I remember watching this event on television in 1969 and decided to look into this myself, since the original audio is posted at the NASA website. I remembered the quote as "That's one small step for man, one giant leap for mankind."
By the time I began looking at it, the news stories were out of control, substantially misrepresenting even Mr. Ford's own claims.
Mr. Ford used $45 GoldWave software and only looked visually at the section in question, after applying some simple background noise filtering.
As everyone who has listened to the clip knows, there is a bit of crackly static, perhaps microphone noise, or some other transients during the "for man" section in question. Mr. Ford filtered the entire audio clip based on selecting the background noise profile when Mr. Armstrong was not speaking. This produced a much more noise-free recording, but only reduced, and did not eliminate the noise transients in question.
I utilized $400 Adobe Audition 2.0 audio production software (developed by Syntrillium Software, which company Adobe bought), and $700 Celemony Melodyne Studio 3.0 software to do my investigation, so I had somewhat better tools at my disposal, in addition to my experience with audio in the recording studio environment and my career in electrical engineering.
Mr. Ford's conclusions have also now been disputed by some prominent linguists and human speech experts, such as Dr. David Beaver, a professor of linguistics at Stanford University, and Dr. Mark Liberman, a professor of linguistics at the University of Pennsylvania, the former also aided by contributing material from a number of people, including Mark Tiede, who is both on the staff of the Speech Communication Group at the Massachusetts Institute of Technology and is a Senior Scientist at Haskins Laboratories, Professor Suzanne Boyce, who is a linguist and clinical Speech Pathologist at the University of Cincinnati, and Professor Lisa Davidson, a Phonetician/Phonologist at New York University.
Mr. Ford's conclusions have also now been disputed by Eric Jones, editor of NASA's own Apollo Lunar Surface Journal (ALSJ), Colin Mackellar and the personnel managing the former NASA Honeysuckle Creek Tracking Station in Australia, which also received the audio transmissions from the moon and have separate recordings, including Mike Dinn, who was actually on that team during the Apollo 11 mission in 1969.
I have analyzed the audio provided by NASA from the Goldstone Tracking Station in California, the audio provided by the Honeysuckle Creek Tracking Station in Australia, and the audio posted by the Parkes Observatory in Australia, all using more advanced methods and analysis than Mr. Ford. None of these recordings reveal any evidence of a spoken "a" in their recordings.
The following 4 page paper (1 page text, 3 screen shots) provide a succinct summary of my findings on the NASA provided audio which was broadcast in 1969 (based on Goldstone transmissions at that particular point in the mission):
One_small_step_for_man_reaffirmed.pdf
Additional links are provided in that document, as well as below:
Internet archive of Peter Shann Ford's website Internet archive of Peter Shann Ford's paper The original audio clip from the NASA website Filtered version, to remove background noise Filtered version, stretched 10x Unfiltered version, stretched 10x Filtered, stretched 2x Unfiltered, stretched 2x Original from Honeysuckle Creek Honeysuckle, stretched 10x Original from Parkes Observatory Parkes, stretched 10x
6/03/2009 update: The following audio was supplied by John Stoll at NASA Houston, which I obtained through Dr. Christopher Riley, an author collaborating and contributing to the upcoming Cheltenham Science Festival in the U.K.