Digital Signal Processing
Digital signal processing is another topic that we at NSHOS sometimes mention. What exactly does it mean?
First of
all, it's a very big subject and encompasses many other categories besides
elect-ronic music. For our purposes at NSHOS, 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 also in certain cases
tape echo would be added as well although the tape echo was a studio effect
and not supplied by Hammond.
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.
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