Sorry, but I must disagree with you.
If I take a 20 Khz
sine wave, and sample it every 0.2 mS (5 KHz rate) then all samples will be at the same
point on the wave, and the result will be a
flat line. 100% of the information would be lost. It would also be impossible to distinguish between a 20 KHz, 10 KHz, and a 5 KHz wave, as they would all be
flat lines. Similarly, if sampled at 20 KHz the result for a 20 KHz wave would be the same. Which is why Mr. Nyquist (along with Mr. Shannon) say that you need to sample at 2x the frequency.
Now, are you perhaps confusing this with the encoding rate? That can certainly be (and these days often is) considerably less than the sampling rate.
Edit: Also, your typical sampling systems have a Nyquist (there he is again) filter before the sampling
stage, so your 5k sampling should have a 2.5k filter... to prevent things like a 6 kHz signal sounding like a 1 kHz signal.
-Fred