Origins

(this could take several articles, but let’s get slim on the facts and skip but the relevant ones, to avoid you catching some z’s while trying to read this).

Compressors appear in radio from the necessity to solve the problem of sound sources of different levels, preventing the transmitters overload and blow. Before that, the only solution was the radio engineer riding the fader down on loud parts and push it up on soft ones. As you may guess, unless those guys were fast as “Lucky Luke” their success was nothing but short. They need a device that had a peak control to protect the transmitter, (AM at the time) while balancing different material to be broadcast at consistent levels. Those have been called at the time, leveling amplifiers or limiters, but act pretty much like our days compressors. True limiting took “some” years to became as we know it today, with the help of better technology.

The first dynamic compressor made it’s appearance on the public address system at the 1936 Olympics, it was a Telefunken U3.

Studio engineers also adopt compressors to help them in the gain riding of live performances, to avoid distortion when they cut to disk, prevent tapes from over saturation and in digital to get rid of clipping.

Over the years these outboard units improved greatly and still are in use today (for those who can afford the luxury of having vintage compressors racks) from top studios, producers and mastering facilities. Later some mixing consoles manufacturers incorporate compressors in they channel strip desks. Today, in our DAWs, we abuse the use of plug-ins and in this particular case compressors as Seinfeld says because we can !!!

Do we know how to set it correctly or do we slap it on track and go wow cool, it’s loud now.

Let’s find out, first will have a look at the some of the ways used to get compression.

Dynamic controllers

Dynamic controllers modify the dynamic range of a signal

Dynamic Controllers Graphics

Compression

Compressors reduces the dynamic range of a signal, boosting the quieter signals and attenuating the louder ones, making the difference between loudest and softest sounds shorter by “squashing” it.

Threshold: this setting dictates (generally in dB) the level at the compressor kicks in, how loud the signal as to be before gain reduction begins.

Low values will compress most of the signal, with higher values only the peaks (highest levels of the signal) will be compressed letting signals below the threshold unaffected (with hard knee).

(There are some compressors that don’t have a dedicated threshold control /slider, these are fixed threshold units. In this case it’s the input knob that rules, the higher the input the more it overshoots the fixed threshold).

0 dB (calibrated mark) is the highest signal level you can reach in digital before clipping, a threshold setting of – 8 dB tells the compressor to kick in 8 dB bellow 0 dB.

Ratio: controls the amount of compression applied between input and output signals above the threshold.

A 1:1 ratio means no compression is applied, but a 2:1 ratio means that any input signal that overshoots the threshold say 6 dB will leave the compressor with a 3 dB reduction.

( - 6 dB threshold, ratio 2:1, signal leaves at – 9dB a 3 dB reduction above threshold)

Most compressors ranging from 2:1 to 20:1, at this ratio, is considered a Limiter (actually since a 10:1 ratio is Limiting).

Attack: controls the time the compressor takes to react to signals above the threshold (in milliseconds). With (lower value numbers) fast attack times, the signal will be attenuated almost immediately. With medium to fast attack times, it lets the initial peaks pass before the compressor kicks in (this can add a punchier sound with percussive effect). With a slower attack, it lets a sustained note passing thru before the compressor reacts.

Release: controls the time the compressor takes to react to signals bellow the threshold and stop compressing (also in milliseconds). The lower the number, the faster the release time. With very fast release times the compressor stops working immediately as soon it falls bellow the threshold (in most cases, this can sound unnatural). With too slow release times, the compressor may attenuate a soft passage followed by a loud one, simply because the unit had no time to recover.

(some compressors have switchable auto attack or auto release buttons, when those are engaged the fixed values stop being constant and will change automatically according to the level of the input signal).

Hard or Soft knee: Some compressors have the option between hard or soft knee. With hard knee the compression kicks instantly when the threshold overshoots. With soft knee, compression is obtained gradually (curve shape rather than hard angled) on both sides of the threshold, thus more gently and more transparent, hard knee has more compression effect.

 Hard knee  and  Soft knee

Make-up gain: automatic compensates the gain loss in compression relative to the threshold, ratio and attack settings.

Gain reduction meter: displays the amount of compression applied to the signal (in dB). Showing when gain reduction occurs, when it starts and when it stops, a good visual indicator to better adjust helper for attack and release settings. Some compressors have LED bargraph others have needle type meters. Bargraph is quicker to respond, thus more accurate.

