What exactly is Soft-clipping?
Old 17th December 2005
  #1
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Thread Starter
What exactly is Soft-clipping?

Alright this is basically a 2 part question. 90% of the artists i record are never going to get there music mastered, and with the crazy volumes everybody "Has to have" i realized when i finish a track i'll throw on either T-Racks clipper or use the soft clip on Cubase's built in dynamics plug, and a touch of L2 and i can basically get a very accurate representation of my mix at extremely loud volumes. First question... is soft-clipping actually chopping off the tops of the waves? By my ears its way more transparent then a limiter yet i don't hear much talk about them.

Second question is, i usually do my mixes and without any volume boast on the mix bus they come out really soft. The other day i had to do a really quick mix and basically just mixed as we were tracking. Due to this my faders were way louder then i'd usually mix, i mean i was almost maxing out some faders. As far as i know being ITB it shouldn't matter if i mix soft or loud especially at 24 bits, but when i was done i needed very little volume boast on the mix bus compared to normal and this track ended up being some of my best work. It seemed like without much added gain at the end of the mix the track held up a little bit more. Is this right, should it matter how loud i mix if in the end it's all going to get finished to -8 RMS. Just curious if mixing louder is a known benift or just a fluke thing happened for me.

Please guys don't turn this thread into a loudness war argument. People want their music loud, so i give it to them and it makes me money. For me starting out getting clients is worth more then arguing over how loud things "should be".
Old 17th December 2005
  #2
3 + infractions, forum membership suspended.
 

Soft clipping is where peaks are brought down in level so that they don't cause distortion at the ceiling, they are not allowed to square off as in everyday clipping. Instead the peaks get rounded tops that do not draw attention to themselves through excessive high frequency energy. This is one of the best ways of adding softness to a mix in the digital domain because you can avoid the harshness that ordinary limiters cause when they are squaring off the peaks at the clipping level. Combining soft clipping with a limiter can be a way of getting the loudness you want and at the same time avoid much of the harshness that else would be produced, since you can limited much less in order to get the loudness you want.

I usually don't touch the output volume fader when I mix (I only use it temporarily to find out different things about the mix), I leave it at unity reference gain. I guess I am used to the analog domain where everything sounds the best near the unity gain marking. I don't know if this is the case in the digital domain as well. Just like you and many other mixing engineers you use the mix output volume fader, sometimes it can be a good indicator of how well a mix sits. You mentioned that you were tracking and boosted the faders and then you didn't have to adjust the mix output volume fader and you realised this was good sounding. To me this sounds like two things happened:

- You were applying less effects than you usually do and saved a lot of the signal this way, resulting in a cleaner final result

- You were tracking instruments that together produced balanced frequency energy, meaning the elements covered their own frequency range well (which is a best practise), the tracks were probably also recorded a little less dynamic or the mix included less dynamic instruments.

Especially the latter mentioned thing is important here, because with much less high peaks you get much less distortion in the end after limiting (through less squares at the ceiling and less distortion through better signal-noise ratio), especially in combination with soft clipping and this makes things louder too. I think that's mainly why you experienced a better final result.

Of course you can control loudness only through using the volume faders, in fact you should if you want a loud final result. I will sum it up. When you mix, some of the instruments are dominant, some are not depending on the kind of element they belong to and what instrument you feel you want to be dominant. If dominant instruments like for instance drums are recorded very dynamically, it will produce high peaks, but the actual RMS level might often be quite low. In order to mix this instrument louder than the rest (by ears) to make it dominant you will over compensate due to the high peaks, so that the volume level of the other instruments automatically are brought down. When the other instruments are brought down in level they get a worse signal noise ratio. During a such situation hard limiting on top of that will create an extremely harsh sounding final result since the transients are cut off really hard and the overall signal noise ratio is so bad. In other words, this is a very important aspect of recording..!!

