Algorithmic and Convolution Reverb

Hello, I am Carlos Devizia from Argentina, and today I will write about reverb.

Reverb is a very useful effect, which belongs to the category of "Delay Effects".  We can use it to re-create a real space or to create an exotic sonic environment, not necessary inspired in the real world.

Usually, when we record an instrument, we tend to isolate it, to remove reflections in the room and remove as much noise as possible. Though, this is useful at that stage, to record the best signal possible; in the final mix, this kind of sound results unnatural. So, we can use reverb to create the correct space for our production. As we said earlier, we have different approaches to it. We can re-create a natural space, a completely fantastic atmosphere, we can use reverb to separate the instruments in different stages, like if some of them were closer than others, we can define a common space for all the instruments as if they were recorded in the same room and at the same time, etc. We can be completely creative here.

As all the effects in this category, reverb has some basic parameters to care about. The delay time is the amount of time from the input to the output of the signal, the dry/wet control balances the delayed and undelayed signal and feedback determines how much the wet signal is routed back to itself. 

Reverb units are divided in two categories: algorithmic reverbs and convolution reverbs. The first one uses a kind of formula to create the effect. An algorithm is a step by step procedure, a series of rules defined to produce a certain activity to achieve a concrete result. This is the way this kind of reverb works. On the contrary, convolution reverb works based on a recording of a real space that you apply to your sound file.

Both types have their strong and weak points. Convolution reverb is great to re-create real spaces, because you are applying to your sound a record of a reverb made in the real world, however it is limited in the way you can manipulate this. Algorithmic reverb, on the contrary, offers an incredible amount of manipulation possibilities but is does not sound as realistic as convolution reverb.

We´ll take a look at both, we use a couple of plug-ins for our examples, and it is important to say, that though from plug-in to plug-in the names and locations of the controls may vary, the concepts are essentially the same. You may find that some plug-ins have more controls than others, but the main features remain the same. So, no matter with VST you´ll be using, if you understand the main concepts you´ll be able to work with your favourite reverb VST.

Algorithmic reverb

They are usually divided in two separate components: the early reflections which are a series of short delays and the difuse reverb.

In the early reflections section you´ll find a pre-delay control, which works on the beginning on the entire reverb delaying it a little bit. We also can manipulate the space with a control named room space, room shape or a similar name according to your particular plug-in, and that will help us changing the location of the early reflections.

In the difuse reverb section you will control mainly the time parameter. This will affect the size of the room your sound is in. The high end (also high cut, damp, etc.) parameter controls the materials of the room (Some materials reflect the sound better than others, and some are softer than others and this affects the way the sound propagates).

According to the different plug-ins, you may encounter different options and possibilities, like pan controls to panoramize the reflections to the right or to the left, a freezing control to avoid the decay of the reflections, some EQ filters associated to the reverb, to enhance certain reflections on certain frequencies and attenuate some others, etc.

Let´s hear a couple of examples of algorithmic reverb applied to a short fragment of music, in this case played with an alto sax. The first sound shows the dry sound and then the sound processed with different reverb settings. All the examples in this writing do not intend to be musical, they aim to show differents effects achieved by the use of reverb.

Here are some very good freeware reverbs: 

Ambience

Epic Verb

 FreeverbToo

 Mverb

Convolution reverb

In this type of reverb we choose an impulse response, which is a file containing a record of a real reverb that we will apply to our sound. Usually convolution plug-ins have several files associated to them and there are also sets of files on the web downloadable to use with convolution VSTs. The interesting thing about this is that you have an incredible amount of impulse responses available for your use, from very realistic ones to totally strange things. The trick here is to imagine in which space you would like to hear your music and based on that selecting your impulse file. Thus, your music can sound as if it were played in a small room, in a concert hall, in a big cavern, etc. In a convolution plug -in you´ll also find some controls to manipulate the reverb.

Let´s hear a couple of examples of the sound presented earlier in this tutorial with different convolution reverbs applied to it. Let´s listen to the same sound with a couple of convolution reverb applied to it.

Here is a very good Convolution reverb freeware,

SIR

In both algorithmic and convolution reverb you´ll also have the dry/wet control to mix the signal without reverb and the processed signal. The dryer the sound it will sound closer to the listener and the wetter , it will sound far away from the listener.

Conclusion

Reverb is in nearly every element of modern music production, so it has a dramatic impact on the final results we will achieve. Changing the way we apply reverb will change our final sound, so, the more we know reverb and the way it works the more our music will be sounding in the way we want. A good starting point for using reverb is being subtle, unless we are doing something crazy on purpose, subtle adjustments provide great results.

Categories of Effects

Hello, I am Carlos Devizia a musician from Argentina. Today I will write about Categories of effects, giving small definitions of each one and providing some audio clips as examples of how they work. Please note that these examples are not intended to be musical, but they aim to show the effect itself clearly. Also be aware that, depending on how you tweak the parameters of the effects processors, you may obtain results drastically different.  And that´s a great advantage in the creative field, if we know how to use it.

