Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
The three frequency groupings used in the study
| Group 1 | 404 kHz | 104 kHz | 26.7 kHz | 6.9 kHz | 1.8 kHz | 450 Hz | 117 Hz | 25 Hz |
| Group 2 | 636 kHz | 164 kHz | 42 kHz | 10.8 kHz | 2.8 kHz | 714 Hz | 184 Hz | 34 Hz |
| Group 3 | 1000 kHz | 257 kHz | 66 kHz | 17 kHz | 4.4 kHz | 1.1 kHz | 289 Hz | 74 Hz |
