Tjyylli

What I'm trying to get a feeling for is how well an electronic organ can mimic the sound of a pipe organ. I know there are very advanced electronic organs where every single note for every stop is recorded by playing each note on a real organ. Even fluctuations in wind pressure and other effects can be simulated.
Can a general listener hear the difference between the two? I'm interested in modern electronic organs.

For some background, I'm asking this because in my church we need to decide between investing in replacing major parts of our small pipe organ (only one manual, 10 stops) or investing in a new electronic organ with speakers and a subwoofer.

The benefit of the electronic solution would be lower periodic maintenance costs and more options (manuals, stops, swell pedal, etc.), but the key question is: Can it sound the same as a pipe organ?

The problem is that demo recordings are mostly useless for that kind of decision. All you get to figure out is whether a recording of a pipe organ sounds like a recording of an electronic organ, not whether a pipe organ sounds like an electronic organ. Since these days electronic organs are digitized pipe organs, the interaction of the individual pipes with the actual congregation room is not there. Things get more misleading if you record the electronic organ directly since then only the original room acoustics from the digitization (and you cannot just drag a pipe organ into an acoustically dead recording chamber) remain with none of the congregation room acoustics. Such a recording of an electronic organ will be mostly indistinguishable from recordings of the originally used organ in its original setting, but if you think that a good speaker system replaying a recording will be indistinguishable from actually playing the pipe organ is sort of optimistic.

Now the kind of organ you are replacing is rather small. If you hope to budget commensurate with what its repairs would cost, the electronic organ will not be of the overly impressive kind either. That's sort of the size factor the original Hammond organs (before getting abducted into Jazz, Rock, and whatnot) tried competing with.

I'd be pretty suspicious expecting large organ performance from something on that budget so you really should listen to (and play) the intended instrument live in some venue of similar size to that of your congregation. Recordings will not tell the real story. So budget some travelling costs into your decision-making process.

To make an electronic organ sound like a conventional pipe organ, the most important component is the sound reproduction itself. Even on your tiny one-manual ten-stop instrument, a full 8-note chord can sound 80 pipes simultaneously. On a larger instrument, there may be several hundred individual pipes sounding together.

In contrast to this, an electronic instrument only has a very small number of loudspeakers. That has two consequences.

The first is that there are only a small number of physical locations where the sound is produced. In a pipe organ, very pipe is at a different location, and the sound creates a slightly different reverberation pattern both within the instrument itself (e.g. the location of the different pipes in a swell box) and within the whole building. The complete ears-and brain system of human hearing has remarkably accurate direction-finding capabilities, and though the difference in position of every pipe isn't consciously heard, it is certainly affecting the overall hearing process. Because of the effects of the building acoustics, often a single sustained note on an organ can sound quite different if the listener moves only a few inches. Since humans subconsciously make continuous small head movements as part of the direction-locating function of hearing, these effects are significant.

On the other hand, an inexpensive electronic instrument will have a small number of loudspeaker cabinets, each reproducing the sound of many (or all) the pipes, and this detailed spatial differentiation is lost.

The second problem with a small number of loudspeakers is the distortion produced when one speaker reproduces two simultaneous notes. It is impossible to devise a reproduction system that is completely linear, and therefore when a single loudspeaker reproduces pure tones with frequencies f1 and f2, it inevitably also produces frequencies like f1-f2 and f1+f2 which were not present in the original.

This "intermodulation distortion" doesn't show up in demos which reproduce single tones, because in that situation it doesn't exist. Even reproducing a the complex tone of a single organ pipe (e.g. a solo reed stop) the issue doesn't have much effect, since all the distorted "intermodulation tones" are actually at the same frequencies as the harmonics of the undistorted tone. But for the very complex tonal structure of real organ music, the cumulative effect of these small unintended sounds is to "blur" or "deaden" the overall effect.

So the bottom line of all this is not to buy the instrument with the biggest selection of nice-sounding stops you can find in your price range, but the instrument with the most sophisticated loudspeaker system you can afford. You might consider that the "advanced" edition of Hauptwerk, which is one of the "standard" software packages for playing pipe organ samples, can produce up to 512 independent channels of audio output. It's unlikely that you need as many independent amplifiers and speakers as that (you would be getting close to the "ideal" situation of one loudspeaker replacing each pipe of your current organ!) but as rule of thumb, more audio channels is better. High quality digital organs in large buildings will often have 40 or 50 independent audio amplifier and speaker channels, not four or five.

There is another consideration here: the "best" design of the physical layout of your audio system is critically dependent on the layout and acoustics of your building. If your proposed organ supplier isn't going to visit your building, measure its acoustic properties, and then recommend one of their standard designs - or better, produce a customized design - consider buying from someone else!