Assignment for Week 4 of Introduction to Music Production on-line course offered by Coursera

1. Hi. My name is Jan Zurcher.
I’m a singer-songwriter living in a
small town called Friday Harbor, San
Juan Island, Washington
This lesson is for Week 4 of the
Introduction to Music Production
Course at Coursera.org.
The topic I have chosen to look at
this week is…

3. Dynamic Processors are used to control the dynamic range of a recording
• to enhance the highs and/or lows of your tracks to make the recording
more exciting or to emphasize a particular part of a song;
• to reduce the highs and/or the lows;
• to make the amplitude more consistent;
• to eliminate unwanted noise; or,
• to adjust the transients (loud sounds at the start of a sound)
Use of Dynamic Processors

4. Dynamic Range
Dynamic range is the difference between the loudest and the quietest sounds. You could say
that the dynamic range is represented by the red line shown above.
However, if you tried to analyse the signal above by finding the average volume, you would end
up with an average of 0 because the wave spends as much time about the 0 mark as below it.
For this reason, dynamic processors often use the RMS (Root Mean Squared) measured in dB
with 0 as one point of reference and -70 dB as another to determine the average loudness of a
signal.
When you record a sound in your DAW, you get a wave form that looks something like this:

5. Dynamic Range
A larger segment of the audio recording looks like this:
If this wave form were converted into an RMS curve, the result would look something
like this:
Here you can see that the (uncompressed) range is from -54.0 dB to +4.5 dB (or a
dynamic range of 58.5 dB).

6. Dynamic Range
A common way that you see the dynamic range represented in your DAW is on the fader
meter where the scale ranges from +6 dB to around -70 dB (which is basically zero
sound).
For another segment of the above audio signal captured in a screen shot, the loudest
point was +1.8 dB and the lowest was -33.6 dB (or a dynamic range of 35.4 dB as
depicted by the red arrow).
Dynamic Range

7. Common Types of Dynamic Processors
Compressor
Expander
Limiter Noise Gate
Dynamic range can be changed using any of a number of devices called Dynamic Processors
including (but not limited to): Compressors, Expanders, Limiters and Noise Gates.
Shown here are screen shots of some of the built-in Dynamic Processors in Logic Express 9.0.

8. Key Components of Dynamic Processors
Although each of these dynamic processors creates changes in dynamic range
a little differently, they have some common components and work on some
common principles.
First, each of these is basically divided into two sections – one section analyses
the input signal to find the shape of the sound envelop (the RMS discussed
above). This is called the “side chain section” (or key section).
The other section contains the volume fader that is used to make adjustments
in the audio level – either up or down as needed. There are also a number of
other factors that can be adjusted to create the type of dynamic range that
you want.

9. Common Elements of Dynamic Processors
These other adjustment factors include :
Threshold: The volume level at which the dynamic processor begins to
affect the signal
Ratio: How much the input volume is changed as a proportion of
output level over the threshold
Attack: How fast the processor begins to alter the signal once the
threshold is reached.
Release How fast the processor stops altering the signal once the
threshold is crossed back into the acceptable range
Let’s take a closer look at what each of these terms mean when it comes to
processing an audio signal. In each case, the examples are assuming the
use of a downward compressor.

10. Input Level (dB)
In this example, the threshold is set at -20 dB. This threshold can be adjusted to
whatever input level you need for the effect you want. A threshold set at -60 dB will
affect the entire signal. A threshold of 0 dB would not affect any of the signal.
-60 -50 -40 -30 -20 -10
Threshold
For downward compression, when the input level of an audio signal goes above a
specified point (called the threshold), gain reduction begins.
Threshold Level – Downward Compression

11. Input Level (dB)
-60 -50 -40 -30 -20 -10
-10
-30
-20
-40
-50
-60
Once you have told the compressor the input level at which it should start processing
the signal (that is, the threshold level), you next need to let it know how much you
want it to reduce the gain.
This is determined by the ratio. If you set the ratio to 1:1. Even if the threshold is
crossed, there will be no gain reduction because the ratio of 1:1 indicates that the
output level should equal the input level.
OutputLevel(dB)
Compression Ratio

