Technical details regarding the project:
When the OPUS BACH idea was first conceived, it was clear from the outset that a simple stereo production in CD-quality would not be sufficient to satisfy the requirements of the technical status quo in the second decade of the 21st century.
Multichannel developments ranging from surround through to 3D formats as well as the refinement of digital sampling rates (imagine a digital photo of the early 90s compared to today) are the factors setting the bar here. Since the recordings are not being released en bloc but step by step (about the length of one CD every six months; everything needs to be well prepared musically), it had to be taken into consideration that further technical innovations could already make the project look dated during production.
Thus the decision was made to produce in AURO 3D (10.1) at a sampling rate of 192 kHz.
AURO 3D was chosen because it works with 10 discrete channels. The spatial effect is therefore not produced synthetically, but purely by runtime differences between the microphones. In addition, the 10.1 configuration uses 3 layers: 5 channels in the first (surround layer), 4 channels in the second (high layer), and one channel in the third (top layer), known as the ”Voice of God”. The advantage of this confi guration is that all current formats, starting with stereo (mp3, CD, 192 kHz), through 5.1, 2+2+2 and right up to AURO 3D, are practically ”downwardly compatible”.
192 kHz sampling rates represent what is currently technically possible; I leave to others the answer to the question of whether this is meaningful and actually audible, since these discussions have already taken place very frequently (already with regard to 96 kHz). In the fi nal analysis, we are making available an OPUS which from a technical viewpoint alone provides all technical formats available at the present time, and can respond fl exibly to new standards (there is, unfortunately, currently no streaming format for AURO 3D in particular).

A few thoughts concerning the recording:
The problem of positioning the AURO 3D microphone array was, based on years of tried and tested 5.1 surround arrangements and the experience of recording three CDs in St. Michael’s, to position this at a height of over 10 metres and in a way that could be reproduced.
Since it was not possible to suspend or anchor the microphones, all that remained were months of experimenting with carbon and other lightweight materials, which ultimately led to a construction with, on the one hand, microphone distances wide enough to ensure the appropriate runtimes while on the other being light and stable enough to perform its task safely on an overhead tripod at the desired height. For the sake of clarity, the three front microphones (LCR), forming the ”Decca Tree” providing the stereo sound pattern, were arranged more directly than in previous, more romantic organ productions in St. Michael’s Church, which has a considerable echo. This was done, on the one hand, in order to facilitate following the clarity of Bach’s voice leading and, on the other, to achieve a truly homogeneous balance between all layers when playing in surround or 3D.

Martin Fischer
(Translation: Laura Park)