Due to this phenomenon it's very popular to use compressors with soft clipping during the tracking process, especially when tracking drums, because drums are often one of the most dominant elements with very high recorded dynamic range. Some engineers say compressors are the best tools for getting high dynamic range and that's absolutely true even though it is completely against the nature of what a compressor really does. Above I described what happens in practise, now I will describe how the dynamic range can be improved by using compressors with soft clipping properties. When you track instruments that are very different in transient response you will easily loose signal noise ratio if the dynamic instruments take up a lot of dB on the mix and they are dominant on the mix. When you lose signal noise ratio you actually also lose dynamic range. The reason why compressors with soft clipping properties are so good at increasing the dynamic range is because they allow you to control the transient response so well during the tracking process that you are able to mix the song in such a way that you will not get a bad final overall signal noise ratio and the sound is still very natural sounding. This in combination with the correct track volume balance creates the perception of high dynamic range, because when limiting the overall signal noise ratio is still at max level which means you can more easily feel the dynamics in the mix when the mix is loud.

This is probably the best argument for limiting a song hard, in that loud mixes with good signal noise ratio can create the perception of a really clean sounding mix due to the low noise floor! (even though the actual dynamic range is very low)

This is one of the secrets behind good sounding mixes and I'm sure a lot of engineers would not like this to be discussed so much because this is probably one of the best ways of dramatically improving the sound quality of a mix and every professional engineer has his ways of doing this in the most efficient way. But discussing soft clipping in this context makes this secret really exploited!

This is exactly why the digital domain is seen as harsh sounding and why it's so easy to get a better sounding result in the analog domain. If you track to tape you can use the 0 -> +6 dB range for controlling the transient response and in that way you get a material that is much easier to mix with a good final result.

Generally I think the digital domain is a little raped today. Engineers that are used to recording in the analog domain just record, mix tracks with completely wrong volume level settings, pan wrong due to bad converters, apply a lot of effects on top of that with completely wrong wetness and finally they limit the song hard with something like the L2 to make it sound as good as an analog version. The result of that sounds like a song without energy and emotions, simply a dead sounding mix. Working in the digital domain demands an understanding of how to keep a signal clean, because it's just not like in the analog domain where analog clipping is the solution to evertyhing and applying effects on everything and with whatever wetness you like will create the result you want. Applying an effect wrong on a the wrong track can be devastating in the digital domain! It's not uncommon that engineers put reverbs too wet on the drums when the drums are dominant on the mix, because they are used to creating a large enough room simply by controlling the wet ratio on the reverb and/or delay effect.

Luckily there are still mastering engineers out there that can and also want to save digitally destroyed mixes somewhat. The first thing they do is to prepare their best analog recording medium. It's like: "Ok, this mix was a little digitally raped, I have to try saving the life of this one with the help of my analog partners!"
Old 17th December 2005
  #3
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Not sure about mixing louder, but when you mix ITB, you have an overall ceiling of zero - end of. Set your master fader to zero. Do your mix, and make sure the overall peak level doesn't hit the end of the meter and there you go - you can get as close as you like and will avoid any nasties, although lots of ME's like it if you leave them a few db and deliver under 0db. making up/pulling down gain on a master fader in the digital world probably doesn't do you much good, so get the gain structure of the mix right.

What you're on about - "Volume" is kinda a different thing due to the average level within the track - kind of like why an acoustic track mix might be louder than a rock track mix - more average level and not as many transients to take you up to that zero ceiling. Of course compression, EQ ing etc give you the tools to manipulate those dynamics and all contribute towards the average level in a mix. That's why it's not
as easy as pushing up a bunch of faders to be "loud "! Sure you can get more level by clipping, but it usually doesn't sound that good...

After your mix is good, and taking into account that perhaps in MIGHT get mastered, you should probably try to deliver unclipped mixes and then if people want them loud to listen to use whatever louderizer you have on those finished mixes.

my 2p
Old 17th December 2005
  #4
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Thread Starter
Thanks alot for the info guys, just to clear things up though i always leave the master fader at 0 i never touch it. When i mentioned almost maxing out the faders i meant on the actual tracks. It just seemed that this mix had more punch, was fatter and glued together better then normal. Basically it didn't have that digital smallish sorta sound.
Old 17th December 2005
  #5
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T-Racks clipper - I love it! thumbsup
Old 17th December 2005
  #6
3 + infractions, forum membership suspended.
 

Quote:
Originally Posted by DP40oz
Thanks alot for the info guys, just to clear things up though i always leave the master fader at 0 i never touch it. When i mentioned almost maxing out the faders i meant on the actual tracks. It just seemed that this mix had more punch, was fatter and glued together better then normal. Basically it didn't have that digital smallish sorta sound.
That's cool, it sounds like you have taken a step forward...

