TECHNICAL INFORMATION ON THIS PUBLICATION
[Following is the technical information summary included in the original 1994 production of this compendium in Word Perfect.]
The Text
This publication was produced by using Word Perfect 6.0 for Windows (Word Perfect Corporation), running under Windows 3.1 (Microsoft Corporation) on a 80486-DX2 66mhz personal computer using MS-DOS 6.2 (Microsoft Corporation). The hypertext feature of Word Perfect 6.0 was used to create the links among the various files and sections of text. The Object Linking and Embedding (OLE 1.0) features of Word Perfect and Windows were used to embed the sound files of bird vocalizations.
All text files are in READ-ONLY format. Although they can be readily changed like any text file under a word processor, changes can only be saved under another, user-supplied file name, thereby preserving the integrity of our original files. We request that any desired changes, edits, or corrections in the text files be sent directly to the senior author for updating future versions, and that the original files not be altered. We realize that electronic files are easy to edit, but this request is tantamount to asking that a buyer of a book does not tear out pages and rebind the book with their own text. Instead, we suggest that the user write their own separate supplements to this publication, if so desired.
The Sound Recordings
Bird vocalizations and sounds were recorded in the field by the authors and others (see Acknowledgments). The authors used a portable, battery-operated Sony casette tape recorder with audio microcasettes and a built-in microphone. The senior author then further processed the recordings as follows.
Step 1. Editing for individual sounds.--The individual species' sounds were extracted and transferred from the field recordings line-to-line onto standard-sized audio casette tapes.
Step 2. Audio digitizing.--The recordings were then fed by direct line from the audio casette tapes to an EISA-bus 80486-DX2 66mHz personal computer, into a Sound Blaster 16-Bit Advanced Signal Processor Audio Card (Creative Labs, Inc.) to create digitized-sound Wave (.WAV) files. Individual Wave files were created for each sound. Most files were digitized in 8-bit mono mode at an 11-kHz sampling rate. These settings retained the characteristics of the sound but helped to keep the sound files as small as possible. A few sounds, such some high-frequency calls and songs of sparrows and warblers (e.g., see orange-crowned warbler call "a"), were digitized in 16-bit mode at a 22-kHz sampling rate to enhance their sound quality. Such 16-bit recordings at high sampling rates of 22-kHz and above take up substantially greater file space even if saved in compressed format. Sampling rates were chosen to optimally balance three variables: maintaining sound content and quality, minimizing file size, and avoiding sound aliasing (misdiagnosing the shape of the sound wave).
Step 3. Audio cleaning.--The .WAV digitized sound files were then further edited to delete superfluous sound defects (such as pops and clicks), by using Sound Blaster's CTWAVE Wave Studio Ver. 1.1 running under Windows 3.1.
Step 4. Audio filtering.--Next, the sound files were filtered of extraneous underlying noise by subjecting the files to noise-reduction Fast Fourier filtering algorithms, by using EZSound Wave Ver. 2.01 (Future Trends Software, Inc.) running under Windows 3.1. The filters included:
o Lowpass 50%, where frequencies above one half of the Nyquist (or one quarter of the sampling rate) were removed. For example, a sound recorded at 44,100Hz will have frequencies above 11,025Hz removed. This filter is a sixth order Butterworth filter with a cutoff at 0.47 of the Nyquist frequency.
o Lowpass 25%, where frequencies above one quarter of the Nyquist (or one eight the sampling rate) were removed. For example, a sound recorded at 44,100Hz will have frequencies above 5,512.5Hz removed. This filter is a third order Inverse Chebyshev filter with a cutoff at 0.25 of the Nyquist frequency and stopband 15dB down from passband.
o Highpass 25%, where frequencies below one quarter of the Nyquist (or one eight the sampling rate) are removed. For example, a sound recorded at 44,100Hz will have frequencies below 5,512.5Hz removed. This filter is a third order Inverse Chebyshev filter with a cutoff at 0.25 of the Nyquist frequency and stopband 15dB down from passband.
The two Lowpass filters were useful for screening out extraneous high-frequency noise and unwanted sounds, such as filtering out background high-frequency songbird calls and songs, from the desired calls or songs of species with lower frequencies, such as owls. The Highpass filter was useful for screening out extraneous low-frequency noise, such as lower-frequency recording hiss, from the calls or songs of most of the Oscine songbirds, retaining their high frequencies in the sound files. Some sound files were deemed "clean" enough to not warrant any additional frequency filtering. Filtering was not used if it sampled out any of the original frequencies of the target sound, even if it served to reduce background noise.
Step 5. Volume equalization.--The volume (amplitude) of each .WAV sound file was then adjusted by using the EZSound Wave program. This volume maximization algorithm searches each sound file for the maximum percent that the volume can be increased without distortion or clipping errors. This volume is then applied to the entire file. If the percentage is above 2000% or equal to 100%, no changes were made. This ensures that all sound files are consistent in volume.
Step 6. Sound object embedding.--Finally, the filtered and volume-adjusted .WAV sound files were included as embedded objects in the text files of vocalization descriptions by using Word Perfect's 6.0 OLE (Object Linking and Embedding) Object Inclusion feature.