Università degli Studi di Pavia
Centro Interdisciplinare di Bioacustica e Ricerche Ambientali
Via Taramelli 24 - 27100 Pavia - Italy
e-mail : email@example.com
Spectrographic representation of animal
voices has been widely used since the first analogical
analysis instruments (Koenig et al., 1946) were developed
for military acoustic research. The development of digital
signal processing techniques and high-speed hardware at
relatively low-cost has actually made the visualization of
acoustic signals an every-day invaluable tool for
bioacoustic research and for educational purposes.
Low-cost sound acquisition
The basic version allows hard-disk
recording/playback and high-resolution true real-time
spectrographic analysis of sounds up to 22 kHz without the
need of expensive DSP coprocessors or external
Alternatively, the DSPW can be equipped with an Audiologic Audioboard Plus with digital I/O modules which allow a direct digital connection (SP-DIF) with DAT recorders. In this way, sounds are directly transferred from the DAT to the PC, and vice versa, without further Digital to Analog and Analog to Digital conversions, thus preserving the full quality of the recording.
A custom driver developed by Audiologic allows the continuous gap-free real-time DMA transfer of samples between the acquisition board(s) and the computer memory; by means of a specific software and a fast PC, recording/playback with real-time spectrographic analysis and display has been made possible at low cost on signals extending in frequency up to 22 kHz (48000 s/sec, single channel with an i486/66DX2 CPU, two channels with an Intel Pentium P90 CPU). The use of faster CPUs could further increase the performances of the DSPW, allowing, for instance, to increase the overlap factor, to enhance the detail and the smoothness of the display and to add more advanced analysis functions.
Advanced version for ultrasound analysis
The advanced version requires a DSP
(Digital Signal Processor) based acquisition board
(Microstar DAP 2400E/6, made in USA) with 16 analog inputs
and 2 output channels, 12 bit resolution, variable gain,
sampling rate up to 320000 s/sec on a single channel.
Integration with video recordings
The workstation can be further expanded and customized to satisfy particular requirements; by means of an external broadcast-quality video encoder, computer generated spectrographic images can be converted in a standard video signal (PAL or NTSC) to be seen on conventional TV equipments, recorded on a video-tape recorder, or mixed/inserted on live video recordings. This broadcast-quality extension can be positively used to incorporate spectrographic images of sounds in animal behaviour documentary films.
A portable version of the DSPW is actually based on a 16 MHz 80386SX/80387 laptop PC with a 120 Mb Hard Disk, a VGA LCD display, two 8 bit ISA slots holding both acquisition boards, internal battery and external 12 Vcc powering with photovoltaic panels for continuous operation and battery recharge. Due to the low processing speed available on the portable unit, real-time processing is available only throughout the DSP-based acquisition board. A faster portable unit incorporating both standard ISA and PCMCIA slots could dramatically improve the application of digital processing of signals in the field and the integration with other data acquisition tasks such as GPS-based data logging and tracking. Unfortunately such type of instrument is at the moment unavailable on the market and is too expensive to be realized as a custom project.
The DSPW is equipped with its own DOS custom software designed
to acquire, store, edit, analyze and replay signals as
well as analyze them in real-time. Non-compressed digital
signal files can be edited, analyzed and/or played back to
perform play-back experiments (Pavan, 1992, 1994); also,
signal files can be easily red and processed from within
the Matlab environment.
Specific software was also developed to
perform some particular analysis tasks, such a two channel
envelope display, event triggering and direction finding
when searching for sperm whales with the two-channel towed
KOENIG W., DUNN H.K., LACY L.Y., 1946. The sound
spectrograph. J.Acoust.Soc.Am., 18 (1): 19-49.
Page written by G. Pavan, 1994. Updated August 2005.