One thing I have to add is that you can push track faders up above the clipping level if you have a limiter on the track, I don't think there's any difference between boosting like that and setting the threshold level in the limiter. I usually don't do it like that just in case...

An alternative way of getting a soft clipping kind of effect is to use high and low pass filters. This can work pretty good on the kick drum for instance. When you apply the low pass filter the kick drum moves away in Z direction. That can be good sometimes, but sometimes you want it to stay were it is, only make it a little softer. Then you can compensate by applying the hi pass filter until the kick drum is balanced and enough natural sounding. This can also be a good way of cleaning up the low end if you have a bass guitar around the center as well. For instance you can combine soft clipping and pass filters to maximize the signal noise ratio by applying it during tracking. This can make the low end a lot less muddy. When doing this approach it's important to understand what the frequencies that are cut consist of. Use a frequency spectrum analyzer for determining where the most dominant frequencies are, to make sure that you don't kill the important parts of the sound.

Now you have learned some of the keys for creating a beautiful sounding mix. But wait a second, there's more. Have you wondered how you can acheive analog tape feel in the digital domain? I will reveal the secret. There is a plug in pack called PSP MixPack. That includes PSP Mix Saturator, which in my opinion is one of the best plug-ins ever made! When you set up that properly you can acheive tape warmth ITB. Choose the contour2 preset in the PSP Mix Saturator. Set the drive and shape sliders at max, leave warmth at around 50%. After you have used different techniques for maximizing the signal-noise ratio it's time to add some tape saturation to the track. Important is to not overdo this step, so apply it post fader after you have mixed the track. Now turn up the mix output volume until it's pretty loud. Solo the track you are working on and send a little of the signal to the Mix Saturator effect until you notice it has become a little warmer. When you notice that turn off the solo button and gradually adjust tha warmth of the track until it is as warm in the mix also. The reason why you increased the mix volume was to not overdo anything in case you for some reason still would have a very dynamic material you are working with. If you feel that the low end is becoming too muddy when you apply the tape saturation effect you can compensate this by applying a high pass filter after the effect, but be careful so that you don't overdo anything. When you combine all these steps you have come pretty close to analog tape warmth in the digital domain...

I strongly recommend you try this out...!
Old 1st October 2009
  #7
Gear Head
 

Quote:
Originally Posted by RainbowStorm View Post
Soft clipping is where peaks are brought down in level so that they don't cause distortion at the ceiling, they are not allowed to square off as in everyday clipping. Instead the peaks get rounded tops that do not draw attention to themselves through excessive high frequency energy. This is one of the best ways of adding softness to a mix in the digital domain because you can avoid the harshness that ordinary limiters cause when they are squaring off the peaks at the clipping level. Combining soft clipping with a limiter can be a way of getting the loudness you want and at the same time avoid much of the harshness that else would be produced, since you can limited much less in order to get the loudness you want.

I usually don't touch the output volume fader when I mix (I only use it temporarily to find out different things about the mix), I leave it at unity reference gain. I guess I am used to the analog domain where everything sounds the best near the unity gain marking. I don't know if this is the case in the digital domain as well. Just like you and many other mixing engineers you use the mix output volume fader, sometimes it can be a good indicator of how well a mix sits. You mentioned that you were tracking and boosted the faders and then you didn't have to adjust the mix output volume fader and you realised this was good sounding. To me this sounds like two things happened:

- You were applying less effects than you usually do and saved a lot of the signal this way, resulting in a cleaner final result

- You were tracking instruments that together produced balanced frequency energy, meaning the elements covered their own frequency range well (which is a best practise), the tracks were probably also recorded a little less dynamic or the mix included less dynamic instruments.

Especially the latter mentioned thing is important here, because with much less high peaks you get much less distortion in the end after limiting (through less squares at the ceiling and less distortion through better signal-noise ratio), especially in combination with soft clipping and this makes things louder too. I think that's mainly why you experienced a better final result.

