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Signal Processing in Adobe Audition CC

Chapter Description

This excerpt from Adobe Audition CC Classroom in a Book shows you how to use the Effects Rack to create chains of effects, apply effects to audio, adjust parameters in various effects to process audio in specific ways, alter dynamics, frequency response, ambience, stereo imaging, and many other audio attributes, use the Preview Editor to see how a waveform will be altered by an effect before you apply the effect, simulate guitar amp and effects setups with Guitar Suite effects, load third-party, plug-in effects on Mac or Windows computers, apply single effects rapidly without the Effects Rack by using the Effects menu, and create favorite presets you can apply immediately to audio.

Filter and EQ effects

Equalization is an extremely important effect for adjusting tonality. For example, you can “brighten” muffled narration by boosting the treble or make tinny, thin-sounding voices sound fuller by increasing the low frequencies. Equalization can also help differentiate among different instruments; for example, bass guitar and a drum kit’s kick drum both occupy the low frequencies and can interact in a way that makes each one less distinct. To solve this problem, some engineers might emphasize the bass’s highs to bring out pick and string noise, whereas others boost highs on the kick to bring out the “thwack” of the beater.

Adobe Audition has five different equalizer effects; each is used for different purposes that can adjust tonality and solve frequency-response related problems: Parametric Equalizer, Graphic Equalizer, FFT (Fast Fourier Transform) Filter, Notch Filter, and Scientific Filter.

Parametric Equalizer

The Parametric Equalizer offers nine stages of equalization. Five stages have a parametric response, which can boost (make more prominent) or cut (make less prominent) specific ranges (“bands”) of the frequency spectrum. Each parametric equalization stage has three parameters.

Caution: In the following lesson, keep monitor levels down as you make adjustments. The Parametric Equalizer is capable of high amounts of gain at the selected frequencies.

  1. Choose File > Open, navigate to the Lesson04 folder, and open the file Drums+Bass+Arp110.wav.
  2. In any Effects Rack insert, click the right arrow, and choose Filter and EQ > Parametric Equalizer. Start playback.
  3. Note the five numbered boxes. Each represents a controllable parametric stage. Click one of them (e.g., 3) and drag up to boost response, or drag down to cut the response. Drag left to affect lower frequencies or right to affect higher frequencies. Listen to how this changes the sound.
  4. In the area below the graph, each parametric stage shows the Frequency, Gain, and Q/Width parameters. Click on the selected stage’s Q/Width parameter and drag up to narrow the range affected by the boost or cut, or drag down to widen the range. You can also click on the stage’s number to toggle that stage on or off.
  5. Load the Default preset to restore the EQ to having no effect. The L and H squares control a low shelf and high shelf response, respectively. This starts boosting or cutting at the selected frequency, but the boost or cut extends outward toward the extremes of the audio spectrum. Past a certain frequency, the response hits a “shelf” equal to the maximum amount of cut.
  6. Click on the H box and drag it up slightly. Note how this increases the treble. Now drag it to the left, and you’ll hear that the boost now affects a wider range of high frequencies. Similarly, click on the L box to hear how this affects the low frequencies. In the Parameter section for the Low and High shelf sections, you can click the Q/Width button to change the steepness of the shelf’s slope.
  7. Reload the Default preset so the EQ has no effect. There are two additional stages, Highpass and Lowpass, which you enable by clicking the HP and LP buttons, respectively. Click those buttons now.

    A Highpass response progressively reduces response below a certain frequency (called the cutoff frequency); the lower the frequency is below the cutoff, the greater the reduction. A Highpass filter is helpful for removing subsonic (very low-frequency) energy.

  8. Click on the HP box and drag it to the right to hear how it affects low frequencies.
  9. You can also change the filter slope’s steepness, in other words, the rate of attenuation compared to frequency. In the HP panel that displays its parameters, click the Gain drop-down menu and choose 6dB/octave. Note how this creates a gradual curve. Then select 48dB/octave to produce a steep curve.
  10. Similarly, listen to how the Lowpass filter affects the sound by clicking and dragging the LP box left or right, and choosing different curves from the Gain menu. Keep this project open for the next lesson.

    All of these responses are available simultaneously. The screen shot shows a steep Highpass slope, a slight parametric boost with stage 2, a narrow parametric cut with stage 3, and a High shelf boost.

Graphic Equalizer (10 Bands)

A Graphic Equalizer can boost or cut with a fixed bandwidth at various fixed frequencies. It gets its name because moving the sliders creates a “graph” of the filter’s frequency response.

Caution: In the following lesson, keep monitor levels down as you make adjustments. The Graphic Equalizer can produce high amounts of gain at specific frequencies.

  1. Assuming Audition is still open and the file Drum+Bass+Arp110.wav is still loaded, click the right arrow of the insert that had the Parametric Equalizer loaded, and choose Filter and EQ > Graphic Equalizer (10 Bands).
  2. Start playback if necessary. Move the various sliders up and down to hear how each affects the timbre by varying the level within their respective frequency bands. In musical terms, each slider is an octave apart. Keep the project open in preparation for the next lesson.

