Dynamics Processing

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Dynamics Processing

Postby HarBal » Mon Jan 17, 2011 7:40 pm

Har-Bal dynamics processing is based on the envelope information HB3 obtains during analysis: the time series constructed from peak and average power levels for each 50ms frame it analyses when a track is first opened. Those time series are what you see in the timeline control above the graph in the Har-Bal UI. The green is the average and the yellow is the peak. That same time series is also used to obtain the peak and average histograms in histogram view.

Now if you don't know what a histogram is it is a graph, representing the likelihood (probability) of the x- value (horizontal axis) occurring. In our case the horizontal axis is level in dB and it is binned in 1dB wide bins (hence the city line appearance of the graph). If you take any one of those tall rectangles, look at the dB value below it and the percent value corresponding to its height you interpret it as follows. Let’s say the column I'm looking at is centred on -5 dB and its height is 7%. That is telling you that for 7% of the time the level is between -5.5dB and -4.5dB (the bin is 1dB wide and centred on -5dB). Now, that could be either the peak level or the average level depending on whether you are looking at the green or the yellow trace.

If you happen to move the gain slider you'll note that the histogram marches up and down the horizontal axis by the amount of gain you apply. Now that you know what the histogram is you should see why that should be, because a level that was in the range from -5.5dB to -4.5dB after a 2 dB gain will now be in the range of -5.5 + 2 dB to -4.5 + 2 dB. However, you might be wondering why when you increase the gain the 0dB bin gets taller and taller. Well, if you think about it, the maximum level we can produce is 0dB. If something was in a -3dB bin and we apply a 6dB gain it can't go into the +3dB bin because there isn't one. What actually happens is the limiter cuts in and forces it into the 0dB bin. Thus, the more you push the gain higher the more the topmost bin in the histogram fills up as the values from other bins are forced into it.

This is a very useful thing in mastering because you can immediately see how over-zealous your limiting is. As an example, take any current generation master of popular music and look at the histogram of the peak level and you will almost certainly see a massive 0dB bin and little left in the other bins. That is what over-limiting does to the dynamics of your track. it squashes them into oblivion.

Back to dynamics processing. Well, the dynamics processing in Har-Bal is based entirely on the average level envelope that you see in the time-line. You create a transfer function to map the input average level to a new output average level and Har-Bal uses it to figure out what gain to apply dynamically prior to the limiter at any point in time. Unlike conventional dynamics processing, it doesn't use attack - decay envelope extraction. The envelope it already has from the analysis. As such the gain change that tracks the music is in sync and symmetrical about the content. By that I mean with normal, a normal compressor you would typically have a fast attack time and slow release which means that the gain quickly drops at the start of a transient and slow falls at the tail. In Har-Bal the dynamics processing is effectively equal attack and release.

Now you'll probably think that makes no sense and will sound awful. In the reality it’s not and here is the reason why. In traditional compression we principally have fast attack and slow release because a compressor cannot predict the future so it doesn't know when to pull down the level and if it does it slowly a very big transient will push through before it has a chance to bring it down. We have a slow release time because fast gain change will lead to a lot of distortion. Because Har-Bal knows the entire history of the track we don't need fast attack because we know when to pull the level down. The net result is that the dynamics processing in Har-Bal works more like the volume riding technique of recording engineers gone past where they adjust down the level while the music is being recorded because they know when the loud parts are about to arrive. This type of dynamics processing introduces very little distortion and as such, sounds quite different to what you might be used to expecting. I've heard it described as sounding more like modest limiting than compression.

That's enough of the theory behind it. How do you actually use it. Well, as hinted at before you design an input-output transfer function using the dynamics node editing tool in the histogram view. Why the histogram view? Because the histogram view shows you a summary of the dynamics content and to stick with a theme in Har-Bal, it will show you the effect your dynamics processing has on that histogram.

The process works like this. A transfer characteristic is made up of nodes. You create a node by clicking the dynamics node tool anywhere on the histogram graph. The node displays as two circles connected by lines, one filled and one not. Think of the unfilled one as an 'O' for output. It represents the level you are mapping the input to. The filled circle represents the input level. So a typical compression scheme would work like this. You look at the average level histogram (green trace) and look at the highest level it has (i.e. where the hill comes down to the flat on the right hand side). At that point you put a node with input and output equal. Why, because we want the top of the histogram to stay put and just squash up the bottom (quieter) parts. Its saying map the input level to the output level of,-for arguments sake let’s say it is -8dB.

Now look at the other side of the hill. Where the left hand slope comes down to the flat we want to map that level to a higher level (compressing it) so we press down the left mouse button (that sets the input level) then drag it up to the level we want to map it to and release the mouse button (that is the output level). For example it might be and input of -40dB and an output of -27dB. You'll note that after releasing the mouse Har-Bal gives you an updated histogram showing the effect of the scheme on it and also the updated average track level figure of merit. You'll also note that if you happen to render those changes and re-analyse the result the prediction is pretty accurate.

