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Crest and Dynamic Range Confusion Metering & Analysis Plugins
Old 5th February 2011
  #1
Gear Nut
 

Crest and Dynamic Range Confusion

Hi all,

I seem to be reading conflicting information regarding crest factor and dynamic range. It was my understanding until reading P168 of BK's Mastering Audio that they were one in the same?

According to some other threads the DR is the difference between the loudest and quietest passages and crest factor is the immediate difference between RMS and Peak Levels.

Where my confusion lies is with the TT dynamic range meter. Correct me if i'm wrong but the TT meter shows RMS and Peak levels and the sum of the difference as the DR, after all the meter is constantly changing.

Thanks in advance
Old 5th February 2011
  #2
Gear Head
 
uros's Avatar
 

You are right. DR is the difference between the loudest and quietest passages and crest factor is the difference between average (RMS, VU...) and Peak Levels. You are confused because these two terms are used interchangeably (like phase and polarity).

Hope this helps.
Old 5th February 2011
  #3
Gear Nut
 

Thanks for that.

Can you shine any light on what the TT DR meter is indicating? For example if i play 5 seconds of the loudest part of a song how is it able to give me a DR reading?


Thanks
Old 5th February 2011
  #4
Gear Head
 
uros's Avatar
 

You are welcome. I must admit that I haven't used TT DR meter (despite I downloaded and installed it) but since it was developed with the idea to help fight the loudness war I assume it indicates the crest factor.

Cheers.
Old 1 week ago
  #5
Lives for gear
 

Quote:
Originally Posted by uros View Post
You are right. DR is the difference between the loudest and quietest passages and crest factor is the difference between average (RMS, VU...) and Peak Levels. You are confused because these two terms are used interchangeably (like phase and polarity).

Hope this helps.
Is this really the case? I believed, that the crest factor is the relation, not the difference?

Crest factor - Wikipedia
Old 1 week ago
  #6
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Slug1's Avatar
Directly from the TT Dynamic Range meter manual.


In order to determine the official DR value, a song or entire album (16 bit, 44.1 kHz wave format) is scanned. A histogram (loudness distribution diagram) is created with a resolution of 0.01 dB. The RMS – an established loudness measurement standard – is determined by gathering approximately 10,000 pieces of loudness information within a time span of 3 seconds (dB/RMS). From this result, only the loudest 20% is used for determining the average loudness of the loud passages.
At the same time, the loudest peak is determined.
The DR Value is the difference between the peak and the top 20 average RMS measurements (top 20 RMS minus Peak = DR).
The top 20 RMS value is not displayed separately. It can be easily calculated in the head by adding the displayed stereo (plus decimal place) DYNAMIC RANGE value with the peak headroom.


The DR bar shows the average difference between peak and RMS and corresponds to
the so‐called crest factor.
Since the bars do not display any static information in order to indicate the top 20 RMS values, in specific situations the indications do not always completely reflect the official values given by the Offline Meter. Keep in mind that the objective is to standardize the "thickness" of a recording and not to measure the overall dynamics.
The variation between the two measurement devices increases as the dynamic range of the material measured is increased. The bars serve to visualize the crest factor.
If you work with more headroom during mixing, a decreasing bar that moves downwards will warn you of too much compression, because the display of the crest factor is independent on the peak room which is used.
Old 1 week ago
  #7
Lives for gear
 

So? My comment to this old thread concerned the Crest factor, not the DR.
In the text you refer, (... "corresponds the Crest factor"), corresponding means (can mean) "is interpreted as the Crest factor".

Both measure the dynamic structure of the audio, both decrease, when the dynamic range of the audio material decreases, and vv., i. e. the same basic interpretation, but calculated totally differently.
Old 1 week ago
  #8
I'd be more strict and say that using the term dynamic range was a mistake in the first place. Not much to argue around that.

Dynamic range is a property of a medium or system.
A signal always has a dynamic range equal to its max peak. So why not call it max peak?
The proper term is crest factor, or peak to average ratio.

There are many types of crest factors, the definition is rather loose. There is not such thing as "one" universal crest factor. But dynamic range has no reasonable meaning in the context of a signal.


A note on the relation vs difference question above:

When expressed in dB, the ratio between 12dB and 6dB is 6dB (the difference, 12 - 6). When expressed in linear values, the ratio between 4 and 2 is 2 (a division, 4 / 2). That's why software engineers love working with the dB scale: It turns multiplications into additions, divisions into subtractions, square roots turn into divisions, etc. The result is equal in either case.
Old 1 week ago
  #9
Lives for gear
 

"I'd be more strict and say that using the term dynamic range was a mistake in the first place. Not much to argue around that."

If so, I wonder who made first that mistake?

I have used the Crest factor, but I have noticed this parallel dualism Crest/DR.
In fact, why I commented this old thread, was the fact thay I did a search to find out, what is the DR all about, the relation and found this in GS.

