Dave and Parks-
I agree with both of you, but I just came across this while searching and passed it along for what it's worth. (Which I will admit is a bit dubious, since it does sound a bit "rough" to say the least !)
Also, might it be possible that Phillips might have been sending a bit slower than usual in the hopes the signal might have been more easily understood ?
I have always assumed the sound in ANTR was fairly accurate. I would also assume that since those earphones were not exactly "hi-fi" that they would have had a "tinny" sound.
In reference to the 400 HZ tone, when I was serving as an ET aboard CVE-118 during the Korean Conflict, one of my assignments was on a Radar which used a rotary spark gap as the modulator.(I believe it was a Model SP Radar.) The tone, as I remember, was also around 400 HZ and you could observe the spark through a small inspection window.
Years later, I attended a "Ham Radio" Convention. One of the displays in one of the booths was a "name that tone" contest. Somehow I overlooked the booth, but one of my colleagues won the contest...he was also a former ET in the USN....the frequency of the tone was 400 HZ of course !
73, Robert