Of course you can control loudness only through using the volume faders, in fact you should if you want a loud final result. I will sum it up. When you mix, some of the instruments are dominant, some are not depending on the kind of element they belong to and what instrument you feel you want to be dominant. If dominant instruments like for instance drums are recorded very dynamically, it will produce high peaks, but the actual RMS level might often be quite low. In order to mix this instrument louder than the rest (by ears) to make it dominant you will over compensate due to the high peaks, so that the volume level of the other instruments automatically are brought down. When the other instruments are brought down in level they get a worse signal noise ratio. During a such situation hard limiting on top of that will create an extremely harsh sounding final result since the transients are cut off really hard and the overall signal noise ratio is so bad. In other words, this is a very important aspect of recording..!!

Due to this phenomenon it's very popular to use compressors with soft clipping during the tracking process, especially when tracking drums, because drums are often one of the most dominant elements with very high recorded dynamic range. Some engineers say compressors are the best tools for getting high dynamic range and that's absolutely true even though it is completely against the nature of what a compressor really does. Above I described what happens in practise, now I will describe how the dynamic range can be improved by using compressors with soft clipping properties. When you track instruments that are very different in transient response you will easily loose signal noise ratio if the dynamic instruments take up a lot of dB on the mix and they are dominant on the mix. When you lose signal noise ratio you actually also lose dynamic range. The reason why compressors with soft clipping properties are so good at increasing the dynamic range is because they allow you to control the transient response so well during the tracking process that you are able to mix the song in such a way that you will not get a bad final overall signal noise ratio and the sound is still very natural sounding. This in combination with the correct track volume balance creates the perception of high dynamic range, because when limiting the overall signal noise ratio is still at max level which means you can more easily feel the dynamics in the mix when the mix is loud.

This is probably the best argument for limiting a song hard, in that loud mixes with good signal noise ratio can create the perception of a really clean sounding mix due to the low noise floor! (even though the actual dynamic range is very low)

This is one of the secrets behind good sounding mixes and I'm sure a lot of engineers would not like this to be discussed so much because this is probably one of the best ways of dramatically improving the sound quality of a mix and every professional engineer has his ways of doing this in the most efficient way. But discussing soft clipping in this context makes this secret really exploited!

This is exactly why the digital domain is seen as harsh sounding and why it's so easy to get a better sounding result in the analog domain. If you track to tape you can use the 0 -> +6 dB range for controlling the transient response and in that way you get a material that is much easier to mix with a good final result.

Generally I think the digital domain is a little raped today. Engineers that are used to recording in the analog domain just record, mix tracks with completely wrong volume level settings, pan wrong due to bad converters, apply a lot of effects on top of that with completely wrong wetness and finally they limit the song hard with something like the L2 to make it sound as good as an analog version. The result of that sounds like a song without energy and emotions, simply a dead sounding mix. Working in the digital domain demands an understanding of how to keep a signal clean, because it's just not like in the analog domain where analog clipping is the solution to evertyhing and applying effects on everything and with whatever wetness you like will create the result you want. Applying an effect wrong on a the wrong track can be devastating in the digital domain! It's not uncommon that engineers put reverbs too wet on the drums when the drums are dominant on the mix, because they are used to creating a large enough room simply by controlling the wet ratio on the reverb and/or delay effect.

Luckily there are still mastering engineers out there that can and also want to save digitally destroyed mixes somewhat. The first thing they do is to prepare their best analog recording medium. It's like: "Ok, this mix was a little digitally raped, I have to try saving the life of this one with the help of my analog partners!"
Oh wow... thank you soooo much!!!! I have just started to experiment with softclipping the way you described. It has made a vast improvement on the sound of my tracks. Gives greater volume and clarity without sacrificing too much dynamics.

Best Regards,
Adam Ashleigh
Old 20th November 2009
  #8
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aclarson's Avatar
Wow. Slightly old thread, but I was just so impressed with the info in it that I felt it deserved a bump. More people should read this.
Old 20th November 2009
  #9
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Quote:
Originally Posted by RainbowStorm View Post
Soft clipping is where peaks are brought down in level so that they don't cause distortion at the ceiling, they are not allowed to square off as in everyday clipping. Instead the peaks get rounded tops that do not draw attention to themselves through excessive high frequency energy.
I still dont get this. I though "soft clipping" was "analog" clipping in software. I fail to see the difference between what a limiter does to the peaks compared to a soft clipper in your explanation...

