DYNAMIC PROCESSORS

Some types of sound source such as certain instruments, by virtue of their construction or performance characteristics and human voices, are capable of producing a wide range of dynamics – for both very loud and soft sounds. During a recording session, the risk of unpredictable peaks when the signal is too loud or too quiet is an important factor.
Dynamic processors can greatly enhance the quality of mixes and songs. They manage these elements within fixed parameters so that they can be controlled within the mix. They act like automatic faders, riding the signal and either evening out unwanted peaks or remove some sounds entirely. They directly relate to a signal’s perceived or relative loudness in the mix.
Compressors: They work by proportionately reducing a signal’s peak volume when it exceeds a maximum level set by the user while leaving anything below that maximum level untouched. They reduce a signal’s overall dynamic range by making the loudest peaks quieter. Typical controls of a compressor and the wider family of dynamic effects are:

• Threshold: The user-definable peak level above which the compressor begins to reduce the volume of the signal. In digital systems, the maximum threshold will usually be 0dB. The point at which the processor kicks in is known as the “Knee”. In some systems, the knee can be set on a scale between “Hard” and “Soft”, so the compression either kicks in swiftly (a hard knee) or more subtly (a soft knee) when the threshold is exceeded.
• Ratio: The amount of volume reduction that occurs above the threshold expressed as a ratio- such as 2:1, 4:1 and so on.
• Attack: The speed, measured in milli-seconds at which the compressor reduces the volume of the signal when it has exceeded the threshold.
• Release: The speed at which the compressor cuts-off and restores the original input level of the signal.
• Input Gain: The amount of unprocessed signal sent to the compressor
• Output Gain: The amount of compressed signal sent to the output multipressors:
  Some software suites provide Mutband Compressors (Multipressors), which are compressors that are programmable to work aross a user-definable frequency range, or group of frequency ranges. This means that a compression threshold can be set to be solely applied or predominantly to signals within a specific band.
• Limiters: A limiter is essentially a more extreme compressor, setting a hard threshold through which a signal’s volume is not allowed to pass. Limiters are not able to respond instantly and in order to prevent very rapid peaks getting past the limiter, most limiters have a Look Ahead control that sees the peak coming- in reality, by putting a tiny delay of about 1ms into the signal path to allow it the time to react.
• Expanders: They provide the opposite function of compressors by increasing a signal’s dynamic range either above or below a set threshold but with similar editable parameters.
• Noise Gates: These are expanders that allow signal levels above a user definable threshold to pass without any processing, while completely reducing signals that fall beneath that threshold. They remove unwanted noise. (Middleton, 2006)

2. DYAMIC PROCESSORS IN RECORDING STUDIO

Some of the various dynamic processors that are available include:

• 1) Compressors in Reason
• 2) Choosing Compressor presets in Apple Logic
• 3) Logic
• 4) Expander preset in Logic
• 5) Noise Reducer in Goldwave
• 6) Soft Limiter in Logic
• 7) The Dolby SR noise reduction unit which is used to reduce the background hiss on tape recordings (Middleton, 2006)

3. FUNCTIONS OF NOISE GATE

Removal of Background Noise: A noise gate is a processor that is either on or off; that is, it either lets the signal through or it does not. It is a useful tool, particularly when recording live instruments with a microphone. The microphone will pick up any background noise that is floating around in the studio such as the buzz of a guitar amplifier, a constant drone of a computer fan and feedback noise. It will even pick up the noise in the analogue circuitry of the microphone pre-amplifier. Placing a gate into this signal chain will silence the channel while the instrument is not playing and open it when the instrument is played and the threshold exceeded. Gates can be used to create rhythmic effects by feeding separate signals to the gate’s input and side-chain input. Some noise gates allow to adjust the tone of the side-chain signal (that is, the portion of the signal that the noise gate “listens to” to determine whether to open or not); this makes the gate more sensitive to the low- or high-frequency components of the signal being processed. It is also common for a noise gate to have a hold time control. This keeps the gate open for the selected amount of time after the signal falls below the threshold level, and helps to ensure that the decay portion of the sound being processed is not cut-off. Some of them even work by turning down the signal rather than cutting it off entirely. (MacDonald, 2004).

4. THE USE OF COMPRESSORS IN MIXING

At the tracking stage the most basic use of a compressor is to function as an automatic volume control, reducing the fluctuations in level that are common when recording live instruments. For example, when a singer is moving around slightly, or an open chord on an acoustic guitar tending to be louder than a fretted one. In a digital recording system, there is a maximum signal level that can be recorded before the clipping occurs. This is referred to as zero decibels full scale (0 dBFS).
It is the peak volume level of a signal that determines how much gain can be applied before this 0 dBFS point is exceeded. Unfortunately, our ears are not very sensitive to the short, loud transients (such as drum beats) that create signal peaks, and it is actually the average signal level that our ears use to give us the impression of loudness or lack of it. Reducing the level of a signal’s peaks allows you to apply more gain to the signal as a whole without causing clipping, and this in turn results in a higher average signal level, making it sound subjectively louder. (MacDonald, 2004)