Impulse-Response technique

The Impulse is a short, strong sound of a sweep of sine waves of all pitches, with which a large acoustic energy with a wide frequency spectrum is sent into the church in a short time.

The Response are the reflections of the sounds from walls, pillars and ceiling. The closest walls are the first to give their reflections, the objects that are a bit further away take longer. Its volume decreases gradually and the sounds die out. There are a lot of reverberations, all with their own reverberation times that are sent via microphones to a powerful computer. The computer calculates the complex process of all reflections and stores this in a digital memory as an exact copy of the acoustics of the room.

Convolution is created by modulating sounds on the acoustic processes in the memory. Any sound sent through that memory sounds as if the sound originated in that acoustic space.

Reverberation

In a church the organ is the source of the sounds. The tones from the pipes are reflected by the walls, the pillars and the ceiling. These objects are at increasing distances from the source and therefore the reflections come later and later and their loudness decreases and dies out. The reverb moves away from the source. The effect also occurs in the mountains, when the mountaineer's call is echoed off farther away rocks, the volume decreasing evenly. The characteristic of the reverberation is that it moves away from the source and dies out in the distance. Just like the stone in the pond; the surrounding waves weaken until they die out.
The reverb stored in WET samples has the opposite effect. The microphones are far from the pipes and first register the reflections and only much later the source of the sounds. That is the situation that the churchgoers hear, they hear the echoing sounds coming towards them.

When I press a key on my Hauptwerk organ, I hear the tone before the first reflection occurs. I have to be able to hear that without delay, otherwise I cannot articulate and phrasing in the way I want to express with my playing. Someone who plays from sheet can play what is on paper and is less dependent on direct hearing, but I rarely play from sheet. To improvise I have to be able to move from tone to tone without delay. I hear how the tones form nearby and how they die out in the distance. The tones come from DRY samples and the reverb is obtained with Impulse-Response technology. The situation thus corresponds to playing the organ in the church.

How to select the appropriate IR

Impulse Response (IR) is a footprint of the acoustic characteristics of the given space (church). IR can be used to reproduce these characteristics and add them to an input signal with the help of dedicated software (such as Hauptwerk‘s convolution reverb module). The most distinctive acoustic characteristic of a space is the reverberation time (i.e. how long it takes for the sound to die away). Therefore, the IRs described in this guide are ordered according to increasing reverberation time. However, there are other features according to which you might choose your favorite IR.

RT, T20, T30 - Reverberation time (RT) is defined as the time needed for the sound to decay 60dB below the original value.

The reverb time depends on the frequency
Each frequency band will die differently. Usually very high frequencies die very quickly, the maximum RT is somewhere between 500-2000 Hz. Each IR description contains a graph showing the frequency decay for different frequency bands. The colors indicate the intensity of the sound: yellow = high energy, red = less energy, violet = low energy, black = no energy (background noise). See pictures Martini and Michaels

Sonus Paradisi - Impulse Response (IR) User Guide

To install Impulse Responses, follow the process described in chapter "Installing/un-installing/upgrading organs, temperaments, or reverbs (the component installer)" found in the Hauptwerk User Guide. In Hauptwerk, installing an IR is similar to installing an organ or temperament. In short:

1. Start Hauptwerk.
2. Select the File menu, and then select "Install organ ...".
3. Hauptwerk opens a dialog box. Navigate through the directory tree to the installation package, and select the     installation package you have downloaded.
4. Hauptwerk unpacks and installs the package. Confirm installation when prompted by Hauptwerk.
5. If there are more installation packages, repeat steps 2-4 for each remaining installation package. If you have     purchased many IRs in one order, there will be many small installation packages. It is necessary to install     each of them, one by one, to Hauptwerk.               
                                                   Impulse Response Sonus Paradisi
           PDF

To install the IR reverb

To be able to use the reverb, the control slider must first be visible
1. Go to View - Large floating control panels and then to:
2. Audio mixer, routing and voicing / panning settings set the control slider to 100
3. Select at General settings: Audio mixer for adding reverb
4. The Audio mixer screen is now visible. Choose Select this can take up to 10 seconds.
5. Choose the desired Impulse Response Reverb
6. The pre-delay, wet-mix and reverb level can be adjusted a
     little if desired, but the best result is achieved by making little changes.

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