Convolution reverb

In Hauptwerk 4 reproducing the reverberation was only possible by using WET samples. Not the good reverb effect as the organist and the choir members are used to hear. The reverberation comes to you instead of moving away. But people who only know the organ from listening to it during church attendance; it was accepted as real reverberation. A system that fully corresponds to the reverberation of the church had been around for a long time, but Brett Milan did not want to implement it in Hauptwerk yet. It has now been made possible in Hauptwerk 5. It is the Impulse-Response technique in the recording and the convolution in the reproduction.

Impulse
The Impulse is obtained by recording the reflections of the church after an impulse was given. The impulse is a short, strong sound from an alarm gun or a sweep of sine waves. It is about sending a large acoustic energy with the widest possible frequency spectrum into the church in the shortest possible time.

Response
Response are the reflections of the sounds from walls, columns and other objects. 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 it in a digital memory as an exact copy of the acoustics of the room.

Convolution
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.

When microphones record the sounds a short distance from the pipes, they are stored as DRY samples. If then the reverb from an Impulse - Response recording is used, it corresponds to what the organist hears at the console in the church. Then the ideal situation is reached and the organist in the living room hears the same as the organist in the church.

Now that convolution reverb ideally provides the acoustics, there is no reason to use the inferior WET samples anymore. In my Hauptwerk organ I only use the DRY samples with the convolution reverb. For example, I hear the sounds of a pipe organ at a short distance and the surrounding reverberation lets it die out in the distance. A church organist hears the organ sounds and the reverberation in the living room as in the church.

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.

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 IR's can be used

Impulse Response use is covered in detail in the Hauptwerk User Guide chapter "Audio routing and impulse response reverb, part 1 and part 2". In short:

1. Open the Hauptwerk Audio Mixer.
2. Select the desired bus to which you wish to apply the IR.
3. Click the Select button. It takes about 10 seconds to see the list. Impulse response reverb.
4. From the list of available IRs, select the one you wish to apply to the bus.
5. You can adjust the pre-delay, wet-mix and reverb-level if desired. For best results, use small adjustments.

Select bij View: Audio Mixer Routing and Voicing/Panning Settings for adjusting the volume of the reverb.

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

Eén stereo-kanaal
Veel amateurs hebben het vreemde idee dat de orgelklank beter wordt als er meer kanalen worden gebruikt. Dat stamt nog uit de tijd van orgels met elektronische toonopwekking, maar als Hauptwerk gelijk moet klinken aan een Pijporgel mag er niet meer dan één stereokanaal wordt gebruikt. Dat kanaal moet bevat DRY samples bevatten, dus klanken die op korte afstand van de pijpen zijn opgenomen. Deze zijn heel goed te intoneren, waardoor ze met een volume voor de huiskamer net zo klinken als in de kerk.

In Hauptwerk 4 waren WET samples, dus opnamen die ver van de pijpen waren gemaakt, de enige mogelijkheid om de akoestiek van de kerk over te dragen. Ik heb ze nooit gebruikt. Een Lexicon MX300 gaf een betere akoestiek.

Nu convolutiegalm op ideale wijze de akoestiek verzorgt is er geen reden om de inferieure WET samples nog te gebruiken. Vaak wees een organisten Hauptwerk af nadat ze een orgel met veel kanalen hadden gehoord. De klanken daarvan zijn geen goede voorbeelden van de echte kwaliteit van Hauptwerk. Mijn Hauptwerkorgel is dat wel en kan direct met mijn pijporgel worden vergeleken.
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