Probably the most popular effect in audio editing is reverberation. You have probably listened to commercial music recordings where the reverb was laid on too thick and it sounds like the singer is being crushed under layer upon layer of reverb or like the recording was made in an empty swimming pool. A little reverb goes a long way. The usual purpose of reverb is to better simulate a live sound, but of course you can do whatever you like. Reverb can sound ethereal and distant and be evocative of things half remembered.

Audacity’s Gverb plug-in is cross-platform and has a Preview button so you can easily try different settings. You should preview reverb settings on monitor speakers rather than headphones, because the channel separation in headphones will lessen the reverb effect.

There are several ways to approach applying reverb to your audio tracks. A common technique is to work from a duplicate wet track rather than your original, unmodified dry track. When you have tweaked your reverb satisfactorily, mix the wet track together with a copy of the dry track. Keeping an original, 100 percent dry track means you can make several reverb tracks with different settings and control the final results in the mix.

You can also edit just a duplicate track, keeping the original for insurance in case the copy becomes a muddled mess. If you are daring, you can work without a net and operate on your original. Audacity has nearly unlimited undo, so this isn’t all that daring, but bad things can happen and then you have extra work.

First select a portion of audio or the whole track. To start from neutral with Gverb, push all sliders all the way to the left (Figure 11-22), except the Dry signal level, which should be at zero.

Figure 11-22. Gverb with all the settings at neutral, or no reverb

Now you can try the settings and hear what they do. The most noticeable changes come from the Early reflection level and Dry signal level settings. Next give Tail level a go, keeping it at an equal or lesser value than Early reflection level, and then try changing Reverb time. This is what each setting does:

The Audacity manual suggests a number of prefab settings to try (http://wiki.audacityteam.org/index.php?title=GVerb), which I have copied here:

Freeverb is an older reverb plug-in that is a bit simpler to use, and to my ears it sounds better (Figure 11-23). The Room Size slider has a wide and obvious range, and there are both Wet and Dry sliders. Width mimics speaker spread. Check the “Freeze Mode” checkbox to play the preview dry without changing your Freeverb settings so you can quickly compare it to the modified signal.

Figure 11-23. Freeverb is an another reverb effect.

If Freeverb doesn’t come with your Audacity installation, visit the Freeverb3 home on SourceForge to get both source code and binary files (http://freeverb3.sourceforge.net/).

Now let’s look at the built-in Audacity Effect plug-ins.

I use the Effect > Amplify effect a lot for both reducing and increasing amplitude. Don’t check “Allow clipping” or go over zero unless you know you really want to, because anything greater will be clipped and distorted. An increase of 3 dB is double, and 1 dB is about the smallest change we can perceive. Enter a negative value, such as -3 dB, to reduce amplitude. Amplify can be applied to a selection, a whole track, or a group of tracks.

This is a great effect for recordings with a background music track, such as a podcast, because it automatically lowers the volume when the foreground track cuts in and raises it when the foreground cuts out. In Figure 11-24, we see the setup: On top is a stereo background music track, and the bottom mono track is a spoken-voice track. When the voice starts, I want the music volume to decrease, and when the voice stops, the music should return to its former volume level. They have to be in this order: the background track on top and the control track underneath.

Figure 11-24. Using Auto Duck, with your background track on top and your foreground, or ontrol track, underneath

Select the background track, and click Effect > Auto Duck. You’ll see a control panel like the one in Figure 11-25, which shows the settings I like to use. These settings create a fast fade-out and a gradual fade-in. The background track ducks out of the way fast and gracefully glides slowly back in with just a little bit of overlap with the voice track.

Duck amount is how much volume reduction you want on the background track.

Maximum pause determines how long the total fade-ins and fade-outs will take. The Outer fade down length and Outer fade up length values cannot total more than the Maximum pause value.

The Outer fade down length setting determines how quickly the background track will fade before the voice on the control track comes back. Anything outside the two vertical lines in the graph happens when the control track is below your threshold. The Inner fade down length setting determines how much overlap there will be with the control track.

The Outer fade up length setting controls how fast the backing track fades back in when the voice on the control track stops, and the Inner fade up length setting controls the overlap. A half second of gently rising music over the voice isn’t a lot; I think it makes a nice bit of a transition. Figure 11-26 shows what these tracks look like after the Auto Duck effect is applied.

Figure 11-25. Example Auto Duck settings for a fast fade-out and slower fade-in

Figure 11-26. Auto Duck has been applied; compare this to Figure 11-24.

The Threshold setting controls the sound level for triggering the Auto Duck effect.

Change Pitch changes the pitch without changing the tempo, so you can adjust your audio higher or lower in pitch without speeding it up or slowing it down. I’ve used this on tracks that were a little bit out of tune, and it does a nice job. The Change Pitch effect will do its best to detect the current frequency and pitch of your selection, and then you can go up or down from there (Figure 11-27). There are all kinds of digital tuners for instruments and voice that do this and even fancy rackmount units that automatically correct the pitch for you.

Figure 11-27. The Change Pitch effect serves up several ways to measure pitch changes.

Using Effect > Phaser splits the signal into two parts (one wet and one dry), applies your settings to the wet track, and then combines them back into one. Its primary purpose is to create an oscillating or vibrato effect, and thanks to the wonder of modern electronics, you can apply a multitude of extra effects to it. Try it on a recording of your own voice or a plain sine wave to get an idea of what it can do. The phaser (phase shifter) is a popular effect used in all kinds of music: to create a soaring effect on electric guitars, to sweeten keyboards, and to make all kinds of spacey science-fiction noises (Figure 11-28). (A similar effect is the flanger, which you get when you install the extra plug-ins from the Audacity website.)