By listening it sounds like soft clipping (mind you, I dont have any analog experience) is chopping the peaks off, while a limiter "forces" the peaks down instead.

Are there analog soft clippers? Whats the difference between this and compressing with a high ratio?


Good thread
Old 20th November 2009
  #10
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aclarson's Avatar
Quote:
Originally Posted by fragletrollet View Post
I still dont get this. I though "soft clipping" was "analog" clipping in software. I fail to see the difference between what a limiter does to the peaks compared to a soft clipper in your explanation...

By listening it sounds like soft clipping (mind you, I dont have any analog experience) is chopping the peaks off, while a limiter "forces" the peaks down instead.

Are there analog soft clippers? Whats the difference between this and compressing with a high ratio?


Good thread
You make an interesting point, the theoretical explaination makes it sound good, but I can't say I fully understand it myself, seems to have to do with some combination of the knee and how the clipping affects harmonic content.

But as far as an analog soft-clipper, that would be called tubes, right?

This wiki article may provide some clarity:

"Soft clipping is a very important aspect of tube sound especially for guitar amplifiers, although a Hi-fi amplifier should not normally ever be driven into clipping. A tube amplifier will reproduce a wave relatively linearly to a point, and as the signal moves beyond the linear range of the tube (into overload), it distorts the signal with a smooth curve instead of a sudden, sharp-edged cutoff (or even ringing and/or lockup) as occurs with transistors.[citation needed] The harmonics added to the signal are of lower energy with soft clipping than hard clipping. However, soft clipping is not exclusive to tubes, it can be simulated in transistor circuits (below the point that real hard clipping would occur); see section "Intentional creation of distortion" below.
Note also that tube circuits often have huge headroom (overload) margins due to the high voltages they run from, so hard clipping is in reality very rare in a tube stage itself.[citation needed] However core saturation in the output transformer may be "designed in" to some guitar amplifiers when driven hard, and/or the tube biasing may be designed so that the tube passes from class AB1 to class AB2 and starts to draw grid current etc. (these effects are perhaps beyond the scope of this article)
Circuit design may also play an important role in the tube sound; tube circuits are often less complex and laid out differently. It is argued that simplicity is usually best, as the length and complexity can change the inductance and capacitance of a circuit. A more complex circuit will have a more complex sonic distortion characteristic. Minimalist DH-SEs for example typically have a dominant very simple harmonic distortion spectrum. Complex modern transistor designs often have low level but extremely complex harmonic distortion spectra.
In recording industry and especially with microphone amplifiers it has been shown that amplifiers are often overloaded by signal transients. There is a major difference in the harmonic distortion components of the amplified signal, with tubes, transistors, and operational amplifiers separating into distinct groups."
Old 20th November 2009
  #11
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Thanks for the answer... Would be nice if someone else also had some more input on this. A solid state design can clip aswell...
Old 20th November 2009
  #12
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You're right, I was just citing an example more than the entirety. Here's how I'm seeing it: the difference between clipping and compression is that clipping is going beyond the linear operating range of the equipment, where as compression is active gain reduction. I would assume soft clipping would be the point where the gain becomes non-linear, up to the point of audible distortion, which would be hard-clipping. In modern solid state devices and in software, this 'range' basically doesn't exist, the moment it becomes non-linear IS hard-clipping. In tube gear or analog tape, this range is likely wider. And the desireable affect of this would be the characteristics that certian hardware exhibits in that soft-clipping range, most likely being freq and input dependant saturation and harmonic content. So it would seem to me that in the case of a soft-clipping plugin, more than just being a compressor, it's also a hardware emulator, which to some extent is freq dependent compression algorithms based on some analysis of the desired hardware 'sound'.

If someone else has something to add, that would be fantastic, I really think I'm probably missing something here. Unfortunately it probably distracts from the discussions of whatever the next big Chinese mic is, or the how-the-modern-music-industry-sucks rants.
Quote
1
Old 20th November 2009
  #13
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Yeah thats what I kindof thought too... that soft-clipping is a software emulation of clipping in (a certain) hardware channel. So I guess pushing a sound into red on an analog board is soft-clipping aswell?