Graphic Equalizer (20 Bands)

The Graphic Equalizer (20 Bands) works identically to the Graphic Equalizer (10 Bands) except the bands are half an octave apart, which provides greater resolution. To hear how it works, follow the same basic procedure as the lesson for the 10 Bands version.

Graphic Equalizer (30 Bands)

The Graphic Equalizer (30 Bands) works identically to the Graphic Equalizer (20 Bands) except the bands are a third of an octave apart, which provides greater resolution. To hear how it works, follow the same basic procedure as the lesson for the 10 Bands version.

FFT Filter

The FFT Filter is an extremely flexible filter that lets you “draw” the frequency response. The default settings are a practical point of departure. FFT is a highly efficient algorithm commonly used for frequency analysis.

  1. Click the right arrow of the insert that had a Graphic Equalizer loaded, and choose Filter and EQ > FFT Filter.
  2. Start playback. Click on the graph to create a point; the blue line that indicates frequency response will move up or down as needed to “snap” to that point. You can then drag this point up, down, or sideways. You are not limited to the number of points you can add, which allows you to make very complex—and even truly bizarre—EQ curves and shapes.
  3. For a smoother curve, enable Spline Curves. The upper screen shot shows Spline Curves deselected and the original placement of points, whereas the lower screen shot shows Spline Curves selected.

Notch Filter

The Notch Filter is optimized to remove very specific frequencies in an audio file, like a particular resonance or AC hum. However, Audition also has a filter optimized specifically for removing hum; this is covered in Chapter 5, “Audio Restoration.”

  1. Choose File > Open, navigate to the Lesson04 folder, and open the file ReduceHum.wav.
  2. Start playback. Note the huge amount of hum in the file.
  3. Click an effect insert’s right arrow, and choose Filter and EQ > Notch Filter.
  4. Enable the Notch Filter as the file plays back. The filter’s default setting is a good start (Europeans should select the 50Hz and Harmonics Removal preset instead of the 60Hz-based default), but note that there’s some ringing and an unnatural quality. You’ll now tweak the settings to reduce hum while retaining a natural sound.
  5. There are six notches starting at 60Hz whose frequencies are set to harmonics of 60Hz. Turn off all notches that don’t improve the sound by clicking a notch’s enable button. Turn off notches 3, 4, 5, and 6. Note that this doesn’t increase the amount of hum. Turn off notches 1 and 2. These contribute hum, so re-enable them, and let’s work on optimizing these.
  6. Reduce the gain for notches 1 and 2 to around -45dB.
  7. Experiment with the Gain parameters for notches 1 and 2. For the most natural sound, you want to use the least amount of reduction consistent with reducing hum. You’ll probably be able to reduce hum sufficiently with about -36dB of cut.
  8. Bypass the Notch Filter, and note how the hum increases.

Scientific Filter

Scientific Filters are commonly used for data acquisition, but they have audio applications as well—such as creating extremely steep slopes, narrow notches, ultra-sharp peaks, and other highly precise filter responses. The trade-off is that this precision can compromise other aspects of filtering (for the technically minded, these include phase shift and delay through the filter); however these trade-offs resemble the trade-offs inherent in analog filter technology, and some people prefer this kind of sonic “character.”

There are four different Scientific Filter types, and each type offers four modes. Of these, the Butterworth response is generally the best compromise between quality and precision.

The available parameters depend on the selected filter type and mode. Because the Scientific Filter is computationally intensive, you won’t hear any difference as you alter most parameters; once you stop adjusting the parameter, the Scientific Filter finishes its calculations and you can hear the results of your edits. Also, note that several parameters cannot be adjusted unless playback is stopped.

Because the Scientific Filter is relatively complex, an easy way to find out how it can affect the sound is to load different presets and vary some of the parameters.

  1. Choose File > Open, navigate to the Lesson04 folder, and open the file DeepTechHouse.wav.
  2. Click an effect insert’s right arrow, and choose Filter and EQ > Scientific Filter.
  3. Start playback. Select the Drop Off Below 250Hz preset. Note the steep slope that eliminates all the bass. To make this even steeper, increase Order to 66; the higher the order, the steeper the slope.
  4. Stop playback, and then adjust Cutoff to 500Hz. Resume playback. The sound is even “tinnier,” and all the bass is gone.
  5. Change Modes to LowPass and you’ll hear the reverse—all bass and no treble. Change Modes again to BandPass, and the Scientific Filter removes all frequencies except for a particular band of frequencies.
  6. Stop playback, click on High Cutoff, and type 1000. Start playback, and you’ll hear just a tiny slice of frequencies. Change Modes to BandStop, and the reverse occurs: A slice of frequencies within the band is removed.
  7. Stop playback, and select the Remove Subsonic Rumble preset. Start playback by pressing the spacebar, and you won’t hear any loss of bass because the response drops dramatically below 28Hz. This filter response can be very useful if a signal has subsonic “mud” that interferes with sounds in the audio range.
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