Chapter 9 Main Points ► Before taking creative liberties, learn the craft. Train the ear to what the original audio should sound like and then proceed to thoroughly familiarize yourself with how specific settings on a particular signal processor alter that sound. ► Signal processors are used to alter some characteristic of a sound. They can be grouped into four categories: spectrum; time; dynamic, or amplitude; and noise. ► A plug-in is an add-on software tool that gives a digital audio workstation (DAW) signal-processing alternatives beyond what the original system provides. ► Plug-ins incorporated into DAWs add to digital signal processing (DSP) not only the familiar processing tools—equalization (EQ), compression and expansion, reverb, delay, pitch shifting, and so on—but also an array of capabilities that place at the recordist’s fingertips virtually limitless potential for creating entirely new effects at comparatively little cost. ► Plug-in programs are available separately or in bundles. Bundles include a number of different DSP programs. ► The equalizer and the filter are examples of spectrum processors because they alter the spectral balance of a signal. The equalizer increases or decreases the level of a signal at a selected frequency by boost or cut (also known as peak and dip) and by shelving. The filter attenuates certain frequencies above, below, between, or at a preset point(s). ► Four types of equalizers are in general use: fixed-frequency, graphic, parametric, and paragraphic. Although not an equalizer per se, a so-called dynamic equalizer is a signal processing feature that affects frequency response through compression. ► The most common filters are high-pass (low-cut), low-pass (high-cut), band-pass, and notch. ► Psychoacoustic processors add clarity, definition, and overall presence to sound. ► Time processors affect the time relationships of signals. Reverberation and delay are two such effects. ► The four types of reverberation systems used for the most part today are digital, acoustic chamber, plate, and convolution; reverb plug-in software may be considered a fifth type. ► Digital reverb reproduces electronically the sound of different acoustic environments. ► The acoustic reverberation chamber is a natural and realistic type of simulated reverb because it works on acoustic sound in an acoustic environment with sound-reflective surfaces. ► The reverberation plate is a mechanical-electronic device consisting of a thin steel plate suspended under tension in an enclosed frame, a moving-coil driver, and a contact microphone(s). ► Convolution reverb is a sample-based process that multiplies the spectrums of two audio files. One file represents the acoustic signature of an acoustic space. It is called the impulse response (IR). The other file, or source, takes on the characteristics of the acoustic space when it is multiplied by the IR, so it has the quality of having been recorded in that space. ► An important feature of most digital reverb units is predelay—the amount of time between the onset of the direct sound and the appearance of the first reflections. ► Delay is the time interval between a sound or signal and its repetition. ► Delay effects, such as doubling, chorus, slap back echo, and prereverb delay, are usually produced electronically with a digital delay device. ► Flanging and phasing split a signal and slightly delay one part to create controlled phase cancellations that generate a pulsating sound. Flanging uses a time delay; phasing uses a phase shifter. ► Morphing is the continuous, seamless transformation of one effect (aural or visual) into another. ► A pitch shifter uses both compression and expansion to change the pitch of a signal or the running time of a program. ► Dynamic, or amplitude, processors affect a sound’s dynamic range. These effects include compression, limiting, de-essing, expanding, and noise gating. ► With compression, as the input level increases, the output level also increases but at a slower rate, reducing dynamic range. With limiting, the output level stays at or below a preset point regardless of its input level. With expansion, as the input level increases, the output level also increases but at a greater rate, increasing dynamic range. ► A broadband compressor acts on the dynamic range of the input signal across the entire frequency spectrum. A multiband, or split-band, compressor affects an input signal independently by splitting the audio into multiple bands, as needed, and then recombining the outputs of the bands into a single mono or stereo broadband signal. ► Compressors (as well as limiters, noise gates, and expanders) facilitate sidechaining—taking the input of one sound to manipulate another sound, usually by using one signal to control the level of another signal. One sound is lowered when the other sound gets loud. The term used to describe this action is ducking. ► A limiter is a compressor whose output level stays at or below a preset point regardless of the input level. It has a compression ratio between 10:1 and infinity; it puts a ceiling on the loudness of a sound at a preset level. ► A de-esser is basically a fast-acting compressor that acts on high-frequency sibilance by attenuating it. ► An expander, like a compressor, affects dynamic range. But whereas a compressor reduces it, an expander increases it. ► A noise gate is used primarily to reduce or eliminate unwanted low-level noise, such as ambience and leakage. It is also used creatively to produce dynamic special effects. ► Noise processors are designed to reduce or eliminate such noises as clicks, crackles, hum, and rumble from an audio signal. ► Multieffects signal processors combine several of the functions of individual signal processors in a single unit. ► A voice processor, also called a vocoder, can enhance, modify, pitch-correct, harmonize, and change completely the sound of a voice, even to the extent of gender. ► There are highly specialized plug-ins that add almost infinite flexibility to sound shaping. ► When selecting a plug-in, it is important to know whether it is compatible with a given digital audio workstation.