We can associate different effects to different principles of sound.

Dynamic Effects

These effects are related to amplitude and they can control volume in different ways.

 In this category we find: compressors, limiters, gates and expanders.

Compressor

Essentially, this effect reduces the dynamic range of a piece by reducing the volume when it gets too loud. In this case "too loud" is related to a point called threshold or ceiling. Everything that goes above that will be reduced in a desired amount.

Limiter

This is basically a compressor with a fast attack and a high ratio.

Gate

Also known as noise gate, this effect attenuates any signal below a determined point. We also can say that basically a gate allows a signal to flow only when it is above certain level, stoping everything that is below that level.

Expander

This effect increases the difference between the loud parts and the quiet parts in an audio signal.

In the following example you´ll hear the clean sound and then processed with a compressor, a limiter, a gate and expander (in that order)

Delay Effects

These ones add slight delays to the signal and they are used to represent a space the listener is inside. In this category we find: delays, flangers, phasers, choruses and reverbs.

Delay

This effect takes an audio signal and reproduces it a certain time later, mixing it with the original signal. The amount and strength of repetitions can be adjusted by the musician, producer or sound engineer.

Flanger

This effect is achieved by taking to identical signals of audio, leaving one of them intact while delaying the second one by a gradually changing period.

Phaser

It is very similar to flanger, in the fact that this effect takes two signals leaving one untouched while processing the other one with a small delay and altering the phase of it. When both signals are mixed the frequencies that are out of phase cancel each other.

Chorus

Once again we have two similar signals. One of them is slightly delayed and usually modulated with an LFO. This gives the impression of a thicker sound and we can perceive some kind of movement in the resulting sound.

Reverb

This effect is related to the reflections of sound in various surfaces before reaching the ear´s listener. With our reverb units (hardware or software) we can re-create an existing space, enhance certain sounds (like a vocal performance, for example) or create a totally weird ambience.

Now you´ll hear the audio processed  with delay, flanger, phaser, chorus and reverb (in taht order)

Filter Effects

These effects control the timbre of sound. Among them we find : high pass, low pass, band pass and EQs.

High pass filter

This filter allows, as it is suggested by its name, to pass frequencies that are over a determined one.

Low pass filter

It is exactly the opposite of the High pass filter. It allows to pass the frequencies that are below a certain point, attenuating the ones that are over that point.

Band pass filter

It allows to pass the frequencies that are in a determined band of frequencies, attenuating those that are below or above that range.

EQ

The EQ affects the timbre of the sound by enhancing or attenuating certain frequencies (boosting or lowing frequencies). It is a vital part of the music production. It can be used both as a corrective tool and as a creative tool. You can find different types of equalizers: graphic equalizers, parametric equalizers and paragraphic equalizers.

In the following example you´ll hear the audio processed with a high pass filter, a low pass filter, a band pass filter and an EQ filter (in that order).

Conclusion

As musicians, producers or sound engineers, it is vital for us to understand each category of effects, how they are produced and which impact they have on an audio source. This will give us the opportunity to use them in a creative way, knowing exactly what we are doing and achieving the results we want to achieve instead of random results.

Sound: Propagation, Amplitude, Frequency and Timbre

Welcome to this blog everybody! My name is Carlos Devizia and I am a musician from Argentina. You can find more about me and my music in this blog.

Today, I want to write about sound and its properties.

We hear sounds all around, all the time. But why do we hear them and how can we recognize one sound from others?

Well, this is because there are some properties that belong to sound. And we´ll talk here about it. We´ll also conclude why it is important for us, as musicians, to know about them.

Propagation

First of all, sound needs a media to travel. Basically, sound is produced by a vibratory movement and transmitted through some media to our ears. The media can be a lot of different things, air, water, metal. Some media are great conductors of sound and some other ones are very poor conductors of sound. In a vacuum environment sound cannot travel, that´s why in space no one can hear you scream :), as you probably know.

But, back to Earth, sound produces a movement, this movement consist of two parts compression and rarefaction. And the movement thus produced travels from the origin of the sound towards our ears. This movement follows the same direction of the sound. This means that the motion of compression and rarefaction is parallel to the direction of the sound, not perpendicular to it.

Several factors determine the speed of sound. The media itself has an influence. Thus, for example, sound travels faster through metal than through air. You probably have seen lots of movies in which someone puts his ear down to the railroad track to hear the train coming. The more elastic the media is, the better the conduction of sound will be. On the contrary, soft and porous media are very bad conductors of sound.

In the air, the sound travels at a speed of about 340 meters per second. However this is not an exact number. Factors like temperature or elevation has effect on the speed of sound. It is estimated that for each degree that temperature increases, the speed of sound increases in 0.6 meters/second.

