Sound Advice: Digital Audio Effects

Last month, we talked about recording and editing sound effects for your video productions. Just briefly, we mentioned spicing up your recordings with echo, chorus and reverb. This month, we’ll explore these and other processing options in more detail. Used in moderation, these effects reinforce your audio image. Used to excess, they often muddy the water and take the focus off your story.

Reverb

The granddaddy of all audio effects, reverberation adds a sense of space to your sounds. Whether applied in an audio-only program or your video editing software, reverb simulates an audio environment using small bits of computer programming called “algorithms.” Reverbs are based on three major types of algorithms: plate, room and hall. The plate reverb is named for the analog electro-mechanical device it is based on. Back in the old days, springs suspended a large plate of thin metal. A transducer attached to the plate and pumped in audio signals, making the plate reverberate. A pickup device was attached to hear the reverb, with the resulting signal mixed into recordings to simulate an acoustic space. Plate reverbs (real or virtual) are renowned for their complimentary sound on vocals, percussion and drums.

Room and hall algorithms simulate the space they’re named for. Room sounds are more confined, representing everything from a shower stall to a classroom. Hall reverbs emulate the acoustic properties of performance venues from small recital rooms all the way up to Carnegie Hall.

Reverb plug-ins have several adjustable settings. First is the room size or decay time. This setting determines how long the reverberated sound takes to die out. The second setting, called “brightness” or “damping,” determines how much high frequency your reverb allows (the bigger the room, the less high-frequency content). Another common setting is pre-delay. This determines how long the original sound takes to hit the virtual walls and will radically change the space of your reverb. The diffusion adjustment controls whether your reverb is smooth or full of echoes.

Echo and Delay

Echo and its cousin, delay, are popular effects in music production and special effects editing. Delay is a single repetition of audio that just occurred. The main adjustments are the amount of time in the delay most often measured in milliseconds and a ratio of original to delayed sound.

Echo builds on the simple delay by adding regeneration or feedback to the mix. An adjustable amount of the delayed sound mixes back into the signal, creating multiple echoes. Multi-tap is another variant. This echo type includes several separate delay lengths, each with its own adjustable settings. All the echoes blend into the sound, creating a complex mix. Multi-taps often include the ability to send the sound of a specific tap to the left or right channel of a stereo mix. Adobe Premiere includes an excellent Multi-tap delay that even offers a tempo calculator to match the echoes to the beat of your soundtrack.

Chorus and Flange

Also popular in music production, chorus and flange are unique tools that take simple delays to a whole new level. Chorusing uses a very short delay (around 25 milliseconds) and combines it with regenerating feedback, and then fades the effect in and out over the span of a quarter-second or so. The resulting audio sounds as if several separate sounds are playing at the same time, much like a chorus of singers. The chorus effect is common on guitar sounds, but also adds a unique smearing of specialty sound effects.

Flanging is very similar to chorusing, without the addition of feedback. The delay time is shorter (5 to 15 milliseconds) and the affected sound has a whooshing character. Darth Vader’s electronically assisted voice used flanging to produce its menacing effect.

Pitch Shifting

Pitch shifting, a versatile effect, can transform one voice into another or turn a cannon shot into a huge explosion. With the right software, you can even simulate a tape recorder with dying batteries, running slower and slower over time. Most often, pitch shifting applies to audio editing and music software. Syntrillium’s Cool Edit 2000 has an excellent time/pitch effect that lets you shift the pitch, alter the duration of the audio or both.

In the video editing arena, you can change the duration of an audio or video clip to create a pitch shift. Based on a percentage of the original clip, 125 percent is a higher pitch, 75 percent is a lower pitch. Some applications, such as Vegas Video, allow you to change the duration without changing the pitch, within reasonable limits.

Available Effects

The effects available to you vary by software and type. Within a given audio or video editing program, there are many built-in effects. They range from simple to complex, and sound quality varies from stellar to worthless. It’s a bit of a mixed bag and you’ll have to spend some time experimenting with the numerous effects and all their variations. Premiere’s Multitap delay is an excellent example. It is a well-designed, functional tool.

Most Windows audio programs (and several video packages) offer support for DirectX plug-in effects. These are small add-on programs that provide all the standard audio effects. If the built-in reverb program doesn’t suit your project, try a plug-in. There are several excellent audio effects available in the DirectX format. Many rival the sound quality of stand-alone equipment that costs thousands of dollars. You may already have several DirectX plug-ins installed on your computer. If you have dedicated audio editing or music production software, those programs likely installed some bundled plug-ins. The AnalogX Web site (www.analogx.com) offers a great tool for managing your DirectX plug-ins, called “DXman.” It’s a free download and will help you install, uninstall and keep track of all of your available audio effects.

When and Where

So, when is the right time to apply effects? Should you add the spice in a dedicated audio editor or in your video editing software? The answer depends on your project, the level of control your software allows and how soon you want to commit to the final sound. An audio-only program optimizes for just that, audio, so it’s safe to assume a high degree of control and flexibility. The drawback is that you must decide on the final adjustments before dropping the audio into the timeline of your video project. For sound effects, this isn’t a problem, but for dialog and other critical elements, you may choose to reserve final adjustments for the video editing environment.

By comparison, video editing software sometimes offers limited control over audio effects. However, these applications have come a long way in just a few years. Premiere now offers a virtual mixer and support for Direct-X plug-ins along with standard volume and panning tools. Vegas Video really shines in this area. It started life as an audio application, adding video editing features when it went to version 3. The user interface offers many of the sophisticated audio tools available in Sonic Foundry’s Sound Forge.

By saving your audio effects for the video timeline, you gain the power to make small but powerful changes to transform the finished audio.

One Last Tweak

Audio effects are power tools and you should treat them as such. It’s simple to apply some nice effects to polish your production. It’s equally as simple to ruin a perfectly good soundtrack with too much processing. Another reminder that less is more. Spend some time learning the strengths and weaknesses of the various effects. Get familiar with how much is too much and when it’s just right. The time invested will take your audio production to the next level.

[Sidebar: Sunday, Sunday, Sunday!]

We’ve all heard it screamed from the TV to herald an upcoming monster truck or super-cross event. Although more irritating than professional, these commercials are a smorgasbord of audio processing and effects, and they really do grab your attention. In the span of 30 or 60 seconds, you’ll hear textbook examples of all the effects we’ve outlined: reverb, echo, delay, chorus, flange and pitch shifting. So, if you’re looking for some practical application for your newfound audio tools, sit back and watch a little TV. Better yet, record the commercials for reference.

[Sidebar: Wax On, Wax Off]

Anyone can see the results of a video filter instantly, but it is easy to get lost when you use audio effects and forget what the original sounded like. Make sure you constantly turn the audio effects filters on and off to compare your changes with the original.

[Sidebar: Very Effective]
Plug-in effects are addictive. Once you experience their power and flexibility, you simply must have more. Fortunately, there are many freeware and shareware plug-ins available on the Internet. A quick check with your favorite search engine will reveal many plug-ins, but there are huge effects repositories if you know where to find them. The first place to start is www.directxfiles.com, a site kindly offered by the Cakewalk audio software folks. Another great place to look is www.hitsquad.com. This site has thousands of audio oriented programs, including a section dedicated to DirectX effects plug-ins.

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