That is basically all there is to using it. I'm sure it will seem strange at first until you understand the concepts but once you've gotten the hang of it I think you will find it a natural and informative way of dealing with dynamics.

A couple of observations you can make. When compressing the width of the histogram is compressed but that squeezing makes the peak higher. That is because the area under the curve is constant and sums to 100% (i.e. everything). You can think of it as a lump of plasticine you use to model a hill. If you squeeze the sides together all pushes out the top because the volume has to go somewhere. Similarly, if you stretch it, it falls down, which is dynamic range expansion.

Another thing to note is that this processing can be used for more than just compression. Another useful thing to use it for is noise gating. What I would typically do for that application is to provide a split at the end of the track where it fades away and apply dynamics processing to that split to gate the noise. The setting of the nodes is essentially exactly the same as with compression except you now map the input to a lower level on the left hand side to make the noise quieter. If you have additional dynamics processing applied to the overall track the two mappings are combined.

It all makes for a powerful and flexible architecture for managing the dynamic range of your track.

Cheers,


Paavo.
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Re: Dynamics Processing

Postby janpetter » Tue Jan 18, 2011 3:25 am

I hope for a step by step video of this powerfull tool :-)
All the best
Jan
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Re: Dynamics Processing

Postby HarBal » Mon Jan 24, 2011 6:29 am

I had another question relating to histograms.

I am having a hard time understanding the histogram view. I have read over and over your explanation but still can't get it in my head. After reading your post on the forum about the dynamics riding like techqnique, I thought why not just a waveform. I don't understand the purpose of the 7% on the histogram. Can you please explain the benefit? Also why is the green line so long from the left to where it starts building up activity? That confuses me. Can you also explain the bin? I understand the bin as a container like or a certain area. Is the bin the width of the green city like blocks? I am sorry if I am missing something but I would really like to understand!!!


A histogram shows the frequency (as in how often something occurs) of an event. It comes from probability and statistics theory.

For a pure statistics explanation, lets say I have a bag of ping-pong balls with numbers written on them. The numbers are in the range of 1 to 10. Some of the numbers are the same. Lets say you empty them out and you see these numbers. 1,3,4,5,3,3,1,4,6,7,9,9,9,9,10,7.

A histogram showing the frequency of the numbers from 1 through to 10 is constructed by counting how often each number occurs. So in the above case we have,

Number 1,2,3,4,5,6,7,8,9,10
Frequency 2,0,3,2,1,1,2,0,4,1

That is, there are 2 1's, no 2's, 3 3's, 2 4's, 1 5's and so on and so on.

A normalised histogram usually specifies things in percentages so to convert into a percentage we divide by the total number of balls in the set and multiply by 100. The frequency numbers therefore become,

100 * (2 / 16), 100 * (0 / 16), 100 * (3 / 16), ....

because there are 16 balls in the set. That is what a histogram is. You may note that for normalised histograms the sum of all the frequencies is always 100% because that is the set of all balls in the bag.

Now in the context of Har-Bal's histogram, the balls are each of the sample points on the time line (which are spaced at a nominally 50ms interval) and the number on the balls is the average value for the average histogram and the peak value for the peak histogram. The main difference with the above example is that the time line is a real (ie. fractional) number so how do you group them. Well we group them in "bins" of 1dB width. What does that mean? Take a small subset of average values:

-0.3dB, -0.4dB, -0.7dB, -1.6dB, -2.4dB ....

The bins are centred on exact dB values of 0dB,-1dB,-2dB,-3dB .... The boundary from one bin to the next is the mid-point between centres. The top bin 0dB is special because it doesn't have an upper boundary.

0dB bin ,lower boundary -0.5dB
-1dB bin ,lower boundary -1.5dB, upper boundary -0.5dB
-2dB bin ,lower boundary -2.5dB, upper boundary -1.5dB
-3dB bin ,lower boundary -3.5dB, upper boundary -2.5dB
.
.
.

Going back to the sequence of average values, all we do is figure out which bin the number fits into and when we find that bin we add 1 to it because this corresponds to a count of 1 value fitting in that bin. -0.3dB fits in the 0dB bin, so does -0.4dB, -0.7dB fits into the -1dB bin, -1.6dB fits into the -2dB bin, -2.4dB fits into the -2dB bin and so on and so on. After counting all the values in the bins they get normalised by converting to percentages (100 times the bin count / total number of time line samples).

A histogram, like an average spectrum is much more useful for judging the dynamics of a track because it presents it in a static single image summary. Show me a histogram of the time line and I can tell you immediately whether it is high or low dynamic range, what the limits of the dynamic range is, whether it has a bi-modal behaviour, as in loud parts and quiet parts, whether it has been over limited and so on and so on. It is all there to see in the histogram.