Generally we speak that the speed of sound is:

340 meters/second

1 foot/millisecond

1 kilometer/ 3 seconds

1 mile/5 seconds

As musicians, producers or sound engineers we can take advantage of this characteristic of sound. When you listen to a sound, you can perceive distance and procedence of that sound. It is not the same to hear someone speaking in a low voice beside us, than someone who speaks in the same way at several meters of us. Also, we can perceive where is located the origin of sound. It is right in front of us? Behind us? It is located slightly to the left? Completely to the right?

By the use of different effects we can re-produce a natural environment or create a totally strange atmosphere, working on the propagation of sound and the way we perceive it.

Effect we´ll be using to achieve this goal are: flanger, delay, reverb.

Amplitude

There are several type of waves. As we said before, they move in the direction of sound, but we represent them by different means to visualize them. This is important to understand some sound phenomena.  In the following examples we´ll use the image of an oscilloscope, which is a valuable tool for analyzing sound.

We said that sound involves a process of compression and rarefaction. The intensity of this process is what we call amplitude. Our perception of the amplitude is loudness. Here, it is important to point, that though these words may seem synonyms, they are not.

In practical terms, the more the amplitude, the louder the sound we will perceive. (compare the graphic example of a soft sound and a loud sound and listen to them).

To measure amplitude we use a unit called decibel (DB), which is, in fact, a relative unit. Now, this is a tricky word, as it is used in different contexts. If we are talking about decibels in the air, we talk of DBSPL (decibels sound pressure level). 0 DB is the quietest sound we can hear and from that it goes above. The point in which our ears suffer is called "threshold of pain".

Some examples of approximate DB levels:

Whispers - 12 DB

Soft music - 25 DB

Quiet street - 43 DB

Conversation - 60 DB

Car - 68 DB

A Factory - 75 DB

A traffic jan - 83 DB

Powerful Hi-Fi system - 90 DB

Symphonic orchestra at full level - 102 DB

Thunder - 109 DB

Rock Concert - 115 DB

Plane - 120 DB

Threshold of pain - 130 DB

But, some lines above we said that decibels was a tricky word and this is because it is also used in the computer like DBFS (decibels full scale), and here 0 DB is the loudest thing that can be represented by the computer. From there the values go down in form of negative numbers.

It is useful to understand the concept of amplitude, for example related to audio gear. Here we find what we call dynamic range, and which is the range between the quietest sound that a device can handle (before that level there is only hiss) and the loudest level that the device is capable to deal with (over that there is distortion, cracklings and non-desired upper harmonics).

It is also useful to understand the concept of amplitude to use that in a creative way. Once again we can use effects to process amplitude in a creative way: Our tools here will be compressors, limiters, gates and expansors.            

Frequency and timbre

As we said, there are waves of compression and rarefaction. The quantity of those waves determines the frequency of a sound. We measure it using a unity called Hertz, a Hertz is one in a second.

We perceive this as pitch. Once again, like amplitude and loudness, frequency is a measurable term, while pitch is our perception of that frequency.

The higher the frequency the higher the pitch we will perceive. So a sound of 440 Hertz will be lower than a sound of 8000 Hertz, for example.

In the oscilloscope images we can see a low frequency wave and a higher frequency wave. You´ll notice that amplitude does not change. This is because properties of sound are independent between them.

Usually, we tend to say that human beings perceive between 20 hertz and 20000 hertz, which is not totally true. More likely we are able to perceive to about 18000 hertz. And not all ears behave in the same way. We tend to lose perception of high frequencies while we grow up. Also, women tend to hear better higher frequencies than men do.

Now, let´s think for a moment, two sounds were played at the same frequency with the same amplitude we should perceive them in the same way. But here makes its appearance another element which is timbre. When a sound is produced, we can hear a fundamental frequency, but also lots of frequencies that are present too in that sound. These secondary frequencies are called partials, and if they related to the fundamental in a perfect mathematic way they are called harmonics. These frequencies colorize the wave and make it less pure, giving to its sound its proper voice. This is why a piano sounds like it does, and a cello sounds with its own sound, and so on. Let´s take a look at the way the oscilloscope shows the sound of some instruments.

The knowledge of this fact is useful, for example, to wind players that can obtain new sounds enhancing harmonics while they play, and thus obtain different notes in one playing position.

We can use different filters to work on timbre and frequency. EQ is our main tool in this aspect. We can use it in two ways: to correct audio files that need some changes in their frequencies to sound more natural, boosting some of them and lowering some others; or we can use the EQ in a creative way, boosting and lowering frequencies to achieve results that are different from those that can be heard in the real world.

Conclusion:

The knowledge of sound and its properties will benefit our creative work as musicians. Sometimes musicians tend to forget that they are working with sound. Knowing its properties will help us to manipulate it in a creative way, to reproduce a real environment, to create a completely strange atmosphere, to understand why the song we are working in does not sound in the way we want, to choose the proper effect in every situation.



Intruments photos taken from wikimedia commons:
Drums: Stephan Czuratis 
Nylon Guitar: James anderson
Clarinet: Ratigan
Alto Sax: Jana C.