Digital Clipping is a Bad Thing, right? Well in that case why do plugins specifically designed to clip audio exist and why are they popular with people who don’t use them for lo fi effects or sound design? Why Clip?
The consensus seems to be that Clipping is a complementary process to limiting which works well on drums or drum-heavy content.
Limiters go to great lengths to control peaks without introducing distortion. If you change the shape of a waveform it gets distorted, that’s inevitable. The thing limiters try to do is to do this in as transparent a way as possible. One of the main ways to achieve this is to moderate the speed at which this happens, particularly in the release phase of the limiting. This of course affects the sound.
Clippers are popular in applications where the action of a limiter reduces the impact of percussive, transient heavy sounds like drums. In these cases, rather than prioritising transparency of timbre and not introducing any distortion, by using a clipper the peaks can be controlled and on very short transients like those found in drums and an additional edge introduced by distortion can preserve the impact of the drums while limiting their peak value.
But Clipping Is Bad…
For those of us who find the idea of deliberately clipping audio in the digital domain ‘wrong’ (I’ll put my hand up here, I’m one of them), then perhaps considering our response to accidental clips might help. I know that if I’m tracking and a couple of snare hits have clipped I don’t worry about it. On a source like a snare it’s not going to matter as long as its only one or two. On a piano I wouldn’t have the same response. It depends on what is being clipped and this is apparent from the prevalence of clippers being used on drums and drum heavy mixes.
Back in the 90s people were deliberately clipping DAT machines to gain this effect and while this sounds like digital hooliganism it goes to show that for as long as people have been able to clip things digitally, they have been.
While aggressive clipping can be very audible indeed, many people use multiple stages of dynamic range control, each with a light touch and clipping is often one of those stages. But how can clipping make processing more transparent? The idea is that by using a clipper to control the highest peaks you can get more consistent results from a limiter used downstream of the clipper, reducing any audible effects caused by an errant peak pulling the limiter on the material which sits around those peaks in a mix.
What Does A Clipper Do?
Clippers ‘chop off’ the tops of peaks, allowing material to be louder and in a way that is perceived as preserving the transients. This sounds confusing because clipping clearly removes the transients. However, because they do so in a way which introduces audible distortion to the peak, when used on drums the impact of the level of the peak which gets lost through clipping is replaced to some extent by the additional harmonic contend added by the (very short duration) distortion.
The Sound Of Clippers
Just because they all do the same thing, it doesn’t follow that they all sound the same. Raw digital clipping is only one of the ways most clippers clip. Most clippers offer a choice between hard and soft clipping. This controls the sharpness of the corners introduced to the waveform by the clipping ‘chopping off’ the top of the peak and therefore the precise content of the distortion being created. This can vary from subtle harmonic distortion to harsh trash and anywhere in-between.
Oversampling
The role of oversampling has to be considered too. Digital distortion is vulnerable to aliasing, a process by which the Nyquist frequency inherent to the sampling process can introduce inharmonic frequencies which aren’t musically related to the audio. Oversampling is a solution to this problem and is recommended when using clipping unless a potentially harsh sound is desired.
Aliasing and the use of oversampling is a technical area which is well worth getting a thorough understanding of. The best explainer we’ve seen is the video below in which Dan Worrall demonstrates both the problem and the solution, go to 8.30 for the section on oversampling if you’re in a hurry but I recommend you watch it all.
So What Difference Does Clipping Make?
In the example below I have raised the level of some relatively soft sounding solo drums by 12dB using FabFilter’s Pro-L at its default setting and also using Kazrog’s free KClip Zero Clipper in Hard Clip mode. The example plays 4 bars of limiting, followed by 4 bars of clipping and then repeats agains with 4 bars each once more.
While the processing isn’t extreme, the clipped version sounds punchier than the slightly softer limited version with a noticeable change of timbre in the snare. If we look at the two analyses below you can just about see a harder edge to the transients, look for a faint vertical line just behind the leading edge of the hits. Image compression for uploading to the site has softened them a little but if you know where to look they are still visible.