Your explantion to the Crest factor formula (ratio vs. difference), was too complicated to me.
I refer to the documents, which talk only about the ratio, to which I rely.
Old 1 week ago
  #10
The "ratio" between two decibel values really is A - B (a subtraction).
The ratio between two linear values is A / B (a division).

So, depending on which type of values we talk about, ratio and difference can both be correct.
The ratio between two (linear) values, is equivalent to the difference between the two decibel values.


Say you have 0dB peak level (linear value = 1) and -12dB RMS (linear value ~0.25).
The peak to average ratio or crest factor can be both expressed as:

crestfactor_dB = peak_dB - rms_dB = 0 - -12 = 12

or

crestfactor_lin = peak_lin / rms_lin = 1 / ~0.25 = ~4.0


If you insist on a division, the result of this operation is always a linear value! Most humans don't can't handle linear ratios very well, though. In the context of decibel values, rather common in music, a ratio is achieved by subtraction, i.e. by taking the difference between two decibel values.
Old 1 week ago
  #11
Lives for gear
 

Well, I think I can manage with this, which is intuitive enough:

"Crest factor is the peak amplitude of the waveform divided by the RMS value of the waveform:

C = Peak/RMS

Crest factor - Wikipedia
Old 1 week ago
  #12
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Trakworx's Avatar
The overly simple way I think of it is this:

Crest factor is division. A ratio. Peak divided by RMS

"DR" as (mis)defined by the TT meter is subtraction. A difference. Peak minus RMS.

They are alternate ways of measuring the same thing.

In Bob Katz's book he calls it "microdynamics".
Old 1 week ago
  #13
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Trakworx's Avatar
Also, a newer take on it than the TT meter is Dynameter by Ian Shepherd. Check the video:

Dynameter: Dynamics metering for AAX, AU and VST

"Dynameter displays a measurement called PSR - the difference between the peak level and the loudness."

I believe it uses LUFS to measure the loudness instead of RMS.
Old 1 week ago
  #14
Gear Head
 
uros's Avatar
 

Quote:
Originally Posted by Harry_O View Post
Is this really the case? I believed, that the crest factor is the relation, not the difference?

Crest factor - Wikipedia
You are neglecting the fact that dB is a logarithmic (dimensionless) unit. So, when you say i.e. "the crest factor of the song is 20dB (the difference between a peak and average level in dB)" you are saying that the ratio of of peak to average (RMS) voltage of that particular song is 10:1.

Hope this helps.
Old 1 week ago
  #15
The matter is slightly confusing, but well worth being discussed in depth.


One can imagine many methods to represent a signal.

The most natural one would be a linear mapping. Usually, in floating point digital audio, full scale is represented by 1 (and -1). Linear mapping means that doubling the input will also yield a doubled value. e.g. you enter a 0 into the system and it writes a 0. Same with a 0.5 and you get a 0.5. And so on. This is a linear representation.
Worth noting: It represents a linear ratio relative to a certain reference (i.e. full scale) value.

As mentioned above, human intuition can't handle linear representation well (but algorithms usually do). For these types of signals/measures mathematics developed the concept of nonlinear representation, in our case here, the Decibel, a logarithmically "bended" scale. It allows imagining very large range values without having to memorize dozens of decimal places. It also usually offers a more intuitive perspective into most real world events.
Decibel values also represent a ratio relative to a certain reference (i.e. full scale), but the relation is not linear, not a straight line. e.g. doubling the input via an amp will not double the decibel value. Instead, it will simply increase by roughly 6dB. Mathematically speaking, the amps' multiplication turns into an addition (!).


So far, so good. No let's jump back to the definition of the crest factor, or peak to average ratio:

crest = peak / average

An example:

2.0 = 1.0 / 0.5
1.0 = 1.0 / 1.0
1.0 = 0.5 / 0.5

Now the problem is, the definition above expects linear values. It doesn't work with decibel.
We need a decibel compatible version of this definition, right?

As it turns out, it is simply:

crest_dB = peak_dB - average_dB

e.g.

6.0dB = 0.0dB - -6.0dB
0.0dB = 0.0dB - 0.0dB
0.0dB = -6dB - -6dB

(just to be clear about the point, the above is now a subtraction, i.e. taking the "difference". No more a division)



Most musicians and audio producers only use decibel and rarely even touch linear representation. In that sense, it is totally correct to describe a crest factor as the peak minus the average. In decibel, a ratio is expressed by subtraction.

Last edited by FabienTDR; 1 week ago at 01:27 AM..
Old 1 week ago
  #16
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Greg Reierson's Avatar
 

Verified Member
Can we make that a sticky?

Every discussion on GS and elsewhere about how loud to make a master is really about crest factor. Much more telling than LUFS or RMS or peak values alone.
Old 1 week ago
  #17
Gear Head
 
jontornblom's Avatar
Side note: IMO the best section in Bob Katz's book is the section on how you use calibrated monitor levels to let your ears guide you to the right loudness.
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