On 20/01/2016 14:24, Michael Black wrote: > Isn't that all digital gain? Wouldn't you want that closer to zero? > I see the ingain getting passed to symspec and hspec_ so what is the > purpose of changing the scale inside symspec? > Does this linear rescaling in symspec really matter? Hi Mike,
the gain slider ranges from -50 to +50 so the middle is zero. Yes the scaling matters for the waterfall and spectrum plot. It is applied to the sum of the squares of the samples before calculating the overall RMS power for the thermometer meter. It is also applied to each waterfall/spectrum bin in the frequency domain before the flattening algorithm is applied. I do not think either of the above are linear adjustments, they both amount to multiplication I believe. OTOH the decoder gets whatever arrives in the audio stream, no gain adjustment is made, so if you are having to move the WSJT-X gain slider up above half way to get a power/waterfall display then you are probably not providing enough level to the ADC, or as in your case you are dividing the samples in the digital domain. Either way you are increasing the quantization error contribution to the signal to noise ratio of the wanted signals. Depending on the AGC capability of your rig or, the way you have set the RF gain if you disable the AGC, you need to maximize the level to the ADC but keep it short of clipping. The output of the ADC should not be attenuated with a digital volume control as that decreases resolution and increases errors for no benefit whatsoever. As I said above, there is no point dividing the samples (reducing the volume) in any intermediate digital stage as it will reduce the resolution and increase the quantization error contribution. 73 Bill G4WJS. ------------------------------------------------------------------------------ Site24x7 APM Insight: Get Deep Visibility into Application Performance APM + Mobile APM + RUM: Monitor 3 App instances at just $35/Month Monitor end-to-end web transactions and take corrective actions now Troubleshoot faster and improve end-user experience. Signup Now! http://pubads.g.doubleclick.net/gampad/clk?id=267308311&iu=/4140 _______________________________________________ wsjt-devel mailing list wsjt-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/wsjt-devel