If you find it hard to believe just open up a track you know to have high dynamic range and a track you know to have low dynamic range. Compare the histograms. Can you see the difference. The pattern is obvious and immediately revealing.

The histogram also contains within it the total average level within it. If you give me the histogram I can calculate the track average from the data it presents. It makes a great deal of mathematical sense to summarise dynamics with histograms.

cheers,


Paavo.
HarBal
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Re: Dynamics Processing

Postby janpetter » Thu Feb 17, 2011 12:44 pm

Paavo , what does this tell you ?

http://www.screencast.com/t/QxiSDNFO2

I want to understand that peak in the histogram : - )

All the best
Jan
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Re: Dynamics Processing

Postby HarBal » Thu Feb 17, 2011 6:48 pm

Has your track got a long period of silence in it? I suspect it has and this is the origin of the peak. If you have long silences in the track (that are a significant portion of the track length) then you will get peaks in that location.

In most popular music your not likely to see much here, though for classical music it should be pretty common.

cheers,


Paavo.
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Re: Dynamics Processing

Postby alexande » Thu Dec 29, 2011 10:03 pm

I would need to see some sort of video explaining this as Im sure it makes sense to the engineers but to someone that use to regular dynamics processors this histogram is a foreign language . Also how the histogram alterations interact with the limiter gain slider.
Also, is there some dynamics processing happening when The toggle dynamics button is engaged without anything being done with the dynamics cursor in the histogram page?
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Re: Dynamics Processing

Postby ConkyTPB » Fri Dec 30, 2011 4:47 pm

Hello-

Great job on 3.0, and congrats! I bet you're spent after putting into motion the new features. I can't wait to buy this- the dynamics processing looks very exciting, and I can't wait to get my hands on it. You'll be glad to know that the histogram actually makes perfect sense. (But I had to read it three times! :shock: )

Anyway, just wondering: the dynamics, or "volume riding" that's discussed in the manual... Is that actually muti-band compression applied to just the loud frequencies, or is it across the board? I guess I am wondering how the compression relates to the time splits, say like when you tell Har-Bal to select any areas that peak above a chosen threshold. Is there an option to reassign all of those peaks to the threshold you enter automatically? Or is it necessary to adjust each peak by dragging the levels down manually? I guess I'm not sure if you can even use the dynamics/compression feature in this mode. Maybe it will make sense when I have it in front of me, but this is the one thing that I'm dying to know before I purchase it. Thank you!

Conky
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Re: Dynamics Processing

Postby HarBal » Wed Jan 11, 2012 7:56 am

The introduction in the product manual explains the histogram and control nodes in the context of traditional compression.

There's no multiband compression in Har-Bal. I actually think multiband is a bad idea and have no desire of ever treading down that path. The peak taming feature I have planned for future versions will do all that is required to address problems that have typically been assigned to "multiband compression".

cheers,


Paavo.
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Re: Dynamics Processing

Postby alexande » Tue Mar 20, 2012 4:24 pm

The dynamics is only a slightly less foreign language now that there a little more info out on it. So if the limiter gain slider boosts the volume up in the histogram...why do you need the node tools? What do they do that the slider doesnt?
Why do the nodes travel vertically as well as horizontally? What does moving them vertically do that moving them from side to side doesnt?
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Re: Dynamics Processing

Postby HarBal » Tue Mar 27, 2012 8:55 pm

The gain slider does not change the dynamic range except as a side effectof the limiter cutting it. That is why moving the gain slider only moves the histogram but does not change it's shape (limiting excepted). The node tools allow you to change the dynamic range. It is all explained in great detail in the introduction in the manual (http://www.har-bal.com/help/introductio ... processing).

I suspect the problem is you haven't fully understood what a histogram is and what it tells you. If that is the case then slowly go through the explanation of hostograms in the manual (see "More on Understanding Histograms") until you do, and if there's something that confuses you ask a specific question.

Moving nodes vertically has no effect on the dynamics processing. It's simply allowed so that you can position the nodes in a convenient place as far as the presentation of the histogram is concerned. Only the horizontal positions actually encode the dynamics processing. This is also discussed in the manual.

cheers,


Paavo.
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Re: Dynamics Processing

Postby alexande » Thu Mar 29, 2012 1:00 pm

It would be nice if there were a slot or two to add VST plugins. I use Ik Multimedia ARC to correct the response of my speakers. Currently Im using Virtual Audio Cable to run the output from Har Bal into a VST host which I put ARC into, but the latency is a bit high.
Any ways Ive got a bit of a handle on the dynamics thing. I still like what the Slate FGX does for the mix but I use the dynamics in Harbal to smooth things out a little before I process it with the FX. Cant wait for the VST plugin slot. Itll make it perfect. Thanks.
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