...and the point where it "turns" into distortion (in an analog channel) its "hard clipping"?
Old 20th November 2009
  #14
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I think the idea of soft-clipping in a plug-in is that it simulates the way a signal starts to break up in (primarily) tube amps. If you have ever messed around with a guitar (tube) amp, you'll notice that, as you increase gain, the signal does not go from clean to distorted all at once: it's more like gain at 1 = 100% clean to gain at 10 = 100% dirty. The range in between, though, is continuous. As you increase the gain, the signal not only gets dirtier (breaks up) but also looses dynamic range. The loss of dynamic range even occurs before you start to hear noticeable distortion.

Contrast this to slamming your output fader in your daw. You can go right up to -.01 db without noticing digital clipping, but shortly after crossing 0 db, you immediately start to hear distortion (which isn't as nice sounding as the distortion your tube amp makes when driven hard).

The soft clip function in plug-ins seem emulate this analog style of clipping. Someone else can problably explain much better than I exactly how this works in a compressor circuit (even an emulated one). I just assume that, when you start to hit the comp hard, the signal starts to break up like it would in a tube amp, not your DAW.
Old 20th November 2009
  #15
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Looks like aclarson beet was thinking along the same lines and beat me to it. Exactly what he said.
Old 21st November 2009
  #16
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Quote:
Originally Posted by Aaron Miller View Post
Looks like aclarson beet was thinking along the same lines and beat me to it. Exactly what he said.
"great minds"

I think both were apt, mine was more thoretical, yours was more real-world.

This actually makes me think the soft-clipping plugin is similar to amp sims, just without hard clipping.

Also, wouldn't a distortion compressor have a similar effect i.e. Distressor?

I have experimented with some interesting routing on vocal tracks a few times where I sent the vocal track to an aux bus, and put a gate on the bus with a range set so it opens the gate fully when the singer screams and closes it for quiet singing, with an expand range from a starting-to-get-loud threshold to fully open. This way there's a gradual increase in signal on the parallel bus the louder the singing gets. Then you put a distortion effect of some kind after it, and mix it in with the main track so it seems like the signal gets more saturated the harder you hit it, which gives a desireable 'clipping' effect. I guess this is kind of what simulated soft-clipping is.

I could see also maybe trying an EQ or even mulitband comp between the gate and distortion for even more control of the saturated sound, I'll have to try that, that could be VERY interesting.
Old 21st November 2009
  #17
Gear Head
 

So, in practice....


In order to maximize the potential loudness from a mix,
you would have soft clipping on EVERY track?

Does the soft clipping come before or after the compressor?

What plug in compressors have soft clipping built in?

I know on things like MILAR charles uses analogue channel on every track
(I think, it's been a while). Is this the same thing?



My gut says yes, do it on every track to varying degrees, do it before compression, and use something like ac-1 or mix saturator. I'm interested in others thoughts on this though.
Old 21st November 2009
  #18
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Aaron Miller's Avatar
Quote:
Does the soft clipping come before or after the compressor?
On the plug-ins that I use (Logic), the soft-clip option is just one of the compressor settings; it determines how the compressor reacts. I'm not sure, in this case, if it can be seen as before or after. Your case may be different and it's certainly possible to put clip/distortion plug-ins before or after compression.

One thing I have noticed is that, when you drive a tube or transformer preamp a bit, you get a bit of natural compression (I'm talking about color preamps here, a 10XX would be a good example, and by "natural" I simply mean you're not using a compressor). The same thing applies with a clip/distortion plug-in and tape too. One reason to do this pre-compressor is so you don't have to compress so much. For instance, when I put a color pre on the master bus and drive it just a bit, I can always get away with a little less compression while maintaining the same average volume level (or, choose to hit the compression just a little harder without sounding like it).

On the other hand, one reason to compress first would be to feed your preamp or clip/distortion plug-in a fairly level signal in order to achieve an even level of clipping (i.e., NOT valleys sounding clean while peaks are clipping wildly).

Whatever comes first really depends on what you're trying to achieve.

