Effects

This chapter is from the book

Adobe Audition CC Classroom in a Book, 2nd Edition

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This chapter is from the book

This chapter is from the book 

Adobe Audition CC Classroom in a Book, 2nd Edition

Learn More Buy

Amplitude and Compression effects

Amplitude and Compression effects change levels and alter dynamics. In broad terms, this means the effects in this category change the amplitude of your audio, the speed at which the audio gets louder or quieter, or the way compression is applied.

Amplify

Amplify can make a file louder or softer. When you’re increasing amplitude to make a file louder, choose an amount of amplification that is low enough so that the file remains undistorted.

Channel Mixer

The Channel Mixer alters the amount of left and right channel signal present in the left and right channels. Two possible applications are converting stereo to mono and reversing the left and right channels.

Converting stereo to mono is a common enough operation that the Channel Mixer preset named All Channels 50% performs this conversion. When working in the Multitrack Editor, you’ll discover there’s a Sum to Mono button for every track.

DeEsser

The DeEsser reduces vocal sibilants (“ess” sounds). De-essing is a three-step process: Identify the frequencies where sibilants exist, define that range, and then set a threshold, which if exceeded by a sibilant, automatically reduces the gain within the specified range. This makes the sibilant less prominent while maintaining the clarity of the speech.

Dynamics processing

With a standard amplifier, the relationship between the input and output is linear. In other words, if there’s a gain of 1, the output signal will be the same as the input signal. If there’s a gain of 2, the output signal will have twice the level of the input signal, whatever the input signal level may be.

The Dynamics Processor effect changes the relationship of the output to the input. This change is called compression when a large input signal increase produces only a small output signal increase and expansion when a small input signal increase produces a large output signal increase. Both can be present at the same time by expanding signals within one range of levels and compressing signals in a different range of levels. The Dynamics Processor’s graph shows the input signal on the horizontal axis and the output on the vertical axis.

Compression can make a sound subjectively louder and is the tool that makes TV commercials SO MUCH LOUDER THAN EVERYTHING ELSE. Expansion is less common; one application is to expand objectionable low-level signals (like hiss) to reduce their levels further. There are uses for both as special effects.

The easiest way to become familiar with dynamics processing is to load various presets, listen to how they affect the sound, and correlate what you hear to what you see on the graph.

1. If you have any files open, choose File > Close All.

2. Choose File > Open, navigate to the Lesson04 folder, and open the file Drum+Bass+Arp110.wav.

   The audio has a range of levels and a mix of instruments.

3. In an Effects Rack insert, click the right arrow button, and then choose Amplitude and Compression > Dynamics Processing.

4. Enable looping on the Transport, and then start playback.

5. Choose the 3:1, Expander < 10 dB preset.

   The blue line indicates the new relationship between the input signal (the original audio) and the output signal (the result of the effect).

   With this preset, as the input signal (along the bottom edge) changes from −100 dB to around −40 dB, the output (along the right edge) changes from −100 dB to only −95 dB. As a result, the Dynamics Processor has compressed 60 dB of input dynamic range into 5 dB of change at the output. But from around −40 dB to 0 dB, the output changes from −95 dB to 0 dB. Therefore, the Dynamics Processor has expanded 40 dB of input dynamic range into 95 dB of output dynamic range.

   

   Click to view larger image

   Notice the small square control points on the blue line. You can drag those directly to manually adjust the blue line, which represents the relationship between the input and output signals.

   Each blue line has a tiny segment number, and the area below the graph provides the following information about each segment:

   • The segment number

   • The relationship between output and input expressed as a ratio

   • Whether the segment is an Expander, a Compressor, or Neutral

   • The Threshold (range of levels) where the expansion or compression takes effect

6. Try a few other presets. Note that you will need to turn down the Effects Rack’s Output level when you’re using some of the more aggressive presets to avoid distortion.

7. Try creating your own dynamics processing: Begin by choosing the (Default) preset, which provides neither compression nor expansion.

8. Drag the little white square in the upper right down slowly to around −10 dB. Listen to how this brings down the peaks and makes the sound less dynamic.

9. Create a less abrupt change. Click in the middle of segment 1 (where the segment crosses −15 dB) to create another square. Drag it up a little bit to around −12 dB.

