Blog

“Audio Compressor” (Fine Tuning)

 A Review By: Alphonso Soosay

audio-compressorsThis practical review about Audio Compressor provides the ‘combination’ to unlock the full potential of your creative audio recording compressor use. The useful issue to know about audio compressor is that it is one of the most used audio processing units in every recording studio and TV broadcast studios in the world, but it is often misunderstood and it can be tricky at the first read to get a grasp of what it actually does. The other essential feature to know is that, audio compressor compresses the sound, not the quality, but the dynamics of the sound. It cuts down the unwanted peaks on the track so that you can increase the overall volume to your reference standard level.

When you first use an audio Compressor, you might be thinking what can a compressor do for your music? Satisfactorily it can be used on different tracks while recording and in your final mix, as well as on the master output channel. It is most often used to get a more consistent level of your source, but sometimes it can be used for creative purposes. One example of this is the “pump effect” on Rap music, which has become very popular in house music for the many years. However, for the majority individual users, the compressor is used to increase the volume by decreasing the dynamics.

I will explain in plain words what the most common four controls (Threshold / Ratio / Attack & Release) of a compressor can do in audio recording situations:

1. Threshold: This is where you set the level on which the compressor should start working. 0db is absolute max level audio-compressorand you will probably set the compressor to something like -20db. This means that whenever the signal reaches above -20db the compressor will come in and decrease the dynamics of the levels going above the threshold. The right setting will see the dynamic movement coming to rest at special moments otherwise you get a flatter more lifeless sound. Having uncompressed sound emerging from the processor at appropriate musical moments adds colour and contrast to the sound. For example, permitting the dynamic movement to come to rest in some quieter moments allows that moment to attain a momentary, bigger, 1:1 presence, and prevents it from rushing towards the listener with unwanted noise. It’s sad enough that the little quiet moments are small without being squashed smaller still due to high compression ratios. Each time the sound comes up for air, so to speak, it attains a sense of reality, a 1:1 ratio.

2. Ratio: This is how much the dynamics above the threshold will decrease in a factor of x to 1. 2:1 means that the dynamics will be halved. At this point, set the Ratio to its maximum, so it’s going to sound over compressed and you will hear it. So the next step is to adjust the Ratio lower, as much as you can without losing the effects you previously created.   Think of the Ratio control a bit like a telephoto lens, the higher the Ratio, the smaller the sound is although it will be more controlled. The lower the Ratio as in 2:1 (given the same output voltage), aesthetically feels like a larger image.
So the lower the Ratio the bigger it is, but at the risk of getting out of control. Meanwhile, the higher the Ratio, the smaller it is although it’s more contained. The idea here is usually to try and make your instrument or mix sound big, but in control. So, bring down the Ratio, and then when you don’t really hear the effects that you like the thickness of the source,     you can raise the Ratio a slowly and at the same time focussing on width. At this stage, don’t think about the Attack or the Release and, for that substance, don’t think about Ratio in terms of numbers just think about the width and firmness of the sound. Well, as you raise the Ratio, the sound will become firmer (and smaller) and as you lower the Ratio it becomes softer (but bigger). So you might want to think along the lines of How firm do you want this’ Musical Instrument to sound, versus on the Final Mix.

3. Attack: This is the amount of milliseconds before the compressor starts after the threshold has been reached. The first thing you do is set the 1) Ratio to as high as it’ll go 20:1, infinity, the highest you’ve got. Subsequently set the Release time to as fast as it will go, which admittedly is faster than you did ever want it. Then, drive the audio into the unit, either by lowering the Threshold or increasing the Input depends on the unit, and listen while you adjust only the Attack time. Listen to the Attack the leading edge of the sound while moving the Attack knob. Try to ignore the horrible pumping caused by the after effects of the fast Release just listen to the Attack. (The ultra-fast Release lets you hear far more individual attacks than a slow setting.) Listen to the front edge of the sound. Notice how the Attack knob affects the size of the strike. So, if it’s a snare drum that you are compressing, and the Attack is on a fast setting, it’s sounds as though the Drum stick is really skinny; then while if the Attack is on a slow setting, it sounds as if the stick is much thicker. Likewise, if it’s an acoustic guitar and the Attack is on a fast setting, you are just hearing the finger nail come through as it hits the string; while if the Attack is slow, you might get the whole strumming effect  through, the entire transient by-passes the compressor. So, forget all the after effects, just listen to the thickness of the Attack until it’s ‘full of flavour’ you might want it thin, you might want it thick, just think creative. And then, because the ratio is so high and the release is so fast, you will be able to hear the affect of the Attack time much clearer than if they were on any other setting. This technique effectively turns your ears up to heighten your perception of the Attack time control.

