Fundamentals of Sound in Post Production

Other Resources

Preparation for Blog Post Creation and Note-taking


“Sound is Half the Picture” – Steven Spielberg

Tools for Mixing

  • Adobe Premiere Pro
  • Adobe Audition
  • Avid ProTools
  • Apple GarageBand
  • Audacity

NLE – Non-linear editor like Audacity, GarageBand, Adobe Audition, Avid Pro Tools, etc.

Equalizer – An equalizer boosts or cuts the amplitude of certain frequencies which alters the harmonics or overtones resulting in the change of the character of the sound.

First Order Filters

High Shelf – This type of equalization, called a first order filter, is the simplest kind of equalization to perform using electronic components. This is found on your basic consumer hi fi systems.

Low Shelf – Cut the sound of the low frequencies in our recording below 100Hz, for example.

High-pass Filter – Lets all the high frequencies pass, eliminating all the low range.

Low-pass Filter – Lets all the low range pass and killing off the high frequencies.

Second Order Filters

Peaking Filter or Parametric Equalizer – Target a more specific range of frequencies. This is often called the and it has three settings:

  1. The frequency, which is what frequency you wish to target,
  2. The gain: how much you want to boost or cut that frequency
  3. The Q, or quality factor, which is how wide the parabola of the adjustment will be.
    • High Q values will have a steeper slope.
    • Sometimes Q is expressed in octaves – the more octaves a Q has the more wider and gentler the effect.

Notch Cut or a Band-stop Filter – Really high Q filter used to completely eliminate a particular frequencies. Used to eliminate constant frequency based noise like a electronic hum or to prevent feedback in a live audio setting.

Graphic Equalizers – Commonly found on mix boards, they behave the same way as parametric equalizers except instead of selecting specific frequencies and changing the q value, all the frequencies are presented as sliders with a predetermined interval and q value.

Why do we use equalizers? – Essentially three main uses:

First: Fix inadequacies in the recording: Microphones aren’t perfect and some have a specific frequency response and you may want to use the equalizer to compensate and create a flatter response.

  • You can also target specific hums with a notch filter and eliminate them or use a high pass filter to cut low range rumble caused by wind noise.

Second: Use EQ when you’re mixing audio sources that are competing in a similar frequency space .

  • A common occurrence when mixing voice over with a background music track, if you cut the background music in the 1200 HZ range, the sweet spot of human voice, you can make some more room for dialogue or voice over tracks:

Third: Making the track sound better – or just different.

  • For instance boosting the bass frequencies on a dialogue track, say around 160 hz will add power to human voices, but too much can make the track muddy and unintelligible.
  • You can add a bit of presence by boosting the 5kHz range but again too much will cause ear fatigue.
  • Sibilance or ess sounds can be found between 4 and 10 kHz, you can boost this for more of a clear sound or cut it to get rid of harsh ess sounds.

Instrument Frequencies – Refer to a mixing instruments chart available online that give you a general guideline for which frequencies to target depending on the instrument.


Dynamics – General loudness of a passage of music from piano which is soft to fortissimo which is loud and forceful.

  • Dynamics in sound engineering is same concept – the dynamic range is the difference from the very soft to the very loud. Sometimes we need to compress that range – to make the difference between soft and loud passages smaller.

Compressor – Makes the difference between soft and loud passages smaller.

  • Compressors help smooth out sudden increases in volume caused by momentary changes of distance from the mic or just natural changes in volume.
  • Compression makes the audio sound more powerful and louder than it really is.
  • A compressor works by essentially squashing down sound that goes above a certain threshold, based on a pre-set ratio of 2:1, 3:1, 4:1, or higher.
  • 2:1 compression means for ever 2 dB increase in volume above a threshold like -12dB from the input, there will only be a 1 dB increase in output volume. 2db goes into the microphone and 1db comes out the speaker.
  • A more drastic compression would be 4:1, for each 4dB increase of input there would only be 1 dB increase in the output.

Compressor Attack and Release – determine how quickly or slowly they kick in.

  • Too fast and you can get a pumping sound, too slow and spikes in the audio can slip through.
  • Once we have compressed the dynamic range, we can safely boost the entire track to make everything generally louder if desired.

Limiter – A limiter essentially prevents peaks from going over a specific target generally used for broadcast and they have very short attack and release times.

  • A limiter has a high compression ratio of 10:1, 20:1, or even 100:1.

Expander – The opposite of a compressor.

  • Expanders are generally only used for the quieter parts of the dynamic range.

Noise Gate– A noise gate is one kind of expander. Essentially like a high pass filter except for amplitude.

  • Anything louder than the threshold will get through, anything lower than the threshold will be expanded down into nothing.

Multi-band Compressor – Combines the best of EQ – the control of harmonics and overtones with the control over dynamic range that a compressor has.

  • A multi-band compressor breaks the track into different bands of frequencies which you can independently apply compression.

Fast Fourier Transform or FFT – A noise reduction tool that works by first taking a snapshot of your audio waveform – creating a profile of the unwanted sound. Then using various settings you can subtract the offending noise from the entire track.

  • Chirping – Too much FFT processing can result in something called chirping which is squirrely weird digital bird sounds. You can avoid chirping but not completely removing background noise.


Delay – Repeating of an original audio signal numerous times.

Combing – By repeating the audio with a delay of 15 milliseconds or less, we get an effect called combing where interference patterns created resemble that of a comb.

Chorusing – With a delay of 15-35 milliseconds we start getting chorusing effects where the brain is starting to perceive more than one voice or instrument is being sounded.

  • Chorusing filters can also vary the pitch and timing of the delays for more effects. This may be useful for creating bizarre and other worldly characters for your audio.

Echo – Beyond a delay of 35 milliseconds and we will begin to perceive an echo effect.

Reverb – The mixture of a large number of random and decaying echoes.

  • Advanced digital reverb generators can even simulate the time and frequency response of a specific rooms like concert halls. Echo and reverb can give your audio track a sense of space – whether that’s a large cavern or even a small hard room.

Pitch Shifting – Take a wave and squeeze the time, this is adjusting the frequency. Make the time shorter and the frequency will go up. Stretch it out longer and the frequency will go down.

Phase Vocoders / Sinusoidal Spectral Modeling – Stretch and squish waveforms making things like auto tune possible.