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Dynamics Tutorial - From Focusrite

Published: Fri August 13, 2004  News Feed

How often have you been watching TV and noticed that the adverts seem to be much louder than the program you\'re watching, even though you haven\'t touched the volume control? It\'s all down to the clever use of dynamics by advertising companies, because they know that the louder something is, the more likely it is to grab your attention. It\'s the same with music: if one track appears louder than another, it\'ll grab the listener\'s attention more. Dynamics processors play a huge part in this, making music appear louder, more \'in ya face\', and generally much more appealing to an audience.

Dynamics processors take in a range of machines, including compressors, noise gates, Finalizers and de-essers, so let’s have a look at what each can do for your music.

Dynamic go-getters

The most important processor to have around for increasing the loudness of a mix is a good compressor. This is designed to limit the dynamic range of a track, allowing you to turn the overall volume of a mix up louder before finally mastering it to CD. The best way of explaining how compression works is to give an example, so let\'s say you\'ve just mixed a track involving drums, bass, lead guitar, vocals and a synth playing a chord over the top.

Obviously you\'ll need to record it at the highest possible volume, but when you turn the volume of your mix up, in certain places throughout the track the vocals, guitar or chord parts can push the signal indicators into the red, which results in the sound distorting, so you have to turn the volume of the mix down to prevent it. Of course, you could always drop the volume of the offending instrument or vocal, but if you do, it could sound too quiet in the parts of the track where it wasn\'t clipping. In the old days before all this newfangled technology was available, the only way to counteract this was by employing an engineer with lightning reflexes and a good ear who listened for the peaks in a track and dropped the fader at the offending part before pushing it up again for the rest of the mix - essentially a forerunner to mix automation.

Things were certainly made easier by the introduction of compressors, simply because they allow you to set a volume threshold to control when the compression kicks in. In our example this would be set just below the offending part\'s peak. If the offending signal tries to go into the red during playback, the compressor immediately reduces the signal, preventing the sound from distorting and allowing you to push the overall volume of the track up more, making your mix louder and more impressive.

However, as tempting as it may be to keep compressing and pushing the volume up louder and louder, there are limits. Too much compression can force your mix to lose its dynamic edge, resulting in a rather flat sound. So it\'s a case of compressing as hard as you can while also listening out for the dynamic range of your mix, and getting the right balance between these two considerations.

Taking Control

Looking at the controls on a compressor, you\'ll notice that there are probably several others in addition to a threshold dial. They also include ratio, attack, release, gain and sometimes a setting for hard or soft knee.

The ratio is the amount of compression applied to a signal when it exceeds the threshold you\'ve set. This is listed, not surprisingly, in values such as 2:1, 4:1, 6:1 and so on. So, for example, a ratio of 2:1 would compress the output signal to half that of the incoming signal, and the higher the ratio, the more the level is reduced once it exceeds the threshold.

The attack and release (the latter sometimes known as \'decay\' on compressors) are exactly the same as they are with a synth envelope, controlling how the compressor will behave when a signal exceeds the threshold. Attack defines how quickly the compression starts, and release controls at what stage compression stops after the signal level is lower than the threshold again; a long or slow attack will not activate the compression until the signal’s level has been over the threshold for that length of time, whilst a slow release will mean that the compressor returns to its resting position fairly quickly. Obviously, this also has limitations and should be set carefully depending on what signal you\'re compressing. Using a long attack on a kick drum will have no effect at all, as the signal only exceeds the threshold for a short amount of time and normally decays fairly rapidly. Also, if you set a fast attack time but a slow release on a kick drum accompanying some other lower level tracks, the compression (triggered by the kick) would be held for too long and so would audibly punch holes in the signal.

While using the envelopes, you may also need to take the knee setting (if offered) into account. This can be considered as the shape of the compression curve between the compressed and uncompressed signal (either side of the threshold). A hard knee results in more aggressive and sudden compression, whereas a soft knee creates a smoother or more transparent transition from uncompressed to compressed.