Figure 11-28. The Phaser effect creates a multitude of fascinating and eerie sounds, from soaring vocals to space aliens.

The Stages setting determines the number of filters used at one time, from 2 to 24. Higher values create a more complex, layered tone, with multiple oscillations.

The Dry/Wet balance accepts values from 0 to 255, with 0 being completely dry and 255 completely wet.

An LFO frequency is a low-frequency oscillation that creates a pulsing rhythm or vibrato-type effect. In the Phaser dialog, the available LFO Frequency range is from 1 to 40 Hz, or 1 to 40 pulses per second. Increasing the value of this setting can have a dramatic effect, depending on the other settings and how it interacts with them. For example, try setting both LFO Frequency and Depth to their maximums and see what happens. You know how ripples in a swimming pool spread out, bounce off the sides, bounce back, and collide with each other? Sound waves do the same thing, and you can’t always predict the results. It may help to keep in mind that sound waves are three-dimensional, so they’re all over the place and not just on a fairly flat plane like water ripples.

Figure 11-29. Phase shift is measured in degrees of a circle.

LFO Start Phase determines the phase shift of your signal, from 0 to 359 degrees. That’s right, just like a circle. The degree of phase shift is most easily explained by looking at Figure 11-29. A sine wave alternates smoothly between positive and negative voltage; positive voltage is above the center line, and negative voltage is below. Where the waveform crosses the center line is the zero crossing point, because that is the point of zero voltage. The starting point of the sine wave is zero rising to positive; 180 degrees is at zero crossing into negative. When it gets back to zero from negative, that is a full 360 degrees.

You might recall from earlier in this chapter how this affects your audio signal: Two waveforms at a phase shift of 180 degrees from each other cancel each other out, and varying degrees of phase shift combine to create different sounds, from a simple echo to weird space alien noises.

You can also illustrate this three-dimensionally with a Slinky. That’s right, Slinky is more than a toy—Slinky is a physics teaching tool. Slinky is a helix, and Slinky represents audio phase in three dimensions. Slinky ripples in longitudinal waves just like sound and in traverse waves that are like the stretched strings of musical instruments. Slinky illustrates harmonics and amplitude. Slinky is amazing, and researching “physics of Slinky” will lead you to all sorts of fascinating knowledge (Figure 11-30).

Depth usually refers to how much the pitch is bent, from 0 to 255, with higher values producing a more pronounced vibrato effect. However, Audacity’s phaser seems to bend the amplitude rather than the pitch, which makes a signal that fades in and out quickly. Crank this up along with the Stages value to get some neat space alien sounds.

Finally, Feedback is the familiar distortion effect that adds crunch and texture. A higher percentage equals more distortion. Set the Dry/Wet balance and Feedback value to the maximum to generate some really weird sci-fi sounds like they used in old movies.

Figure 11-30. Slinky illustrates many attributes of sound waves. (Image Credit: Created by Wikipedia user Roger McLassus, released under the GFDL.)

Reverse is a simple effect with no options—it turns your audio around backward. Back in the 1970s when disapproving pruney-lipped people were playing LPs backward to find the Satanic messages, this would have saved them a lot of trouble. It was a waste of time anyway, since records with devil messages played them frontward.

This is a fun new effect that changes tempo or pitch, or both. But that’s not all—it also has a sliding effect so you can go from slow to fast, lower to higher pitch, both at the same time, and the reverse. I know, all of these effects have been done before in the wonderful Looney Tunes and Merrie Melodies cartoons. But they had to do it the hard way with expensive equipment.

Checking the Dynamic Transient Sharpening checkbox seems to result in a wider dynamic range with a bit less distortion. Overdoing Sliding Time Scale/Pitch Shift will create distortion, and it’s a horsepower hog—on old, slow PCs it will take a long time.

Just like the name says, this makes your signal go “wah-wah.” Maybe I’m easily amused, but exaggerated WahWah effects applied to nice, ordinary music tracks crack me up every time. On a more serious note, the WahWah effect makes an instrument sound like a voice. One of the most famous uses of this effect is on Frampton Comes Alive for the song “Do You Feel Like We Do.” (Admit it, you still own the vinyl double set and take it out and play it once in a while. Don’t be embarrassed; it’s a great album, and Mr. Frampton is a fine guitarist.) Another standout use of WahWah is in Steely Dan’s “Haitian Divorce” on the Royal Scam album, which gives the lead guitar a sarcastic voice.

WahWah is similar to phase shifting. It uses LFO to set the oscillations per second, from 0.1 to 4 Hz. That’s right, point one to four, a lot slower than the Phaser effect.

LFO Start Phase and Depth are just like the settings in the Phaser effect.

Figure 11-31. The WahWah effect makes instruments "talk" and plays tricks with left-right channel balance.

Resonance accentuates the higher frequencies; 1 is least effect, and 10 is the most pronounced.

Wah Frequency Offset emphasizes the lower frequencies at lower percentage settings and emphasizes the higher frequencies at the higher settings. It will cause clipping if you go too high (Figure 11-31).

The WahWah effect adjusts the phase of the left and right channels on a stereo track, making the track sound as though it travels back and forth between the speakers.

Now let’s take a look at finding and managing Audacity plug-ins in Linux and Windows.