4. Release: This is the amount of milliseconds before the compressor ends compressing the sound after the signal has dropped below the threshold. This is the stage to play with the Release time. ‘Release’ controls the speed at which the compressors for audio recordingsound glides back at you after being punched away. The trick is to get that speed to become a musical component of the sound. You might ask, ‘Do you mean in time with the music?’ or ‘With fast music do I set it faster than I would for a slow ballad? Perhaps, but certainly don’t think, ‘I only want it fast because I want to compress the crap out of this’ don’t ever think or do that. In fact, make it as slow as you can, so that the compression envelope ‘bounces back’ to reinforce or establish the groove of the music. Remember, any dynamic movement in a song affects the groove, and compressor/limiters are no exception. It doesn’t matter if the singer is moving back and forth of their microphone, or you are frantically wiggling a fader, or a compressor is pushing and pulling on a sound, the groove is at risk of being enhanced or destroyed by dynamic movement. So, do not set your Release to a fast setting just because you want to hear something buried behind the sound. Just overlook that. There are bigger fish to fry. You are already compressing a little bit, so these background sounds will come forward anyway. Instead, you want to think, ‘How slow can I get it while maintain some control? Because the power in the groove is really a slower-moving, subliminal yet powerful wave, it’s not an ultra-fast thing that’s there to crunch your sound. Even in a frantically fast-paced melody, a slower, subconscious under-current carries most of the power. For example, you might have it so slow that by the time the next strike of the snare drum comes along it’s not quite fully released. But that’s all right. A arranged approach might intellectually tell you that it has to be fully released before the next strike Listen to the Release very carefully. Feel the way it glides or bounces back at you and there will be a point where you sense that this bounce-back is kind of like a swing, almost like someone swinging from a rope in a tyre in groove with the tune. It doesn’t have to be absolutely in time, as anyone who teaches music will tell you, keep in time, but should not necessarily play the time. So, don’t just make it a quarter of a beat or whatever, just look for that groove, and that’s your release time. Make the colour of the Release a musical component that pushes you into the next beat without pre-empting the beat. Let the drummer strike you while the pressure is still rising instead of letting the compressor finish its swing dead air limp moment. If it does not sound correct. Allow the compressor to push the sound towards you until the music makes its next statement. Did you get the idea?  I must add that if you aim to make the product likeable (full of soul & extremely groovy; for example), the wrist of the listener will always turn up the volume for you more effectively than any compression ever could do.

I suggest that you take some time and experiment with a compressor in your recording studio or software version, an excellent example will be working it on an Acoustic Drums, Piano, Acoustic Bass or Acoustic guitar as you will hear the differences instantly.

In the past I have received emails from home studio operators local & overseas asking for help on how to use the audio Compressor correctly. The following are some of the letters and it reads like this.

Carlos Jackson is my name and I work with a 16 input Sound craft Recording Mixer. Having used the audio compressor for Vocals, Electric Guitars and Bass Guitars, for the last 8 years and I am never satisfied with the end result of the Mix. It’s either pumping too hard or the final mix sounds dead. How can I solve these problems?
I am a desperate man and I have an embarrassingly fundamental problem. I have been doing good work for years but even after all this time I am still unable to use the Attack and Release times with audio compressors correctly. I guess and listen and pray. What else can I do?

Another one from Michael Santos.
I know I am not alone in this because when I recently had a client’s product mastered, the mastering engineer whom I work with also could not get it right either. He set his compressor’s release incorrectly. Needless to say the audio pumped like crazy and I cannot listen to it now.

One from Richard Piper
Knowing that I am at least aware of what Attack and Release times are, my question is how do I marry them to the input signal that the processor is supposed to be processing? Examples of musical instruments used are, Snare drum, Guitars, Vocals, Brass Instruments & difficult Bass players.
Where I am lost is the ‘theory of its use’.

Would you know the ‘Trick’ and how?

And another one from Carlos Santa Maria
I have got hold of 10 hardware compressors in my home studio, with many musical instruments and Microphones, & I am tired of guessing on how to use it correctly.

Note: it is difficult to explain on the telephone or email because one has to listen to the output source to tell what changes has been made to the input source.

I know exactly how these musician feels. I spent years trying to hear the difference between the range of Attack times, Ratio, and Release times, wondering what I should be thinking about while fiddling with these four controls. The task of compressing went from being a confusing scary one to the most fun and creative fiddling with compressors knobs in the recording studio. Your “Ears” are like the “Referee” and you have to make that final Judgement after knowing what to do.

Audio Compression is like cracking a Safe. Compressors have four basic knobs (parameters) and the key to classy compression is as simple as the order in which you reach out and focus on adjusting those knobs. As soon as you get the sequence right, you will hear more clearly the effect of each parameter thereby arriving at a truer and more musical setting. The compressor combination lock has four basic knobs. Adjusting them in a special order also prevents you from returning to a previously adjusted control. Don’t you hate it when you’re happy with the Release time until you fiddle with the Attack? They do affect each other when adjusted randomly or out-of-sequence. Chasing your tail is about to become a thing of the past. Like cracking any combination lock, once a knob falls into place, you need not revisit it. Each step represents decisive progress. If you follow these guided steps, you will have a big and bouncy, firm and flexible, juicy, funky and slippery groovy sound or whatever you like. Or as some people would say on the final mix, ‘wow the music is much tighter and has a more detailed sound’.

It does not matter if you are compressing an individual Voice, Guitars, Bass, Acoustic-Drum, Saxophone, or compressing an entire Final Mix, these steps will get you there quickly and decisively by taking out the guesswork, training your ears what to listen for. It’s rather like growing bigger ears (because you hear the effects more clearly) and a larger brain (because confusion is replaced with clarity of thought). In simple principle, just think, (ARRT) Attack. Release. Ratio. Threshold. Give it a shot and have fun with balanced big sound. Looks like you will also make it sound as how you would fancy it. Have fun with the use of the audio Compressor for a more natural sound.
Alphonso Soosay.
Audio Recording Engineer / Musician
 

More
Its all about the Music Follow on Twitter Facebook google plus LinkedIn