HF Sonar on subs

[Zerogreat]

It depends on speakers, some behave strangely when they have to play sounds that are off their limits

[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.

[HydroShok]

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...

yeh, i just noticed that too. its a bug or something. Thats way overkill for a frequency anyways, i doubt it was designed for it. That, and if a soundcard could put out 181khz A/C to an antenna, you'd have a radio transmitter. The FCC is pretty nazi about that type of stuff. Once it gets above 30k, my speakers make wierd noises up and down in pitch. But its cutoff range is supposed to be 20k anyways

put it 10,000hz play the tone, then press increase button, it should fade out big time near 20khz, and then it returns at 30k but thats cuz the aliasing mentioned above i guess.

[LuftWolf]

Originally Posted by *[FOX

* Bort]The HF sonar can be very useful in close quarters when you need a quick target ID, I've used it a few times to ID surface ships but never subs. Probably not too realistic...

Perhaps it is realistic... some civilian and commerical HF sonars give almost a photograph of things like underwater wrecks and topography.

[MaHuJa]

In the game, I believe the sphere sonars can hear frequencies up to 2kHz. Most pings are above that.

Torpedo ping frequencies should be changed by the doppler effect - I don't think they really do that in DW. Though I haven't paid too much attention to the frequency readout in active intercept.


As for the shipmounted HFAS, I remember speculation that they may be operating up in the 75kHz area or something - though that's pure speculation, and it might even be possible to prove it wrong.
If you can identify ships by it, either you're really good at recognizing their undersides, they're sunk, or there's a bug. You should never be able to see anything above the water.

I believe that the current sonar engine, with its passive/active intercept split, would be detecting HFAS at the full ~20nm(?) it detects all other active sonar at.


On the matter of what your computers can output, the two sample rates commonly in use are 44100 and 48000. The highest frequency it can output cleanly is half of whichever is active.

Also, while most speakers claim a 20-20000 frequency range, none of them (that I've seen) document the signal loss at the extreme frequencies.


(Oh, and, I don't think the FCC controls a 140khz signal if it is of an acoustic nature... Only the EM, which most speakers, made as they are, would radiate while at it. I don't expect air to carry such an acoustic signal for a whole 1mm, however.)