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Want to add more punch to your recordings? Ian Waugh leads off with a quick guide to dynamics
Of all the effects available in modern sequencers, dynamics processing is one of the most useful. It not only can help balance tracks but it can be used creatively to make a recording sound bigger, more up-front, and to add punch to bass lines and drums.
There are several types of dynamics effect (we'll look at them in more detail in Part 2) but they are all based on the same process. Quite simply, they reduce (compress) or increase (expand) the dynamic range of a signal.
The dynamic range is the difference between the quietest and loudest parts of a signal. Compression reduces the range between the quietest and loudest sections, usually by reducing the louder parts. Expansion makes the quieter section more quiet still and the louder sections even louder.
Why...?
Why do we need dynamics effect? Let's say you're recording vocals. The human voice has a very large dynamic range and there could be sections where the voice is far too loud for the backing and other points where it's too quiet. If you run the vocals through a compressor, it will even out the volume making the quiet sections louder and the loud sections more quiet.
Similar compression techniques can be used with any sound or instrument with a large dynamic range which has to fit alongside sounds with a smaller dynamic range. This includes brass, some percussive sounds and sound effects.
Compression is also invariably used on the final mix to squeeze more sound or 'warmth' into a recording. It increases the apparent loudness of a recording.
Compression is used a lot in radio broadcasting. Listen to a piece of classical music which has a much larger dynamic range than pop music on the radio and then play the CD. You'll soon notice the difference.
How it works
Dynamics effects work by monitoring the level of a signal and adjusting it when it reaches a certain level. Some effects show the changes on a grid which makes it very easy to see exactly how the sound is being changed. Others simply have a LED meter showing the level of compression taking place.
The average dynamics processor has four main parameters:
Threshold
This is the point at which the effect kicks in. In the illustration below, the threshold is set to -24dB but as no effect is being applied there is no change in the output. (For more information about dB - decibels - and their use in recording click here )
Ratio
This determines the amount by which the incoming signal is reduced. The illustration below shows a 2:1 compression ratio which means that for every 2dB increase in the incoming volume level, the output level is only increased by 1dB. The Threshold is set to -48dB and you can see that the incoming level at -24dB, for example, is output at -36dB.
The example below shows a ratio of 4:1.
The final example shows a ratio of infinity:1 - no matter how loud the incoming signal rises above the threshold, it will never get any louder than -48dB. This type of compression is used in Limiters (coming up in Part 2).
Attack time
This is how long it takes the compressor to react to the incoming signal once it has reached the threshold level. With a fast attack time, the effect will kick in straight away but this may not always be desirable. Consider a percussive sound such as a guitar or xylophone. If the attack is fast, it will reduce the initial transient of the sound creating a dull or muddy effect. By increasing the attack time, the percussive transient passes through the effect before compression begins, retaining the percussive effect and, in some cases, accenting it. This can be useful for adding punch to drum sounds.
Release time
This determines how quickly the effect relinquishes control over the signal when it drops below the threshold. A fast release could cause the sound to swell up in volume very quickly and create an effect called pumping or breathing. It's a little like someone moving a volume fader up and down very quickly. If the release time is too slow, the system may not react to subsequent volume changes and keep the level compressed when it ought not to be.
Gain controls
Most dynamics processors also have a gain control. Because compression, by its nature, reduces the volume of a signal, you will generally need to increase it after compression.
Some effects, such as Sound Forge, have an Auto Gain Compensate function which applies gain during processing in an attempt to keep the maximum input and output levels constant.
In the next part we'll look at some popular dynamics effects and when to use them.