Output: self explanatory, allows you to attenuate or boost the compressor output signal.

Side chain: allows the amount of compression be triggered by an external signal fed via an auxiliary output to the unit side chain input. For example to reduce sibilance (in conjunction with EQ) and duking, to name but two.

Stereo linking switch: a stereo compressor is basically a unit with two mono compressors working independently (dual mono mode). This switch allows both compressors to work as two identical ones preventing image shifting.

Today we have the fortune to incorporate most of hardware compression units emulated in our Daws like this Logic plugin.

With third party top plugins those emulations are becoming even better with every new version. Like Waves, Universal Audio, Sonnox, to name just a few excellent ones.

Stay tuned for the following part on compressors operational and other dynamic controllers tips.

This is a brief introduction on a series, “Mixing / Mastering”. I’ll be sharing my visions so you can feel more confident improving your mixes and go deeper on your knowledge of the subject along the way.

Mixing may seem an overwhelming task (and it is an art form by itself) but it doesnʼt mean that you cannot learn a few principles along this series to get you confident in trying it yourself and practice on your own compositions. The same applies to a musician or a composer, itʼs great to have a degree, but in case you donʼt, youʼll still be able to compose or play and get better at it. Learn to use the tools needed for the job and tune you ears into it. I hope youʼll take great benefit from the articles and they may give you extra finesse to your mixes.

In the mix youʼll have to recreate a sonorous stage, leveling the volume of the instruments, position in stereo field and give them depth.

Mixing became a necessity when multitrack recorders made itʼs appearance on the second half of the twentieth century, allowing several tracks to be recorded at once or overdubbed. Then a mixing board was needed not only to track them ( ins and outs ) to the multitrack recorder but also to level whatʼs on tape to produce a master.

You have to be familiar with the routing of the signals both on a physical mixer or the one you have “in the box” (the DAW mixer) hence the need to understand the channel strip. It may seem daunting when you first look at the mixer and see all those channels, have you ever thought “Iʼll never get that in my head”… well, that might be a little simpler than you think, forget “all those channels” for now, as the system itʼs modular, you have to learn only one channel as itʼs the same for every other track channels.

In ours DAWs the mixer may be presented in a different order depending on the one you have, ins, outs, aux sends, eq, knobs, solo & mute buttons and faders.

Working inside the DAW you can benefit of record and recall all your moves from automation parameters, such volume, pan, effects, plug-ins and midi control data.

Hereʼs a couple of tips on the listening environment and gain staging:

Monitors are very important, get the best your budget allows, remember that a $2 computer speaker wonʼt translate your mix, go for near field monitors, that allows you to work and mix at a close distance, youʼll find plenty on the market. Position them at your ears level, rotate the monitors towards you making a (60º degree angle) an equilateral triangle.

Since the majority of our home studios doesn’t have proper isolation, mixing at low levels not only avoids too much room reflexions added to the direct sound but also prevent hearing fatigue that will reduce the time you can spend mixing with fresh ears.

However not so critical as in analog, itʼs wise to keep your master fader at unity gain (0 dB) and avoid to clip it at all times, making all the adjustments in the plugins youʼre using at the master if any, at instrument channel faders or instrument outs. That way you keep track of a clean signal without surprises.

Always leave a comfortable headroom for mastering! A good dynamic range is a key word in a good mix, loud doesnʼt mean better sounding! When adding a new plug-in, adjust the output level to peaking at the same value it had on the mix before you add it.

If you having a go for yourself, Multi band compression can be wisely used on the Master, when applied with moderation can be a great plus, avoid auto gain at all costs, as it can send the master fader signal to the roof (clipping) at least + 6dB on that move alone. Not to mention auto gain will send your precious  mix down the drain.  If limiter is you last plug-in in the chain, make sure to not clip its input ever. Also remember to use the most transparent limiter you can find, usually the ones in our DAWs add some coloration, top plug-ins rule in mastering!

Hope youʼve find some useful tips here, stay tuned for the next articles. Comments and other suggestions are welcome. Please donʼt forget to read Les Brockmann’s great mixing articles.

(Special thanks to Stellita Loukas for her support and coordination.)