Chapter 2: What Is A Compressor?
The level of a vocal may vary widely. As shown in the typical example in Figure 1 “Compression - signal level graphs”, the unprocessed signal has a large dynamic range between the highest and lowest levels. Applying compression reduces the highest levels, thus reducing the dynamic range, while leaving the signal below threshold relatively unaltered. Because the peak level of the signal is now lower, make up gain is added to restore the original peak level. The result is a much more controlled and usable sound.
Uses of compression
Compressors were originally devised to reduce the dynamic range of audio signals. To do this they use a gain cell that makes adjustments to signal levels automatically, dependent on the level and dynamic of the signal itself, and depending on the character and control settings of the particular compressor unit.
Over the years many different brands of compressor have been produced using many different types of gain cell technology, each with a distinctive sound. Users have found applications that suit many of these, taking the use of compressors far beyond simple dynamic range reduction and sometimes even generating the complete reverse — dynamic enhancement. Typical applications include:
•Protecting systems from amplitude overload.
•Improving the power of signals when an artiste’s performance is inconsistent.
•Maintaining a stable signal level to help an instrument sit better within a mix.
•Changing the percussive timbre of an instrument to produce more punch.
•Compressing a mix so that it maintains a stable signal level, typically trying to make it sound louder.
•Changing the percussive timbre of a mix to make it sound more whole and add punch.
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Unwanted side effects
Very often the process of compression produces unwanted side effects, especially if the chosen compressor does not match the application it is being put to very well. These can include:
•Breathing — when high frequency environmental or processing noise levels jump up and down, sounding similar to someone breathing in the background.
•Pumping — when level modulation can be heard on an instrument, making it sound unnatural.
•Amplitude flutter — a faster oscillating modulation that makes sounds gritty.
•Source
•Transient enhancement — unwanted accentuation clicks at the start of a sound.
•Dull sound — when all the natural attack and brilliance is stripped away from the sound source.
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6 | Operator Manual |