Understanding the reason we use vocal compression is very useful, and absolutely necessary for a music producer,
with that said I wrote this article to give an answer of what it means to compress vocals,
and I will help you understand why you need to apply compression to your vocals.
What it means to compress vocals and why we do it is basically to reduce the dynamic range between the loudest and the quieter parts of a vocal.
Compression performs the function of boosting the quieter signals whilst keeping the louder signal moderate enough not to distort.
Compression acts as the device that controls the dynamics of the vocal. It achieves this by being able to provide consistency in both the louder and quieter parts of the vocal.
The truth is we are humans and not machines;
therefore recording a vocal with no dynamic range is almost if not always impossible.
Keep reading as i share the important things that make compression useful and what makes it an invaluable tool in music production.
Types of compressors
VCA Compressors generally spot and have full control over all the parameters ( I.e . Ratio, threshold, attack, release, knee etc) which makes it applicable in both mixing and mastering.
FET Compressors work by passing the audio signal through a field effect transistor, this done mainly to have more control over the gain.
these types of compressors are great for parallel compression (A process of mixing a lightly compressed audio signal with a highly compressed version of the same signal).
Tube Compressors have slow attack and release times as compared to any other compressor,
it is for this reason that tube Compressors tend to add colour to the vocal, this color may be what you’ve heard as a “vintage” kind of sound.
Optical compressors work by influencing the dynamic range by using an optical cell and a light element.
As the amplitude of the audio signal increases the light element emits a light signal which tells the optical cell to attenuate the output signal.
What is ratio?
The ratio in vocal compression is basically where you determine how much compression you will actually need
and how much you intend to apply to a particular signal.
Ratio works hand in hand with the threshold,
which is how loud a signal should be before compression is applied,
for example; the ratio is set to 4:1 ;
what this means is that the input signal coming into the compressor will have to cross the threshold by 4db in order for the output signal to increase by one.
The ratio determines the gain reduction that the compressor applies when the input signal crosses the threshold.
Lower compression ratios tend to apply a subtle level of compression and will have the input signal sounding a lot more natural and more transparent;
the natural peaks will also be reduced.
The lower the compression ratio the less dynamic control an input signal will have.
Medium compression ratios will apply a more gentle dynamic control, and the vocals will tend to have a much fuller sound.
The signal will retain its natural sound,
and a medium ratio will allow you to have more control over the transients of the signal flowing through it without causing any significant change to the tone and overall punch of the signal
A Higher compression ratio on the other hand will cause a more noticeable aggressive and processed sound.
The best application for high ratio is to have extreme control over the tone shape and the dynamic control.
This kind of heavy ratio when used to the fullest can cause lack of clarity and presence in the vocal.
What is attack and release?
Attack refers to the time which it takes for the signal to become compressed after it goes above the threshold level.
faster attack times range between 20 to 800 milliseconds,
but this will greatly depend on the brand and the unit of the compressor you decide use.
Fast attack times can create distortion because they able to modify a slow moving frequency.
Depending on the brand of the compressor you’re using;
attack times may be expressed as a slope on a graph (measured in dB per second),
therefore it is important to use a compressor that you are familiar with.
The release time is the duration it takes the compressed audio signal to revert back to the original uncompressed sound.
Release time is simply the opposite of the attack time, and they are much longer than attack times (generally ranging from 40ms to 60ms to 2 to 5 seconds)
They can also be expressed as a slope in dB per second rather than the actual time;
this will depend again on the brand of the compressor you’re using.
Soft and hard knee
Knee refers to how a compressor is able to transition from compressed states of the signal to the none compressed.
Think of it as how quickly the compressor clamps down on the audio signal once it exceeds the threshold
This will differ from compressor to compressor.
So then what is soft knee compression?
Soft knee compression is a type of compression in which the onset of compression is gradual,
The compression in this case is added gradually to the signal, starting out before the threshold and increasing towards the ratio until it is passed the threshold.
Soft knee compression is more subtle.
with hard knee compression,
the gain reduction applied to the signal typically starts and occurs the moment the signal exceeds the threshold.
Compression and limiting maybe used separately or individually in music production but the reality is they are one and the same thing.
Think of Limiting as extreme compression.
But keep in mind that not ALL limiting is compression.
Limiting is a result of using a compression ratio which results in the prevention of the audio signal from exceeding a digital ceiling.
Limiting drastically reduces the dynamic range usually to almost equal to zero and
they are heavily relied upon in the mastering process, usually the threshold is raised so that not all dynamics are reduced.
A high threshold allows you to control excessive high peaks whilst keeping a fair amount of range.
Therefore the person using the limiter has to know why they want to use a limiter,
Most producers making music from home use limiters to make the mix louder,
but what comes with this loudness is a loss of range in dynamics so make sure you use your limiter accordingly and apply it only when necessary.
How many compressors do you need for vocals?
I recommend having two compressors for a vocal,
you’re going to need one to be a faster compressor that is able to control the peaks and you will need the other one to be slower in order for it to control the dynamic range of the vocal.
Why do compressors sound different?
Compressors sound different because they are designed differently, they are independently designed to serve a particular purpose.
Compressors differ in attack times, release times and thresholds therefore the time they generally get to kick into the vocal will greatly differ depending on the parameters that you specify within the compressor.
In not so technical terms, compression simply makes the overall volume of the vocal more consistent in order to ensure that there aren’t any louder parts or quieter parts in a vocal.
Therefore if a vocalist is singing with an inconsistent vocal projection, it is the job of the compressor to level out the entire vocal and make the volumes in the range equal.
Compression is a very important aspect of any kind of audio production, and it is added to a subtle degree to ensure that the vocal sounds more natural.
This is achieved by compression units being able to control the dynamic range of the audio signal whilst keeping distortion at bay.
Related Articles You May Find Interesting
Should I Use A Compressor When Recording Vocals?
What Effects Make Vocals Sound Better?
Using Compression to Help Vocals Sit in a Mix – iZotope
Vocal Compression: Why It’s So Important and How to Achieve It – Mastering Box
Vocal Compression: Learn How to Mix Like the Pros – Musician on a mission