watch. Didn't think you would, but nevermind. Its easy enough to understand so I will condense it here.
As we know, audio waves are represented on our screens as a waveform. Mainly as an amplitute (waves that vary in height and depth). AM radio waves work the same way -- The signal vaires in amplitude in order to transmit the voice or music to an AM radio.
But we don't really listen to AM anymore. We're more into FM (assuming we listen to the radio)! And again, what does this have to do with audio and limiting?
I know, I know. But bear with me here. Since you mentioned FM, this is exactly what the point of this blog is all about. No, not the differences between AM and FM radio, but why FM is related to the limiters we use in our audio engineering.
FM, or frequency modulation versus AM, or amplitude modulation has a constant sized wave form, but vaires in frequency. Think an A440 tone being played constantly (No, really. Don't. It will become annoying very quickly). Unless you vary the volume, it will be the same no matter what. Vary the frequency instead and you get the same effect as varying the amplitude, but you might just hear music. In fact, think of FM as...well, music.
Ok, enough of that. So both AM and FM radio suffer when there is some sort of interference and distortion -- either from lightning or in the case of our audio, when we try to record our audio too loud. When that happens, we get clipping. You've heard of that, right. Clipping?
The kind of distortion or clipping we hear in audio is sorta, kinda, in a way related to what happens to radio waves.
So, how can we remedy clipping? Well, lets take a look at FM. When we see something like this above, we can tell the audio is going to be crap. FM radio solves this by... wait for it...wait...for...it...
Limiting (If you'da watched the video, you'd already know that.)
By clipping off the tops where the interference is, we get rid of the issue. But look at the bottom. Still some issue there with how it sounds. We get a harsh tone coming through. Ecccchhhhh.
Why not try smothing it out. We do this with radio waves. Makes it sounds WAY better.
So, to make it sound a bit better, we round off the tops. Well, that's what an FM receiver does.
But what about audio. Dude, that's radio. You were going to say something about audio instead?
Right! So lets take the same principal by looking at this waveform.
See someything wrong? Well you should. If you don't, make a call to the optometrist. I suggest Viewpoint Optometry out on Johnson Rd. in... Nevermind. I digress. You see that the loudest portions are WAY over 0dB (I hope you know what dB is and I hope you know that 0dB is the maximum loudness you can get). That is not going to float. You're going to get clipping and distortion. Did I mention distortion above? No? Read it again.
Anyhow, clipping and distortion will happen here. We could bring the volume down to an acceptable level, but we also sacrifice the target RMS or Root Mean Square -- in our case -17.75dB (Don't judge me. Its my damn example. Go get your own). What if I want to keep -17.75 dB? Lowering the volume won't work. Hmmmm, what to do, what to do?
I know, lets use a technique we learned from FM radio! to remove the possiblity of distortion and clipping. In the FM world, we slightly sacrifice a bit of the sound to ensure there is no distortion (static) by clipping off the tops in a consistent way. In our case, we'll chop off the tops on our waveform to drop the areas that might clip and cause distortion without sacrificing the overall percieved sound.
Here's how it looks once we chop off the tops to an acceptable top end and still keep our RMS about the same:
See what happened when we did a limit. Our top end dB is now -2.51 dB with no clipping AND we kept our RMS roughly the same. Basically no loss of quality because we also employ a bit of rounding off the tops. You might not be able to see it here, but its there. Your DAW should allow you to accomplish this with attack and release.
Now, you can comment and argue "Well, I can do the same thing with a compressor, so limiting is not going to work for me." Cool. What works for you, works for you. What I've found in compressors is that you have to test what the effect the compressor is going to have on the signal after the peak. Is it going to continue to compress long after it should? Is it going to stop compressing too soon? What if it compresses areas I don't want compressed? Not to mention that "infinite" or "flat" compression is guess what? Limiting.
All these are exactly the reason I use Limiter. Lenny B mentioned this Youtube video: "How To Make Your Voice-Overs Louder With Mastering". He argues that a Limiter can work magic when it comes to making your work stand out and I use a limiter to adjust levels for audiobooks.
Anyhow, I wanted to point what limiters were and where they come from and how useful a limiter is. Don't be afraid to learn and use limiters.
Until next time, go make something wonderful.