So, if you\'ve set the threshold, ratio, attack and decay correctly, the compressor should compress effectively and reduce the dynamics in a sound, but you also need to compensate for the overall reduction in volume of the signal. This is where the gain control comes in: you can use this to bring the signal back up to its original level (minus the peaks that have been compressed, of course).

When finalising a track prior to burning it to CD, it\'s usual to compress the whole mix, helping you to increase the volume even further, and this is when the most common mistakes are made. The threshold has to be set very carefully; if it\'s set to react to the kick drum, for example, it will compress/uncompress on every hit, resulting in a mix that pumps and \'breathes\', rising and falling in loudness.

There are no rules as to what settings to use on a compressor, so it\'s only possible to offer guidelines (see p51). In the end it will depend on your ears and the mix you\'re working with. Apart from reducing the dynamic range of an instrument, compressors can also be used in a creative context, as any dance musician will tell you. Drums in dance music, particularly the kick and snare, are very heavily compressed; so much so that you can actually hear the loss of dynamics in the sound. The main reason many dance tracks have such a huge beat is that massive compression has been applied. As we mentioned at the beginning, however, there\'s more to dynamics than just compressors...

Close the gate

Noise gates can be just as important as compressors in creating a powerful mix. When recording a guitar or vocals - in fact, anything using a microphone - unless you\'re in a professionally sound-treated room, you\'re guaranteed to capture some background noise. While the vocalist is singing or the guitarist is playing his piece it isn\'t as obvious, as the sound being recorded is louder than the background noise; but when they come to rest, the noise will become more prominent.

Noise gates work much like compressors, except in reverse: any sounds that exceed a threshold setting are let through unprocessed, while sounds below are simply cut off altogether, resulting in total silence. As with compressors, they also feature attack and decay settings that react as you would expect. Using a fast attack will result in the sound being cut immediately, while a slower setting would slowly gate the signal. A typical noise gate will also feature a couple of extra controls: hold and range. Hold controls how long the gate will be open or how long the level below the threshold is cut/reduced, while range adjusts the amount of signal that can be heard while the gate is closed or how much the signal below the threshold is reduced by.

To better explain the range control on a noise gate, let\'s introduce the extra input that some gates (and compressors) feature: the sidechain. A signal, usually from a microphone, is connected to the sidechain, and instead of the threshold functioning as normal, the sidechain takes control of it. As you speak, the noise gate drops anything else playing through it that’s below the threshold to the volume or \"range\", set by the range control. It\'s the same with a compressor; as you speak (or sing), the \'background\' music going through the main inputs and outputs of the unit will be compressed to the level determined by the ratio control.

There are plenty of uses for a sidechain with both compressors and noise gates. With compressors, the most common use is to \'duck\' instruments to make room for vocals. For example, a guitar can swamp the bandwidth that it shares with the vocals in a mix, so by sidechaining the vocals into a compressor that has a guitar signal as the input, when the vocalist sings, the guitars get compressed, allowing the vocals to sit in the mix better. Noise gates are popular with DJs, as by sidechaining their voice and setting a low range, when they speak, the music drops in level, allowing you to hear them more clearly.

Get creative

As with every other processor and effect in today\'s studios, compressors and noise gates have been used and abused way beyond what they were originally designed to do. The most memorable use of a noise gate in recent years was on Olive\'s You\'re Not Alone, but it\'s a trick that\'s been employed again and again - even Blondie found a use for it (the pad in Heart of Glass). This sort of sound is achieved by feeding a simple hi-hat pattern into the sidechain input of a noise gate, then playing a chorded pad or string sound through the same gate, so that every hi-hat hit closes and opens the gate, causing a stuttering effect on the pad.

Another trick is to put plenty of reverb on a kick drum and then set the noise gate to cut off the reverb\'s tail, giving a louder and more prominent kick. There\'s more to dynamic processors than just noise gates and compressors though; there are also de-essers and finalizers.

