HF Sonar on subs

[Wim Libaers]

Originally Posted by Sonoboy

That tonal generator that HydroShok posted is not an accurate way of determining what frequency you can hear at.

Unless I really can hear a sound at 181,019.34 Hz...

That is a frequency well above the limits of most soundcards, and sound drivers. What happens is that the program will sample a sine function of that frequency at intervals that are longer than a period of the function, causing aliasing and a signal that appears to have a much lower frequency.

Try this applet:
http://www.dsptutor.freeuk.com/aliasing/AD102.html
It is set to 8000Hz sampling frequency. Put checkmarks on "Input signal" and on "Sample points" or on "Alias frequency". Put in a value below 4000 Hz and click plot. They will be the same. Then try higher values. You'll notice differences. The rules can be found here:
http://www.dsptutor.freeuk.com/aliasing/AliasFrq.htm
If you know the sampling rate the tone generator uses, you can calculate which frequency really came out of the speakers.