Digital signal processing is an important subject in many aspects of modern music making and it has important uses with Hammond Organs. What exactly does it mean?
First of all, it's a very big subject and encompasses many other categories besides electronic music. For our purposes regarding Hammond Organs, we're only concerned with its application to musical instruments and we might be more accurate in referring to it as digital effects processing.
Prior to the days of the first Hammond organs in 1937, organs were pipe organs, and most of them were installed in halls and churches, instances where the instrument was in a fairly large room. The naturally occurring reverberation in these large rooms and halls added a lot to the overall big sound of these instruments, and it also complemented singing and other instrumental music as well. When the Hammond appeared, its inventor, Laurens Hammond envisioned an instrument that would be a lot smaller and less expensive than a large pipe organ but he still intended for his instruments to be used in places where traditional pipe organs were found.
The much smaller size of the Hammond, plus its ease of installation, however made it possible for Hammonds to be installed in much smaller rooms, such as rooms in ordinary houses and apartments. Its much lower cost also made it affordable for many homeowners. All of a sudden, if you wanted an organ-like instrument in your home, it was possible now to have one. Unfortunately, these smaller rooms lacked the reverberation of large halls, and Hammond quickly found out how important at least some degree of reverberation was to the sound of his instruments. Whereas in a hall the Hammond of 1937 could sound quite majestic, in the confines of a living room with a carpet on the floor, the sound was somewhat lifeless and dead. This was not the fault of the instrument, but the fault of the room. Ordinary home-size rooms simply do not have the capability of producing the type of reverberation that enhances music.
Laurens Hammond's approach was to have his engineers create some kind of machinery that could make reverberation without needing lots of room, which they did succeed in doing by using a network of coil springs. See the Hammond Article for details. Other improvements to the Hammond to add more audible excitement to the basic instrument were the addition of a chorus generator to some models and also the use of the Leslie Speaker and in certain cases tape echo would be added as well although the Leslie speaker was not a Hammond product, and Laurens Hammond did not like them and adamantly refused to allow the use of Leslie speakers with his Hammond organs. Likewise, tape echo was a studio effect and not supplied by Hammond either, although I have never been able to find out what Hammond actualy felt about tape echo. But his dislike of Leslie speakers is well documented..
Until the 1980s, these and other enhancements were in widespread use. Today, that great musical combination, a B3 Hammond with a 122 Leslie and a PR40 Hammond speaker cabinet is still a very much sought-after package, often selling for several times what it was worth originally.
Digital signal processing as we at the NSHOS use it is the modern substitute or replacement for all of the above, namely, reverb, echo, Leslie speakers, and a host of other effects that enhance either the Hammond or other instruments that we use. The advantage of digital signal processing is that it is fully programmable, in many cases works better than the earlier technology, and is also now a lot less expensive and requires very little physical room. One of the biggest plusses about digital signal processing is the incredible flexibility or number of options that it makes available.
Let's look first at reverberation. Initially if you had a Hammond in a home, you either made do with virtually no reverberation at all, or else you relied on the reverberation equipment that Hammond included in a lot of their equipment. If you used a Hammond PR40 speaker cabinet, you got a fairly decent reverb effect from the so-called necklace reverb unit that was included. If you wanted some control over the reverb, you could vary the volume of the reverb relative to the volume of the direct signal from the Hammond, but that was it. If you wanted a reverb that took more time to trail off, or if you wanted a "smaller" sounding reverb that decayed very quickly, it was not possible. If you had one of the earlier Hammond reverb units with the springs in oil, such as was found in HR40 and DR20 speaker cabinets, you got reverb on the bass and mid range and almost none where you need it most, in the treble range. You also got a reverb that was very uneven, making some notes boom out and others appear to be too quiet. Still it was better than no reverb at all, but not much!
Enter Digital Signal Processing. Now you could get all kinds of reverb, and in stereo too. If you wanted to simulate a large hall, you could do it. If you wanted a smaller room, this was easily possible. If you wanted to get the effect of a room with a pronounced echo as well as a reverb, tweak the controls of a digital signal processor, and you had that as well. If you wanted to simulate a room with a lot of acoustical treatment where the high frequency reverb decayed quickly and the lower frequency reverb lasted longer, this was possible too. If you wanted a reverb that began to build up after a few milliseconds of almost complete silence, just add a little pre-delay. Want the reverb to give the illusion of being far away from the musical instrument or being up real close? Just make a few minor parameter adjustments and the reverb will take on almost any quality you want. And this is just reverb.
It is no wonder then, that digital signal processing has become as important to modern music making as MIDI, if not even more important. So how exactly does all this wonderful, neat stuff work? Go to the next page as we begin a little overview of digital signal processing.