In the video below I have created a test sound from a sine wave which illustrates the effect of a clipper very clearly. Because a sine wave has no harmonics the additional frequencies introduced by the clipper are clear to hear and see. I’ve given this sound a soft attack and even with this un-punchy sound, the way the distortion added to the peak adds a very obvious timbral change is clear, making the sound appear to have more of a transient than it actually does.
How Do Professionals Use Clippers?
We asked friends of the blog for their opinions on use of clippers. Firstly here is a comment from Shane McFee, the man behind Kazrog’s free KClip Zero Clipper:
Shane McFee
“in its simplest form (pure hard clipping, the default in KClip), a clipper just shaves off the peaks of the audio at the threshold, leaving the rest of the audio untouched. Engineers have found this useful for shaving off the peaks of transients while retaining the dynamics of the rest of the material (in contrast to limiters, which audibly "pump" and have a noticeable, and often annoying, effect on the entire dynamic range.)
KClip also offers variable soft clipping, as well as additional clipping curve types, so it can be both a clipper AND a saturator if you want it to be. In that use case, it's both shaving off peaks AND adding harmonics to the signal below the peaks in a smooth fashion up to the threshold.
A typical use case of a clipper can be to shave off extreme transients prior to limiting a master. However, I've also seen clip->limit->clip or limit->clip as signal chains on master buses.
Additional side note: With so many clippers out there offering hard clipping as a default state, what makes them sound different/better/worse from each other? Oversampling. Not just the number of times oversampling, but also the implementation of the oversampling filter itself. One thing I definitely do NOT recommend is clipping anything WITHOUT oversampling, unless you deliberately want aliasing noise as a glitch/effect for some artistic reason.”
Eli Krantzberg has been using a clipper on his drum recordings for some time, he explains his approach:
Eli Krantzberg
“When it comes to drum processing, I'm a big fan of multiple stages of compression (limiting, saturation, etc) where no one single stage is working too hard. I have a bus compressor, EQ, and then K Clip on the bus all my drum tracks arrive at. None of them (Townhouse Bus Comp, Amek EQ, Kazrog KClip) is working particularly hard. I find the KClip adds a bit of thickness overall in a way that helps me not have to be too aggressive on my parallel processing drum bus. It seems to help the individual drum tracks blend together better. I then have my drum bus and parallel processing drum bus arriving at a master drum subgroup, where I occasionally add some more limiting (usually a McDSP ML1). But no single stage is working too hard - that's the key, IMHO, for a transparent sound. The KClip just adds a little bit extra thickness at that first stage of "gluing" the drums together.”
Eli isn’t alone, here are thoughts from three respected mixers who all like the effect a clipper can bring to a mix:
Rik Simpson
“Yes, I use clippers all the time all the time, on anything that wants to be louder in the mix but sounds a bit too pokey when you just turn it up.
I use it mainly on vocals, drums, bass, synths and mix bus (a clipper before a limiter means you don’t need to limit as hard to achieve the same LUFS, it ironically sounds less distorted).
As long as you don’t go overboard with the processing it can make a huge difference.”
Dave Fore
“I usually do because I am working on Hip Hop 95% of the time and it’s become part of my sonic signature. I really like Voxengo OVC-128 and KClip but have just bought GoldClip and it’s fantastic.”
Trond Nedberg
“I use StandardClip in almost every mix I do.
On mixes that need really heavy kick drums, I use it on the kick or the drum bus. It helps me use the 2-bus compressors more for colour without the kick interfering as much.
It is also a nice way to tame unruly transients without the artefacts from a limiter.”
So if you haven’t tried a clipper you might find it useful way to complement your dynamic range control. Although they do a similar job to limiters, clippers usually aren’t employed as an alternative to a limiter, they are used alongside them to make a limiter’s job easier and often bringing some helpful flavour to drums and entire mixes.