what's the difference between clipping and limiting?

[Lunahorum]

I thought clipping was when the wave gets chopped and isn't allowed to go higher in amplitude. Isn't that what a limiter does? Or isn't that what a 999:1 compressor does?

[OverCoat]

clipping is the horrible ugly popping sound that occurs when a digital waveform is too loud. Limiting is actually what you think clipping is.

[Fray]

I'd say he's mostly right in describing what physically happens in clipping. The sound you hear (clicks, pops, other assorted nastiness) is the distortion from your waveform getting turned into something closer to a square wave when the peak amplitudes all get lopped off to the same max value.

Fortunately there's a threshold of how many consecutive samples have to get clipped before we can actually hear the distortion (I think it's around 6 samples at 44.1kHz). And that's where the limiter comes in: it detects that the signal has gotten too hot and immediately turns it down, hopefully preserving the shape of the rest of the waveform (at least for the length of the release time). So it sounds a lot better than if you'd just let the signal clip.

AFAIK there's really no difference between a 1:infinity compressor and a limiter.

You also need to be aware of where the clipping is happening, and do your limiting before that. For example, if you're recording an external sound source and it's turned up too load, it will clip at input of your soundcard (the A/D converter specifically). Putting a limiter in your DAW of choice (ex. Cubase) won't do anything to help -- you need to turn the volume down or use a hardware limiter (just turn the damn volume down though). Most recent DAWs use a floating point representation for audio, so usually you don't have to worry about clipping happening within the DAW itself, ex. when going across effects or busses. Never hurts to keep your levels reasonable, though. But when you actually bounce your mix down to a .wav file, clipping will occur if the level ever goes over 0dB, so it can be a good idea to put a limiter on the main bus.

If I understand right, a hard limiter with instant attack and release would have the same effect as clipping. You can distort the signal more by making your release time too short on either a compressor or limiter.

[Lunahorum]

so the attack time is how fast the limiter limits the amplitude, and the release time is long it limits the amplitude after the initial limit?

[zircon]

That's correct. "Limits the amplitude" btw means "applies a reduction in volume to a certain threshold level". So the release time impacts how long that reduction will continue after the initial trigger. Ever watched the news with really loud wind or storm noises, and the reporter will say something and it seems like all the other stuff is cut out? That's compression in action, which is simply a less severe form of limiting. And typically, they use LONG release times so that all the wind noise doesn't come back in just because the reporter was breathing in.

Important thing to note; even with compression and limiting, you CAN encounter distortion. If you 'drive' a compressor/limiter too hard, especially with cheaper/free plugins, you will often get nasty-sounding artifacts and distortion. Sometimes it actually sounds like clipping. So be careful!

[Lunahorum]

it's possible to be distorting during the 15ms attack time before it gets down right?

[zircon]

Yes, it is.

[Lunahorum]

please correct me on everything. Just trying to learn how it works.

edit: blue lines in last drawing are not 0db, they are threshold of limiter. maximum amplitude line not drawn.

[zircon]

You're just about correct, but nearly all limiters are 'brickwall' - they simply do not allow sound past the threshold. In other words, attack is more a characteristic of compressors than limiters, which are sort of pointless without that very fast attack to clamp down on clipping.

[Lunahorum]

So what is the difference between a limiter clipping the signal and the DAWxc clipping the signal?

I tried this out with sine waves to see if I could hear a difference and the limiter is definitely lowering the volume, but not clipping it but only if the release is above 800 or so. I am using mda limiter.

Anyways, I don't understand why the limiter doesn't make it sound distorted. It's flattening the wave above the threshold isn't it? I thought that's what it did, but I saved to mp3 and took a look at my super limited sine wave in audacity and guess what, it's just a smaller sine wave that hasn't been flattened at the tops at all. So I guess I still don't understand limiting.

o wait I think i just figured out what's happening. A limiter is a normalizer but ONLY at certain spots. It makes the WHOLE wave bigger/smaller when the threshold is broken. For some reason I thought it only crunched the wave at the top where it went over the threshold, but I guess that's distortion or izotope harmonic adder thing. Ok thanks

[zircon]

The difference is that a limiter DOESN'T clip the signal. It reduces the volume. There's a huge difference. Reducing the volume = makes the waveform smaller in the spot where it normally would clip.

Testing with a sine wave is kind of pointless. Test it with something like a drumloop in your sequencer and you will understand much better.

Don't confuse limiting with normalization... they are really unrelated.. don't even try to make a comparison. Normalization is an OFFLINE process (eg. cannot be done in real time) that analyzes an entire waveforms and increases the volume of it uniformly until the loudest part is just under clipping (0db).

[Fray]

o wait I think i just figured out what's happening. A limiter is a normalizer but ONLY at certain spots. It makes the WHOLE wave bigger/smaller when the threshold is broken. For some reason I thought it only crunched the wave at the top where it went over the threshold, but I guess that's distortion or izotope harmonic adder thing. Ok thanks

Not quite the whole wave, just a portion of it (determined by the length of your release time). I think you understand though.

Thanks for clarifying the attack time bit Zirc, I was thinking to myself the same thing -- that a limiter doesn't make much sense without a nearly instant attack.

[Lunahorum]

"

Don't confuse limiting with normalization... they are really unrelated.. don't even try to make a comparison"

I was comparing them in the sense that they alter the amplitude. My previous understanding of a compress/limiter was that only the part going over the threshold got smaller. Now I know the whole wave changes (from sine wave experiment not turning into a square wave at ultra thresholds)

thx for understanding