10. Now try expansion to reduce low-level sounds. Click the line at −30 dB and −40 dB to create two more squares. Drag the one at −40 dB all the way down to −100 dB. This effect makes the drums sound more percussive.

    

    Click to view larger image

    NOTE

    There’s no need to close effect windows to playback, access menus or controls, or even apply other effects. Your only limitation is space on your computer screen.

    NOTE

    Basic compression and expansion can solve many audio problems that need dynamics control. The Dynamics Processor is extremely sophisticated, however, and the Settings panel within the effect allows for further customization. Refer to the Audition online Help for detailed information on other Dynamics Processor parameters.

11. Look at the Effects Rack’s Output meter as the audio plays. Bypass the dynamics processing, and you’ll see that the original signal is actually a little louder because the compression you applied has reduced the peaks. To compensate for this, click in the Dynamics Processor’s Make-Up Gain parameter located just below the curve’s horizontal axis to select the value. Increase the gain by +4 dB.

12. Bypass and enable the Dynamics Processor by toggling the Power button for the effect on the Effects Rack . Because you added Make-Up Gain, the processed signal is now a little bit louder.

13. Stop playback, click the Effects Rack insert with the Dynamics Processor, and press Backspace/Delete (no need to close the effect window, as it will close when you delete the effect).

Hard limiter

Like an engine’s governor that limits the maximum number of RPMs, a limiter restricts an audio signal’s maximum output level. For example, if you don’t want an audio file to exceed a level of −10 dB, yet there are some peaks that reach −2 dB, set the limiter’s Maximum Amplitude to −10 dB, and it will “absorb” the peaks so they don’t exceed −10 dB. This is different from simple attenuation (which lowers the levels of all signals), because now levels below −10 dB remain untouched.

Levels above −10 dB will be limited with an essentially infinite ratio, so any input level increase produces no output level above −10 dB. It’s a little like flattening only the highest peak of a mountain range, leaving the rest of the range untouched.

This limiter also has an Input Boost parameter, which can make a signal subjectively louder. Here’s why: If you set the Maximum Amplitude to 0, you can increase the level of an input signal that already reaches the maximum headroom, because the limiter will prevent it from distorting by clamping its output to 0. Listen to how this affects a mix.

1. With the Drums+Bass+Arp110.wav still loaded, click an Effects Rack insert’s right arrow button, and choose Amplitude and Compression > Hard Limiter.

   

   You can use sliders, drag on the blue numbers, or click and type new numbers to update the setting.

2. Enable looping on the Transport, and start playback.

3. The default Maximum Amplitude numeric is −0.1. This ensures that the signal won’t hit zero, so the output won’t trigger the red zone in the Effects Rack panel’s Output level meters.

4. Raise the Input Boost above 0 while observing the Output level meters in the Effects Rack.

   Even if you add lots of boost, like 10 dB, the output still doesn’t go above −0.1, and the Output meters never register red peaks.

   NOTE

   Release Time is an important common control available in a number of effects. It controls the time for which an effect will be applied after it is triggered by a threshold set elsewhere in the effect.

   NOTE

   It’s easy to overdo hard limiting. Past a certain amount of input boost, the sound will become unnatural. The level at which this occurs varies depending on the input signal source. With solo instruments and vocals, you can usually apply more boost than with complex material.

5. The Release Time sets how long it takes for the limiter to stop limiting after a signal no longer exceeds the maximum amplitude. In most cases, the default is fine. With a fair amount of input boost, shorter Release settings might produce a choppy effect, even though they limit the signal more accurately.

6. The Look-Ahead Time setting allows the limiter to react to fast transients. With Look-Ahead Time at 0, the limiter has to react instantly to a transient, which is not possible: It has to know a transient exists before it can decide what to do with it. Look-Ahead alerts the limiter when a transient is coming, so the reaction can be instantaneous. Longer settings cause a slight delay through the effect, although in most cases this doesn’t matter. The default setting is fine, but experiment with increasing the Look-Ahead Time slider if the transients sound mushy.

7. Stop playback after you’ve finished experimenting with these settings.

Single-Band Compressor

The Single-Band Compressor is a “classic” compressor for dynamic range compression and is an excellent choice for learning about how compression works.