De-essers can be employed on vocals to reduce sibilance. This is an effect caused by a singer over-stressing the \'t\' and \'s’ sounds, resulting in the recorded vocals sounding like a dripping tap, a steam engine or, in the worst cases, both. Now, while most vocalists shouldn\'t need any specific treatment - and it\'s always best to avoid applying any if possible - using a bright capacitor mic, adding compression or processing with a bright reverb will bring up the levels of sibilance, which is where the de-esser comes in. They work by literally targeting a narrow frequency band, just the ‘s’ or ‘t’, and compressing it. These devices are designed to reduce the effect of the over-stressed \'s\' and \'t\', although if at all possible it\'s best to try and capture the performance right in the first place, as de-essing can have a detrimental effect on vocals, robbing them of their live feel.

Finalizers are used to sprinkle a little of that oft-mentioned \'fairy dust\' over a track. When you\'ve finished mixing a piece of music, sometimes it can still sound a bit plain, so feeding it into a finalizer can add an extra sparkle gained from boosting the lower and upper harmonics, along with adding small amounts of reverb to brighten up the image. Appealing as this may sound, many engineers and producers avoid finalizers like the plague, as they can add too much polish at the expense of the energy and ‘grittiness’ that you might have originally wanted, resulting in an over-produced sound. There\'s also the problem of users attempting to use them to make a bad mix sound better, which simply doesn\'t work. Instead, it merely emphasises the worst parts.

So, now we have reached a good point from which you can begin using dynamics processors to liven up your mix and make it louder, but it\'s important to remember that there are no hard and fast rules. It\'s down to your own ears and, as with any effects processors, compressors, gates and their ilk, definitely worth experimenting with as wildly as possible to come up with new sounds of your own.

 

Attack

Release

Threshold (dBu)

Ratio

Knee

Full track

Fastest possible

Fastest possible or Auto

-5 to -9

2:1 to 3:1

Soft

Drums

5ms

5ms

-15

5:1 to 8:1

Hard

Synth Bass

4ms to 10ms

10ms

-4 to -8

4:1

Hard

Real Bass

4ms to 10ms

10ms

-2 to -10

8:1

Hard

Vocals

Fastest Possible

Slowest possible or Auto

-3 to –8

4:1 to 12:1

Soft

Brass

Fastest possible

Fastest possible or Auto

-10 to -14

2:1 to 8:1

Hard or soft

Guitars

Fastest Possible

Fastest possible or Auto

-10 to -14

8:1 to 14:1

Hard or soft

All these values are meant as a rough guide, the exact levels of threshold and ratio are very much dependant on the signal being compressed, not to mention the character of the sound you want to create. This threshold guide could also be misleading in certain situations where a different scale is provided; on the VoiceMaster Pro for example, a dBFS scale is provided so a conversion will be necessary (assume 0dBFS to be around 20dBu, so –5dBu to be around –25dBFS). Perhaps you could begin with these settings and play around with one parameter at a time to decide what gets the best audible results.

On the other hand, if you want to set up the compressor without the use of the table, then once you\'ve got your sound fed into a compressor, the first control you need to adjust is the threshold, as this sets when the compressor will start to ‘squash’ the signal. In most cases you adjust the threshold so the compressor works on the loudest parts of your signal. Next, you need to set the ratio. This setting will depend entirely on how you want your music to sound, so if you\'re writing dance music, you should set a fairly high compression ratio. Set the attack and release according to the nature of the waveform, if there are lots of transients (fast peaks) or not and whether they want to be compressed or left alone (read the earlier passages in this dynamics tutorial for more on attack and release times). Compressing a signal will lower its output volume, so once you have compressed the signal sufficiently, you\'ll need to raise the volume from the compressor and not from the desk, as this can unbalance a mix.


 

 
 
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