Following is a summary of the UNLV's Auditory Perception Laboratory's analysis of vocals that were recorded April 20, 2003, Snohomish County, Washington. The following URL will take you to the National Institute for Discovery Science site where you will find a Narrative of the Event, 2 x WAV Sound Files, and the UNLV analysis.

http://www.nidsci.org/news/acousticanalysis.html

Preliminary Acoustic Analysis of Unusual Large Animal Vocalizations Recorded on April 20, 2003 in Snohomish County, Washington

Summary
At 1:00am on the morning of April 20th 2003, long-time Bigfoot researchers John Andrews, Richard Grover, and Nancy Smith were positioned in a remote location near Stevens Pass in the central Cascades in Washington State. The location was chosen because of a long history of anecdotal reports of Bigfoot in the area, including multiple footprints measuring 20 inches in length, reports of repeated rock knocking and unusual howling and other vocalizations.
Sustained vocalizations from an unknown animal began just after 1:00am. The team recorded several of these sounds using a Sony D-6 recorder with a parabolic reflector for magnification. The cassette recording was submitted to NIDS.
NIDS contracted the UNLV Auditory Perception Laboratory to analyze the vocalizations. Digitization and editing of vocalizations were accomplished using Syntrillium's Cool Edit Pro software. Monaural output from the cassette was digitized at 44.1 kHz (16-bit) sample rate. Any silence preceding or following each vocalization was excised. Similarly all spurious noises that exceeded the maximum amplitude of the given vocalization were excised at zero (voltage) crossing points.
The conclusions of the acoustic analysis are that a human male cannot be ruled out as the source of the vocalizations. According to the report:
However, there are a few unusual aspects of the vocalizations that clearly warrant further investigation. First, the majority of sustained productions are at or near vowel category boundaries, which is very unusual. If these productions were produced by a human male, then an explanation would need to be sought for why the set of vocalizations consistently represent outliers. For example, it is possible for a human to intentionally produce such outliers. It also is possible that such outliers could reflect a limitation in early speech development, such as exceeding a critical period by being raised in isolation. Outliers also could reflect a physiological limitation, such as an anomalous or damaged vocal tract. A second finding that warrants investigation is that many of the vocalizations reflect formants with low center frequencies, suggesting that they may have been produced by a large body. While it is acknowledged that this suggestion at least in part reflects measurement limitations due to reliance on compact spectra with a minimal number of discernable formants, the currently observed pattern of formant dispersion is not conclusively human.
The two acoustic files, labeled "410-418" and "653-702" were recorded from further away according to the researchers. The acoustic file labeled "653-702" provided much of the basis for the formant analysis in the UNLV report.
In addition to contracting for the acoustic analysis, NIDS also contacted the Washington State department of wildlife and secured their database comprising an inventory of the 558 species of known wildlife in Washington.
Finally, because a sound file appeared to bear a resemblance to primate vocalizations, NIDS contacted two nearby primate facilities to ascertain whether any primates had recently escaped from captivity. NIDS was informed by officials at Woodland Park Zoo in Seattle that primates had in fact escaped from the facility several years ago, but all had been subsequently recaptured. Secondly, two primate researchers from the primate research facility of Central Washington University at Ellensburg informed NIDS that all primates (including Washoe) are presently accounted for and none have ever escaped.
The full NIDS report contains: (i) this report summary, (ii) the full narrative from John Andrews, Rick Grover and Nancy Smith relating the events and circumstances around recording the vocalizations, (iii) two acoustic files containing representative samples from the vocalizations that can be freely downloaded and listened to. All sound files are copyrighted to John Andrews (iv) the full report on analysis of these vocalizations from the acoustic lab, and (v) the Washington State wildlife database.
The purpose of this NIDS report is to invite interested wildlife researchers to download the sound files and compare them with known wild life vocalizations, especially those found in the Washington State wildlife inventory. The NIDS report can be found in the "Research News" section of the NIDS web site at www.nidsci.org. Feedback can be sent to NIDS via e-mail: nids@anv.net, telephone: 702-798-1700, or fax: 702-798-1970.