As explained in the “Dynamics processing” section, compression changes the relationship between the output signal to the input signal. The two most important parameters are Threshold (the level above which compression starts to occur) and Ratio, which sets the amount of change in the output signal for a given input signal change. For example, with a 4:1 ratio, a 4 dB increase in input level produces a 1 dB increase at the output. With an 8:1 ratio, an 8 dB increase in input level produces a 1 dB increase at the output. In this lesson, you’ll hear how compression affects the sound.

1. If the Drums+Bass+Arp110.wav file is not open, close any other files and open it. Also, delete any currently loaded effects.

2. In any Effects Rack insert, click the right arrow, and choose Amplitude and Compression > Single-Band Compressor.

   

   Click to view larger image

3. Enable looping on the Transport, and start playback.

4. Assuming the Default preset is loaded, move the Threshold slider over its full range. You won’t hear any difference because the Ratio defaults to 1:1, so there’s a linear relationship between the output and input.

5. With Threshold at 0, move the Ratio slider over its full range. Again you won’t hear any difference, because all audio will lie below the Threshold; there’s nothing above the Threshold that can be affected by the Ratio slider. This shows how the Threshold and Ratio controls interrelate, and explains why you usually need to go back and forth between these two controls to dial in the right amount of compression.

6. Set the Threshold slider to −20 dB and the Ratio slider to 1. Slowly increase the Ratio slider by moving it to the right. The farther you move it to the right, the more compressed the sound. Leave the Ratio slider at 10 (meaning 10:1).

7. Experiment with the Threshold slider. The lower the Threshold, the more compressed the sound; below about −20 dB with a Ratio of 10:1, the sound is so compressed it becomes unusable. Leave the Threshold slider at −10 dB for now.

   

   Click to view larger image

8. Look at the Effects Rack panel’s Output meter. When you bypass the Single-Band Compressor, note that the meters are more animated and have more pronounced peaks. Enable the Single-Band Compressor; the signal’s peaks are less dynamic and more uniform.

9. Note the maximum peak level in bypassed mode. Then, with the Single-Band Compressor enabled, adjust its Output Gain control to around 2.5 dB, so its peaks match the same level as when bypassed. Now when you compare the bypassed and enabled states, you’ll hear that despite having the same peak levels, the compressed version sounds louder. The reason is that reducing peaks allows for increasing the overall output gain without exceeding the available headroom or causing distortion.

   It’s possible to make this difference even more pronounced. Attack sets a delay before the compression occurs after a signal exceeds the threshold.

10. Use the default Attack time of 10 ms; this lets through percussive transients up to 10 ms in duration before the compression kicks in and retains some of a signal’s natural percussiveness.

11. Now set the Attack time to 0, and again observe the Output level meters. With 0 Attack time, the peaks have been reduced even further, which means the Single-Band Compressor Output Gain can go even higher.

12. Set the Single-Band Compressor Output Gain to 6 dB. When you enable/bypass the Single-Band Compressor, the peak levels are the same but the compressed version sounds a lot “bigger.”

    

    Click to view larger image

13. Set the release time subjectively for the smoothest, most natural sound, which will usually be between 200 and 1000 ms. The Release setting determines how long it takes for the compression to stop compressing once the signal falls below the threshold.

14. Keep Audition open and loaded with the same file.

Tube-Modeled Compressor

The Tube-Modeled Compressor has the same control complement as the Single-Band Compressor but offers a slightly different, somewhat less crisp sonic character. You can use the same basic steps as in the previous exercise to explore the Tube-Modeled Compressor. The one obvious difference is that the Tube-Modeled Compressor has two meters: The one on the left shows the input signal level, and the one on the right shows how much the gain is being reduced to provide the specified amount of compression.

Multiband Compressor

The Multiband Compressor is a variation on the Single-Band Compressor. It divides the frequency spectrum into four bands, each with its own compressor, so you can compress some frequencies more than others.

Dividing the signal into four bands also embodies elements of equalization (described later), because you can alter a signal’s frequency response.

If you think adjusting a Single-Band Compressor is complex, a Multiband Compressor with four bands isn’t just four times as complex—it’s even more so, because all the bands also interact with each other. One of the best ways to become familiar with the Multiband Compressor controls is to load multiple presets, and then see and hear the results.

Each band has an S (Solo) button; click one to hear what that band alone is doing.

Speech Volume Leveler

The Speech Volume Leveler incorporates three processors—leveling, compression, and gating—to even out level variations with narration, as well as reduce background noise with some signals.