Università degli Studi di Pavia

Centro Interdisciplinare di Bioacustica e Ricerche Ambientali

The history of the CIBRA Digital Signal Processing Workstation

Before the establishement of the Centre in 1989, bioacoustic research has been carried out at the Institute of Entomology. The activities began in 1980 with the developement of a computer based digital spectrograph. The first one in Italy dedicated to the study of animal vocalizations; it was developed within my thesis for getting the degree in Natural Sciences.
The system was based on a desktop computer Tektronix 4052 (64K RAM, 300K tape storage, monochromatic graphical screen - the famous Tektronix storage tube, fast Basic interpreter in ROM) interfaced (IEEE-488) with a Bruel & Kjaer 2033 spectrum analyzer (10K samples memory, 12 bit AD converters, maximum sample rate 51200 samples/sec to get 20kHz bandwidth, 1024 points FFT, real-time display up to 2kHz) for signal acquisition and analysis. The system also included a disk unit Tektronix 4907 (three 5" floppy disks, 630K each), a Tektronix 4611 hardcopy unit (black & white, no shades) and a Tektronix 4663 plotter. The sound source was a portable open reel recorder SONY TC510-2.

From left to right: Tek 4611, B&K 2033, Tek 4052, Tek 4907, Tek 4663

Printout of a bird song (1981). The image is made by assembling 6 screen hardcopies (3 for the spectrogram, 3 for the modulation curves).

In 1985, after getting the degree in Natural Sciences in 1983, the programs were rewritten in FORTRAN on a HP 1000 (128K RAM, 5MB removable HD, 10 bit AD converter, 512x512 pixels color graphic display) made available by the Dept. of Electronics of the University of Pavia. I am very grateful to Prof. R.Schmid, chief of the Department in that period, for having allowed me to use all the instruments without any restriction. That powerful instrumentation allowed the development of several new procedures, including continuous signal acquisition and HD recording, easy and fast signal retrieval and display, colour spectrograms, color manipulation on displayed images, wider control on analysis parameters, moving cursors to take measures on the spectrograms (time, frequency and dB readings), and, overall, speed! Few minutes to get a 0.625s spectrogram! While developing software on that system, I had the honour to see at work a Laben computer with 16Kbytes of "ferrite doughnut" RAM, a paper tape reader for programs and data I/O, an oscilloscope for graphical output.

Envelope display for signal retrieval and colour spectrogram of a signal frame (1985).

The emerging Personal Computers, even if limited in their performances and very expensive - more expensive than a car -, suggested me to start developing a personal sound analysis system.
The very first attempt was in early 1986 with a wonderful Sinclair QL (QL meant Quantum Leap...); small, thin, black, lightweight, with 128K of RAM and a Motorola 68008 inside. Its powerful procedural Basic in ROM allowed the first experiments and the development of a skeleton of the new software. Very soon, I switched to a Pascal compiler and a 68000 Assembler to get speed. I rewrote the programs; they worked fine on synthesized signals, but, unfortunately, I never bought an AD converter to work with real sounds.

Spectrogram of courtship sounds emitted by the goby fish Padogobius martensi made on a 8086 PC (1986)

Rewriting the whole software, as well as optimizing it for the new hardware, was a big challenge. I spent a lot of time to make it running. I was very lucky to find a wonderful book ("8087 Applications and programming for the IBM PC and other PCs" written by R.Startz, published by Brady in 1983) and after reading it I gave a boost to the software by writing most of the critical routines in Assembler 8086 and 8087. Then, the shell of the program and the user interface were written with the Microsoft Basic Compiler and subsequently with Microsoft QuickBasic, one of the first compiled procedural Basic available for PCs.
The writing of a well optimized FFT routine in assembler was not a trivial task and the results were slower than expected. Again, I was lucky enough to find a highly optimized assembler routine written by John Hartwell to be linked to FORTRAN programs and I adapted it to my needs. I really spent a lot of time writing, optimizing, compiling and linking programs in three different languages. Some years later I contacted again Mr. Hartwell to ask him for updated routines and he replied: "I no more write computer programs. In the life there are lots of things to do better than programming." Good reply. Now, several years later, I really understand the meaning of that answer.
At the end of 1986 the PC system began to work well. New important features were developed: DMA based continuous recording and playback, variable rate playback, editing and synthesis capabilities, 16 colour spectrograms on up to 16K samples on screen or continuous spectrograms (continuous sheet) on inexpensive dot matrix printers (with multipass printing to produce gray shades), frequency tracking and song parsing.
In 1986, the first system running on a 8MHz 8086+8087 required about 20 minutes to display a 16 colour spectrogram on 16K samples. A bit later, in 1987, computation times were slightly shortened by switching to a 12 MHz 80286+80287 and then to a 20 MHz 386+387.

With this new system I began to work extensively on many animal species, including marine mammals. Also, I began to experiment with song parsing, frequency tracking and automatic analysis of song parameters. The very first attempts were very successful because I tested the algorithms on very good recordings of relatively simple songs... though, I discovered very how much complex "real world recordings" can be...

Spectrogram printed with a simple dot matrix printer (1987).
The software allowed to print continuous spectrogram on inexpensive continuous perforated sheets.
Shades of gray were produced by multipass printing.