I wouldn't suggest putting a clipper on everything as a rule. Listen, adjust, listen again and let your ears decide. That said, it does seem that many great, deep, rich sounding records have a subtle and tasteful clip/harmonics/distortion on a LOT of tracks. This may come into play at mastering to some extent.
Old 21st November 2009
  #19
adl
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Thanx so much RainbowStorm for all the info about clippers and also thanx to aclarson for bumping up this thread. thumbsup
Old 21st November 2009
  #20
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A good example of a hardware soft clip would be the DBX 160SL. Comp first into the output stag and limiter last. This unit has peakstop (hard limit) and peakstop plus (soft clipper). Normally I would put a soft clipper after compressor and dead last in the signal chain. Some cool effects can be done by clipping the signal early and then effecting it though. Cool for hip hop and dance music.
Old 25th May 2010
  #21
MXV
Gear Head
 

Hey, guys.

Rather than post my question as a reply here, I posed it as a new thread in the Mastering forum. Just wanted to let anyone who might have followed this thread know, as there was some good advice here.


I'm basically just looking for the smoothest way to reduce peaks without clipping them off outright, and without any of the the delays that compressors usually try to do. And I'd like to be able to control the ratio or output volume while assuring that I have soft transitions.


My full question on the subject is here:

Compression vs limiting: Best way to transparently reduce peaks?


Thanks sincerely to anyone who can assist with this. I've been talking to the guys on the Reaper forums with limited success.

-MXV
Old 25th May 2010
  #22
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Soft clipping is just a certain type of distortion.

Hard clipping completely squares off the signal, beheading part of it. This creates 2 problems:
1. There is sonic information lost. It doesn't become lower in volume, every part of the wave above the threshold is simply lost forever, like multiplying by zero. You lose detail, depth, and, basically, any characteristics of the sound you had previously, as you push the threshold down.
2. As the threshold goes down (or the signal goes up into it) the squaring off creates many harmonics, theoretically up into infinity. Of course in any kind of physical system, analog or digital the amount of harmonics in a square wave is never very big, but harmonics above the 4th or 5th stop being in tune with the rest of the material. This is due to harmonics' linear nature instead of the logarithmic nature of pitch perception. This is not as bad on simple sounds (like a single guitar note) and it can actually sound rather good, since it starts sounding like a square wave. But on complex material (several notes at the same time) or on bass-heavy material (bass notes have more audible harmonics than high notes, since high notes are closer to our 20k hearing limit) the sound gan get really nasty. Since it's completely out of tune with the original material, it sounds like garbled fuzz (or rather exactly like fuzz, because that's what fuzz is, in a way) on top of the original sound, not blending into it and enriching it but harming it.
3. Hard-clipping on a discrete signal (as in digital) creates aliasing, which sounds horrible (unless the volume is lowered, thus defeating its purpose). That's just the nature of it.

Soft-clipping, needs to be said, is not a nicer form of distortion.
It adds the same odd-number-only harmonics, and creates all of them too.
But the volume of these slopes off much quicker than hard-clipping distortion, which means that higher-order harmonics damage the sound a lot less, being quieter. It retains some of the information above the threshold and sounds less "farty" at low frequencies. Soft-clipping does not create aliasing and in single notes can sound very good indeed; in fact, many people use some on their bass or kick sounds to boost their high frequency content, like an exciter. On more than two notes together, however, it creates intermodulation distortion which is out of tune with the rest of the material and sounds wrong most of the time. It's the kind shit power-amps amps create, and you don't want that, because it doesn't sound "warm" or rich, it sounds like foreign garbled sounds in the mix, unrelated to the original ones.

