Hi there. This is Hyon Kim, R&D Engineer involved in the Inspired Art Project,.

In my last blog, I talked about the outline of the Inspiart Project. In this blog and the next blog, I would like to talk about effects in mixing. I briefly explained the four types effects of mixing; reverb, compressor, equalizer, and panning in my last blog. Today, I would like to explain reverb and compressor more in depth.

Reverb (delay)

In a room or a space, sound reflects back and returns to the place where it yield. It is like, when you drop a stone in the water tank, waves occur and bounces back from the wall of the water tank. It is the same as the phenomenon. Echo is also a type of reverb. Reverberation is considered as a very important factor in evaluating quality of a concert hall. This effect always exists everywhere in a natural space. There is an artificial anacoustic chamber, but it said to be a very uncomfortable room for people.

Even in music, reverberation plays an important role in creating the atmosphere of songs.

Signal processing (mathematical) this reverb is defined by a finite impulse response.

It looks difficult to understand. bi is the part that determines how fast the sound decays, and N is a number saying that how many times it sounds. x is an input sound and y is an output sound. The sound that added it represents a series of sounds. Signal addition is said as convolution in mathematics.

Basically, the reverberation of a certain space can be measured and reproduced on a sound. A short and loud sound, such as a explosive sound, is utilized to measure the speed at which the sound returns and the time is considered as a parameter of reverb of the space. If you multiply the time parameter and convolve with the sound source you want to reverberate, you will get the effect as if you were playing music in
that space.

Modern electronic pianos let you set a room, a church, a concert hall, and so on as a reverb effect. As a result, the sound coming out off the speaker sounds like it is playing in it. This is a well-known example
of reverb effects.

Compressor

Next is the compressor. The compressor adjusts the strength/loudness and softness of the sound. This function compresses and amplifies at a constant rate sound exceeding a certain threshold. This
factor/parameter is called ratio. In most cases, this ratio is in the range of 1: 4 to 1:10. In other words, sounds that exceed the threshold will be reduced to 1/4 to 1/10. The function set a sound to
a certain level when exceeding sound is called limiter. It does not consider ratio but just a constant number to set. With this compressor you can make the sound more powerful in pop musics and more delicate in classical music.

You can also apply this idea to adjust the attack. This makes the sound crispy or soft by making sound reach to maximum volume very quick or slowly by certain ratio. In other words, time t sets how quickly the
compressor runs. The opposite function is release. Release determines how long the compressor will keep working.

I explained the core parts of reverb and compressor. The Inspiart project is to create system for automating these effects. The path to the goal is still steep and long way to go, however, I would like to enjoy along the way. The team is expanding and we are hiring! So please contact us from the recruitment page if you are interested.

Next time, I would like to introduce equalizer and panning.

Reference:
FIR filter, https://en.wikipedia.org/wiki/Finite_impulse_response