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Digital signal processor and multi-effects processor units. Features, functions, and explanations

Despite the ongoing debate as to whether recorded music should approximate the audio atmosphere of a live performance or not, some amount of signal processing is beneficial to any mix. Effects processors is a general term for many different types of equipment. Some correct the volume levels of the recording, others deal with the tone of the recording, and still others deal with the atmosphere in which the recording was made. Dynamics processors, also called compressors, fulfill the first function. Equalizers mold the timbre of the sound, while " effects processors" deal with the room ambience, reverberations and other special effects.

• Chorus = Echoes that are so close in time to the original sound that they give the feeling of more than one instrument playing. Chorus fattens any sound nicely, and is tempting to overuse.

• Compression = This reduces the range of volume variation. Sometimes a signal may have too wide a range of volume, for example a singer who screams and whispers. Compression makes the soft parts a little louder and the loud parts a little softer. Be careful with compression, because if used to intensely, it can create an unpleasant pulsating effect.

• Compression ratio = When a signal increases in volume above a certain threshold level, compression decreases the amount of that increase. The compression ratio tells us how much of the increase will get through. For example, if your compressor is set at a ratio of 4:1, and your signal increases by 8 dB, the compressor will output a signal that only increases by 2 dB. Other important factors are the speed with which the compressor kicks in and then releases the signal.

• Delay = The single echoes of the sound. Think of the guy in the desert yelling " hello" and hearing five hellos back and thinking there are five other people there in the desert with him.

• Effects returns = The control which brings the process signal back to the channel mixer. By varying the amount of signal processed, you can vary the feeling of the recording space. The more signal you process, the more the original recedes and the room takes over.

• Effects Sends = The control which sends the signal to the effects processor.

• Equalization = The function that boosts or lowers different frequencies in the sound. You can change the timbre of a sound by boosting higher frequencies, for example.

• Expansion = The opposite of compression, this expands the dynamic range of the signal. This can be useful in reducing noise from the background, as well as boosting a weaker signal.

• Flanger = A popular guitar effect. What this does is take the echo and combine it with itself. It's kind of like putting chorus on a delay, and creates a very fluid and spacey kind of feel.

• Graphic equalization = Graphic EQ has a fixed number of set frequencies that you can raise or lower. Thus it is less flexible.

• Limiting = A more brutal form of compression, this simply stops the sound from going above a certain volume level. It is used to prevent clipping and other distortion of high-volume sounds.

• Noise gate = A form of noise reduction that eliminates any signal that falls beneath a certain decibel level. It is very useful in reducing background sounds.

• Parametric equalization = Parametric EQ raises or lowers the volume of an adjustable frequency. They commonly come in three bands, meaning there are three choices of frequencies (within the low, mid and high range) that you can adjust.

• Pitch shifting = Changing the pitch of the recording. Digital technology allows us to do this without changing the speed of the recording.

• Reverb = The cumulative effect of the natural echoes of a room. When a sound is made in the room, there are many echoes bouncing off the walls in the ceiling that create a sense of the room size and building material. Reverb is the most commonly used the effect.

• Timeshifting = Changing the speed of the recording without changing the pitch. With tape, if you ran the tape faster, the pitch got higher. Speed it up too much, and you got Alvin in the Chipmunks. Slow it down too much, and you got Paul Robeson. With Digital, you can correct tempo errors without affecting the pitch.