The Dry sample sets are recorded close to the organ pipes, sometimes even inside the organ case. For this reason, the recording has captured all those small strange noises which sometimes accompany the pipe speech. Although amazingly natural, such sounds may not be pleasant to listen to. The resulting sound of the sample set is rough, sometimes ugly. As if you put your head few centimeters from the pipes when the organ is played. You do not want to be inside the organ case when a pipe organ is played.
The dry sample sets exists for special purposes only. They can be used in churches and other reverberant spaces as temporary replacement of real pipe organs. For example, we have used the dry sample set of Caen every year for the live performance of the organ part of Schnittke's Requiem with the Ensemble Inégal, where it gives fantastic results in places, where there is no suitable real pipe organ. The dry sets can also be used for special purposes of acousticians and sound designers, or composers and similar persons in conjuction with a chain of audio plug-ins, such as reverbs, equalizers, compressors ... to be blended with other sounds seamlessly.
In all these circumstances, the dry sample set must be voiced extensively to match the acoustics of the given space and the qualities of the audio system used. The dry sample sets are not to be used "out of the box"! The dry sets are used in many churches in Poland and in Slovakia, to my knowledge, as temporary replacements to pipe organs. I visited some of these installations and I performed the voicing on the place. It is usualy 3-4 days full of work, starting with acoustical measurements of the space and of the audio system, creating custom IRs to compensate for the response, then, using Hauptwerk voicing to fit each stop and each virtual pipe of each stop into the ensemble, achieving ballanced sound of the full instrument. Although the same sample set used (usually Rotterdam dry, or Caen dry), the result sounds very different on each place, depending on the acoustical conditions, and my own artistic views.
Sometimes users think that the dry sample set plus IR reverb will give the surround sample set as the result. No. With the IR reverb and with extensive voicing of the dry sample set, you can achieve eventually marvellous audio, but not the sound of the surround sample set.
Recommendation: for home use, always purchase the surround (wet) sample sets. Never buy the dry sample set for home use to prevent disappointing results.