High quality Apogee, AKG, Beyerdynamics, Digidesign, Forssell, R.M.E., Sennheiser, and Schoeps equipment is used for recordings in order to capture samples with outstanding fidelity. Long samples (usually 6-11 seconds per pipe) are all recorded with 24-bit quality and a 96kHz sample rate, making them far superior to a traditional CD’s 16-bit quality and 44.1KHz sample rate.
Much of the beauty of pipe organs, especially old organs, is found in the small idiosyncrasies of the pipes, such as initial attack and release transients, edge tone, instability, etc. These details are all captured in the samples. In many cases, more than one sample is made for each pipe, and these are used in the resulting models to better capture the pipes’ natural variation. Also sampled are the organ’s mechanical sounds, such as noises made by the key action, stop action, and blower.
The organs are sampled at night, when everything is most quiet both inside and outside the church. Since there are so many samples to make, it can take several nights of work, perhaps extending more than one week. Rain, wind, distant trains, sirens, and even mating pigeons on the roof are the enemies of good samples and fast progress.
When tremulants are provided by the organ builder, each pipe is recorded separately with and without tremulant to capture the complex effects of the tremulant on pipe pitch, speech, amplitude, etc. However, on some older models a sophisticated low-frequency-oscillator approach to tremulant is used, and this option remains on new models for cases when there is not enough RAM available in a computer to load both the normal and tremulant samples.
Three or more release recordings are made for each sample. This ensures that the model can accurately reproduce how each sample decays in the church, regardless of whether a staccato, medium, or long note is released by the player.
Although the oldest models are recorded in just two channels, more recent models contain four channels, and the most recent models contain six channels of audio (more about multi-channel audio below).
A few models are available in “dry” format. These recordings are made very close to the pipes, all but eliminating the sound of the church. Dry samples can be used to put the organ’s sound into an existing room (such as another church) without including the acoustics of the original building. Dry samples can be also used as input to a convolution reverb for a variety of room effects. For example, Hauptwerk software provides a robust convolution engine and Sonus Paradisi provides hundreds of impulse responses for an immense variety of reverbs.