12. Input Level (dB)
-60 -50 -40 -30 -20 -10
If you select a ratio of 2:1, after the threshold is crossed, if the input level is 20 dB
over the threshold level, the output level will be reduced so that it is only 10 dB
over the threshold level.
-10
-30
-20
-40
-50
-60
OutputLevel(dB)
Reduction in output gain

13. Input Level (dB)
-60 -50 -40 -30 -20 -10
-10
-30
-20
-40
-50
-60
OutputLevel(dB)
Input Level (dB)
-60 -50 -40 -30 -20 -10
-10
-30
-20
-40
-50
-60
OutputLevel(dB)
The threshold level and the ratio work together to establish how much reduction
in the gain of the output signal there will be.
In this example, with a -30 dB
threshold and a 2:1 ratio, the gain
reduction is 15 dB.
In this example, with a -50 dB
threshold and a 2:1 ratio, the gain
reduction is 25 dB.
Reduction
in gain Reduction
in gain

14. Input Level (dB)
-60 -50 -40 -30 -20 -10
-10
-30
-20
-40
-50
-60
OutputLevel(dB)
Input Level (dB)
-60 -50 -40 -30 -20 -10
-10
-30
-20
-40
-50
-60
OutputLevel(dB)
For downward compression, as the ratio gets larger, the amount of gain reduction
increases until finally, at a ratio of Infinity:1, the output level of the signal will be
the same as the threshold level.
At that point, the compressor is acting just like a limiter – limiting the level of the
output signal to the threshold level.
In this example, with a -40 dB
threshold and a 4:1 ratio, the gain
reduction is 30 dB.
In this example, with a -50 dB
threshold and a 40:1 ratio, the gain
reduction is 39 dB.
Reduction
in gain Reduction
in gain

15. Once you have told the device the threshold level and the relative
amount that you want the output signal to be reduced, the next step
is to tell it how quickly you want it to react when it detects that the
threshold has been crossed.
This is known as the Attack Phase which is how long it takes the
processor to decrease the gain down to the level established by the
ratio.
This attack time is measured in milliseconds (ms) and can be set to be
very fast ( < 1 ms) or relatively slow ( > 100 ms).
Compressors in Logic Express 9.0 allow adjustments in attack from 0
ms to 200 ms in 0.5 ms intervals.
Attack Time

16. Fast attack results in the gain being reduced almost instantly as soon as the
threshold is crossed. This may not be what you want because that transient
information at the beginning of a sound adds significantly to the character
of that sound. Reducing it right away can lead to a dull sound.
On the other hand, if the attack time is set too slow, the dynamic processor
may act too late and be less effective.
Input Level
Output Level
Time (ms)
dB
Input Level
Output Level
Time (ms)
dB
Attack PhaseAttack
Phase
Fast Attack Slow Attack
Threshold Threshold

17. Release Time
The final common function found in dynamic processors covered in
this presentation is the Release Phase.
Just as you have to tell the device how fast to reduce the gain to the
required level once the threshold is reached, you also need to tell it
how fast to return to the input level once the threshold is crossed in
the opposite direction.
The Release Time is measured in milliseconds (ms) and can be set to
be fast ( < 5 ms) or relatively slow ( > 5,000 ms).
Compressors in Logic Express 9.0 allow adjustments in release from 5
ms to 5000 ms.

18. A fast release time means the signal returns to match the input level almost
immediately after the threshold is crossed. You might want to use a lower
release time if you want to make dynamic differences stand out.
On the other hand, if the release time is set to a larger number of
milliseconds, the dynamic differences in the signal will be more smoothed
out – that is a gradual return to the input level.
Input Level
Output Level
Time (ms)
dB
Input Level
Output Level
Time (ms)
dB
Release PhaseRelease Phase
Fast Release Slow Release
Threshold Threshold

19. Dynamic Processors - Summary
This concludes this brief overview of the concept of Dynamic
Processors and the four common elements that these types of
processors have in common – that is threshold, ratio, attack and
release.
Although the details of the explanations were provided in the
context of how these work in a compressor, these common
elements operate in similar ways in other common types of
Dynamic Compressors including Limiters, Expanders and Noise
Gates.