Going Digital: The 1960s - IEEE Global History Network

JAMES KAISER: That got me very interested in signal processing. Now, at the time
I arrived at Bell Laboratories [ca. 1960], a change in the means of doing research
in the speech area, in the coding area, was under way. Instead of the old way,
which was to test an idea about a new way to do things by designing the electronics
that embodied that idea and then running tests on that physical embodiment,
we were starting to simulate the system-a compression system, an encoding
system, whatever-on the general purpose digital computer. Then we would just
run a test of the new idea, taking speech and running that through the simulated
system and listening to the result. It was much faster and more versatile.
So I got much more interested in how you took continuous systems and
got the discrete models necessary for the simulation. With my control background,
I knew continuous systems and filter design quite well, and I tried to
carry over some of the same ideas to the discrete world. A lot of it carries over
as far as the recursive filters are concerned. These design techniques carry
over directly via the different transform techniques, the Z transform, the
bilinear Z transform, the matched Z transform, and so forth. But one feature of
the digital systems is that it's very easy to build finite impulse response digital
filters, whereas these are very difficult to build as continuous filters. 1o
JAMES KAISER: The thing was, there were old timers-especially in industrythat
had been designing filters, continuous filters, for years, and all of the sudden
these fellows were told, "Now look, I want you to build digital filters." Their
reaction was, "I don't know what a digital filter is." They were completely lost
and some of these fellows didn't want to learn the new stuff. They said
''There's too much new to learn! Don't bother me with the new stuff." So one of
my goals was to preserve all the knowledge that those fellows already had
and say to them, "Look, all you've got to do is run this little program with that
knowledge you already have and it will design a digital filter for you. You know
how to do it!" That's basically what the bilinear transformation does. It carries
the continuous filter designs over to the discrete design. 11
Yes, radar processing, and you also found sonar people interested.
That was the group for serious applications [in the 1960s]. It was a serious
application because people actually built it to put in systems for that purpose.
Speech, I think at that time was mostly in the research stage, but they
did have an application goal in that, too.
... I think signal processing is becoming so popular for two reasons. It is
application-driven, particularly as seen now, and it is very much tied with technology.
So you can identify applications; you have needs to actually build systems
to do certain tasks. 12
BEDE Llu:
lJames Kaiser oral-history interview 11 February 1997, pp. 6-7.
2James Kaiser oral-history interview 11 February 1997, p. 24.
3Bede Liu oral-history interview 10 April 1997, pp. 20-21.
72