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Author Topic: PowerSDR gets a downward expander  (Read 3162 times)

W4TME

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PowerSDR gets a downward expander
« on: August 05, 2009, 07:24:34 AM »

Another innovation has cropped up in FlexRadio's PowerSDR software - a downward expander to augment the noise gate function.  They are the first to have this feature in a ham radio.  A downward expander (DE) is an enhanced type of noise gate. I never have liked the way traditional noise gates sound for voice applications due to the instantaneous way they operate.  It chops up your audio too much.

The DE provides what is known as a "soft knee" where the transition from closed to open isn't so abrupt (off/on) so that the "pumping" is no longer a problem.

The function of a good downward expander is to increase the apparent dynamic range of the system by decreasing the gain during the relatively quiet times thereby moving the apparent noise floor downward. It does this by comparing the signal level to a threshold. When the signal level drops below this threshold, the downward expander *decreases* the system gain by some ratio.  A noise gate on the other hand, does not decrease the gain but abruptly switches it completely off below the threshold level.  A noise gate is a DE at it's most extreme setting where the slope (gain reduction ratio) is infinite.

This new DE feature is currently in a final test mode (available via SVN) and should show up in a released version of PowerSDR sometime this fall.

This is just another reason software defined radios have a technical and "future proof" edge over legacy DSP / analog hybrid and the less flexible firmware or "ridigedware" defined radios.  My true software defined radio just keeps getting better! I love it!

-Tim
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