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In this first installment of the Foundations of Audio series, author Brian Lee White shows how to improve the sound of a mix with compressors, limiters, gates, de-essers, and other dynamic processors. The course explains the fundamentals of sound waves, and amplitude, explores common compressor controls, and shows how to eliminate unwanted noise using gates and expanders. The course also demonstrates best practices in compression and limiting in a variety of audio applications and covers sculpting the attack and decay of individual notes with transient shapers and applying frequency specific dynamics control with multiband compressors. Exercise files accompany the course and include special Get in the Mix session files.
Let's take a look at how to apply compression to a single note, using it to draw out the attack or sustain of a signal and letting that note punch through dense musical sections of the mix. This type of compression is often referred to as envelope shaping or transient shaping. A shape of a note's waveform is called its envelope. The envelope describes how a note evolves over time. Think of envelope as the trip a signal's wave form takes from initial development through final decay. Let's take a look at a snare drum note's envelope. We start with a sharp transient, this is referred to as the attack.
This sharp transient is followed by a brief sustained and final release period as the sound dies out. Because a compressor reacts to a signal's amplitude as it changes over time, we can use compression to play with the shape of a signal's envelope. Listen to the snare drum without any compression, pay attention to the sound of the attack and release. Now listen to the same same snare with compression applied and listen for how the sound has changed. Notice how in the compressed version, the attack of the signal is pulled up and has more punch. This is achieved by adjusting the attack time of the compressor to allow a bit of the original transient through before being compressed.
An attack time of between one and ten milliseconds works great for this. But any longer, and I risk missing the transient altogether. After making up the game from the compression, what we end up with is a larger transient, or initial attack portion of the sound than we started with Because the body or sustained portion of this sound has been attenuated, thus changing the dynamic relationship between the two. A muted copy of the processed wave form has been provided as a visual reference underneath the active snare track. Now listen again to the snare and the context of the full mix and pay attention as it automates the settings to apply the compression.
I'm exaggerating a bit here, so you can really hear the compression. But notice how the punchier snare helps the drum kit drive the song. Dynamics are all about relative relationships and amplitude, and in this case I've changed the relationship between the attack and the rest of the snare hit. The more aggressive the threshold and ratio settings I use, the more distance I create between the transient and the rest of the snare hit. We can achieve the opposite effect by using fast release times. Let's take a listen to very fast release time on the snare drum. Again, I've exaggerated the effect, so you can really hear the change in the shape of the snare envelope.
>> Trouble bound, we hit the town. And I'll never forget, that sound. >> By allowing the compressor to compress the initial transient body of the snare drum, and quickly release the compression before the softer decay section, we can use the makeup game to inflate the tail of the signal and draw it out longer in time. Notice how I'm driving the compressor a little harder here. Achieving more gain reduction.
This trick works best with more aggressive threshold and ratio settings. Feel free to zoom in and look at the processed example tracks waveform to better visualize what's happening. You want to watch your attack when you reach these levels of gain reduction. Even a small amount of transient escaping through un-compressed can eat up all your head room, and clip the output. This trick doesn't work on every kind of material, or with every compressor, so use your judgement. Sometimes I split the track in to two, and process one for a sharper attack. And another for more sustained.
And then blend the two to taste. Some compressors are better at each of these tasks than others. In order to achieve effective envelope shaping with the compressor, we're generally looking for a processor with a very fast attack and release time. A slower compressor or one without attack and release controls may not be fast enough to really draw out the envelope precisely.
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