I wish NOAA had those recordings at real speed instead of sped up 10 times. 52Hz is well within human hearing, it's a G#, 4 frets up from the bottom of a typical bass guitar. Typically the big whales are around the C that would be past the left end of the piano and beyond human hearing.
From the paper, there is an interesting statement about the capability of the Navy hydrophone systems:
The lack of calls before and after tracking periods appeared to be because the whale was not producing calls, and not due to the lack of the ability of the monitoring equipment to detect the sounds. As the tracks demonstrated, the monitoring system was not limited geographically, and appeared to detect these calls, usually on multiple arrays, whenever calls were produced in these deep-water regions.
The sample rate is 8kHz, which means the Nyquist frequency is 4kHz. Slowing it back down won't sound good, but frequencies below 400hz will be present.
Fortunately the US Defense Technology Information Center has liberated a copy: http://www.dtic.mil/dtic/tr/fulltext/u2/a429410.pdf
I wish NOAA had those recordings at real speed instead of sped up 10 times. 52Hz is well within human hearing, it's a G#, 4 frets up from the bottom of a typical bass guitar. Typically the big whales are around the C that would be past the left end of the piano and beyond human hearing.
From the paper, there is an interesting statement about the capability of the Navy hydrophone systems:
The lack of calls before and after tracking periods appeared to be because the whale was not producing calls, and not due to the lack of the ability of the monitoring equipment to detect the sounds. As the tracks demonstrated, the monitoring system was not limited geographically, and appeared to detect these calls, usually on multiple arrays, whenever calls were produced in these deep-water regions.