Dynamic Range


This is a measure of the range of signals that a sound card can handle. It's important because while you are trying to listen to a weak signal there may be other signals in the band pass that are huge, and one does not want those huge signals from keeping us from listening to that weak signal.

If a signal exceeds the range that your sound card can handle (overloading) then we see signals all over the place that are really not there, these signals can often wipe out signals that we do want.

It's a little complicated and a visual display will help to understand it, so I will be looking for an illustration.

But dynamic range involves more than just than the ratio of signals a sound card can receive (bits of resolution) it also involves matching the gain of the radio to the voltage range of the sound card.

Lets say your SoftRock can put out a signal that is is 4V peak to peak or 1.4V RMS that is +16dB and you have a sound card with 100dB range so theoretically you could also hear a signal at -84db (not so good) but you really won' experience that why?

First your sound card most likely can not handle a signal so large so you will overload it, so you need to adjust the gain of the radio by 6 dB so the 10dB input to the sound and does not cause an overload, those dB don't just disappear, your card still has a 100dB range so now your radio works from +10 dB to -90dB still lousy but better.

So what happens if the radios gain is increased by 10dB the bottom goes down by 10dB to -94 dB but your upper end suffers by 10dB, remember the total range is 100dB so now your radio can hear a signal that is -94 and overloads past +6dB, that is still pretty deaf. So we increase the gain so it can hear a -120 dB signal but then our top end is -20dB, that is where the SoftRocks are, they can hear pretty good but can't handle large signals without outside help.

What would happen if you had a shoddy 16 bit card? your dynamic range might only be 80 dB so you have a range of -20dB to -100dB, weak signals (-110dB) are not there, on a 24 bit card with 100 dB of dynamic range that signal is fine and clear.

By adjusting the radio's gain we can maximize the performance of the radio, on 80M the average noise is about -100dB so what is the point of having the radio be capable of receiving a -120dB signal? none, we are wasting our dynamic range, if we tweak the radio so it has enough gain then we could receive from -103 dB to -3dB and we don't loose any signals, we lost nothing on the bottom end but gained 17dB on the top end.

Moral of the story, get a 24 bit card they have a larger dynamic range which translates into hearing weaker signals while tolerating strong signals.

A Delta-44 has 99 dB of dynamic range
A Edirol FA66 has 109 dB of dynamic range
The Atlas/Ozy/Janus has 111 dB of dynamic range

More details later and some pictures.