A limiter is not supposed to distort at all. It's supposed to just lower the peaks in volume without changing their shape. But this is almost impossible to do when you get down to RMS levels because you start hurting low frequency content, modulating it with too-fast volume changes.
On transient material, a surge of distortion like clipping boosts the high frequency content for a brief period of time, and thus can sound acceptable or even great on percussive material. This doesn't modulate the low-end, does not create pumping of any kind and does not need to be fine-tuned for attack and release like clean limiters and thus is both easy and almost transparent, the surge of high harmonics compensating for the transient loss. I have found that in the mastering or just the master buss of modern mixes it's more often than not undesirable to clip, soft or hard, unless the material is particularly percussive. The newest generation of high-end limiters like Elephant or Oxford go well into the RMS area, an area which, if clipped, sounds like a frying pan or a farting contest, because the material is too complex and intermodulation distortion gets unacceptable. I tend to suggest using soft-clippers when mixing (on the kicks, snares, and toms for example) and on single-note material like (usually!) basses and guitar solos. If your mix doesn't sound fat before pasting any kind of effect on your mix-buss, you should fatten the different elements before distorting the very complex master output wave, which, hard or soft-clipped, is going to create intermodulation distortion. Then let the mastering engineer do the limiting. Now if the drums in a mix are very clicky and loud you can often soft-clip them before going into the limiter. You should have done that in the mix buss, though. If you do that anyway, stay away from the RMS area!!!!
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Old 25th May 2010
  #23
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Because I'm singling this out, does not mean I don't think there are other bits in this thread that require comment. This just happens to have caught my eye:
Quote:
I guess I am used to the analog domain where everything sounds the best near the unity gain marking. I don't know if this is the case in the digital domain as well.
It's not even necessarily true in the analog domain.

(I suspect the poster already knows this and I merely caught him in a bit of imprecise prose, but just so the newbs don't get confused... )

What sounds best in an analog chain is proper gain staging of the signal all the way through the chain.

That means setting input trim to an optimal level for the path through the channel. You don't set the trim at unity gain; you set it wherever it gives you the properly optimal signal level.

If you're mixing or monitoring via bus assignment, you'll mix with your faders set appropriate to the relative level required for the mix or monitor mix.

(On occasion, some sort of tricky fader moves might make it worth your while to adjust the trim away from optimal gain for that channel, for instance, perhaps turning the trim down, in order to be able to set the channel fader in such a way as to provide a longer fader throw.)

Now, you will likely want to develop your mix with your output bus faders set to unity gain.

And, unless you're lucky enough to have a full meter bridge, you'll be likely to need to set your individual channel trims by using the bus metering: by setting the channel faders to unity and then adjusting each trim, soloed, one at a time, to achieve optimal signal in each channel. (If your board's channel solos send at unity gain, you can skip setting the channel fader at unity for this step, of course.)

Once you've set up optimal gain for that channel, you can go ahead and mix with the channel's output fader, setting it appropriately for the desired aesthetic blend.

Gain staging seems to flummox newbs and tyros. It becomes a lot easier if you have a diagram of your system in mind or on paper.

The individual parts of the typical recording rig are, functionally, pretty easy to understand if you take them one at a time. But once you start combining them (as in an analog mixing board), things get complex, fast.

That's why it's important to understand the fundamentals and the basic logic of combining them.
Old 28th May 2010
  #24
Gear interested
 

Does anyone know where to find particular algorithms for doing soft clipping/compression computationally? Thanks
Old 28th May 2010
  #25
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Old 28th May 2010
  #26
RiF
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Thanx! Cool thread! One of the few where you can actually learn things.
Old 28th May 2010
  #27
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Quote:
Originally Posted by inhahe View Post
Does anyone know where to find particular algorithms for doing soft clipping/compression computationally? Thanks
I would start search at the DSP and Plugin Development forum over at kvraudio.com
Old 3rd June 2010
  #28
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Quote:
Originally Posted by inhahe View Post
Does anyone know where to find particular algorithms for doing soft clipping/compression computationally? Thanks

The basic transfer function for perfectly soft clipping all the way from amplitude 0 to amplitude 1 is y=2*x-x^2 for x>0 and y=2*x+x^2 for x<0.
Old 29th March 2013
  #29
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Quote:
Originally Posted by Brainchild View Post
The basic transfer function for perfectly soft clipping all the way from amplitude 0 to amplitude 1 is y=2*x-x^2 for x>0 and y=2*x+x^2 for x<0.
</thread>
Old 29th March 2013
  #30
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Quote:
Originally Posted by Thrust View Post
</thread>
hmm, bumping a 3 yr old thread to say the thread is over

soft clipping can be done with a quadratic function as above, or many other functions. the transfer function above also has no threshold, the knee goes all the way to the floor. which can be fine.

overdriven tubes are close to a quadratic function, but have an almost perfectly linear region too, so should perhaps be modelled with a threshold: linear below, quadratic above.

interesting paper on different effects using different transfer functions here

dafx12.york.ac.uk/papers/dafx12_submission_45.pdf
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