The Fundamentals of Sound in Audio Post-Production
The post-production side of audio is constantly evolving. Ever since its inception, many different tools have been used by sound and audio professionals to craft compelling soundtracks. In this blog post, we’re going to establish the fundamentals and look at the digital audio workstation tools for mixing and refining a film’s soundtrack.
The Equalizer
Before we get started, it’s important to mention that in this lesson we’re going to be diving deep into shaping sound, covering and providing a fair amount of information about several aspects involved in the audio post-production process, as per discussed in previous blog posts.
The first tool or weapon in every audio post production studio or sound editor’s arsenal is the equalizer. What exactly is an equalizer? In real basic terminology, an equalizer is a device or software mostly used as a tool that boosts or cuts the amplitude of certain and specific frequencies, which, without any editing, alter the harmonics and overtones, resulting in the change of character of the intended sound.
Imagine the audio response of a wave as a straight line on a graph, with the X-axis representing the frequency, going from low to high, and the Y-axis representing the amplitude. Let’s say, for the sake of this example, that we want to boost only the high frequencies — everything above 5,000 Hz. Now, our straight line is now broken into two different levels with an evident slope in between. This is traditionally called a high shelf.
This type of equalization is called a First Order Filter, and is perhaps the simplest and most used kind of equalization performed using different electronic components, and is the one you unconsciously perform in your car radio or household radio systems.
Now, to continue, let’s say we want to cut down the sound of the low frequency on a recording below 100 Hz. This change is commonly referred to as a low shelf cut. But let’s assume we want to go into the extreme and eliminate all the sound from above or below a certain frequency. The shelf is now known as a Pass Filter. A High Pass Filter essentially lets all the high range pass, getting rid of the low range; whereas a Low Pass Filter does exactly the opposite: it lets all the low frequencies pass and kills the high ranges.
If we wanted to target an even more specific range of frequencies, we would need to resort to a Second Order Filter, which includes a peaking filter or a parametric equalization, and has three different settings: the frequency, which is the frequency you specifically want to target; the gain, meaning how much you want to boost or cut the aforementioned frequency; and the quality factor, also known as ‘Q’, which means how wide the parable of adjustment will be.
Normally, high Q values will have a steeper slope (remember we’re picturing all this information in a graph with an X-axis and a Y-axis). Sometimes the Q value is expressed in octaves. The more octaves the Q values has, the wider and gentler the desired effect. A really high Q filter is traditionally used to completely get rid of a particular frequency and is sometimes called as a notch cut or the band stop filter. The band stop filter is normally used to eliminate noises like an electric hum or to prevent feedback in a live audio set.
Another type of equalizer you may come across are graphic equalizers. These are normally found on mix boards and behave the same way as parametric equalizers, except that, instead of selecting specific frequencies and changing the aforementioned Q values, all the frequencies are present with predetermined intervals and Q values.
Now, after having laid out all this information, the question still remains: how and why do we use equalizers? There are essentially three main purposes:
Fix Inadequacies in recordings
Microphones, though highly technological, are not perfect. Some have specific frequency responses, and by using an equalizer sound professionals are able to compensate for a flatter response, eliminate electronic hum, or, by using the high pass filter, eliminate wind and environmental noises.
Mixing Audio Sources
Sometimes there are different audio sources competing amongst each other in the same frequency space. It traditionally occurs when sound professionals are mixing voice-over with background music. By using an equalizer, audio professionals can make room for the human voice without compromising the score or any other voice-over tracks.
Make Everything Sound Better
The third reason for using an equalizer is rather a creative reason. By making out the most of an equalizer, audio and sound professionals can simple make everything sound much better. Or different. For instance, in many films, just for effect, some directors want to boost the bass frequencies during a specific dialogue to add power and contribute to the general storytelling.
