On 20/01/2016 00:53, Joe Taylor wrote: > Sure, we could set the level higher. WSJT-X works OK with the noise > level set anywhere between about 20 dB (rms=10) and 60 dB (rms=1000). Hi Joe & all,
so it will be interesting to for Mike to report back what difference he sees now he has removed what appeared to be ~60dB digital attenuation from his system and probably a downstream ~60dB digital gain to compensate. I will try and summarise a couple of points: a) having the ADC clipping due to excessive audio level is bad, once the sampling circuit is driven to the maximum count it is no longer linear and cannot express the cumulation of the many cosine waves that are the signals and noise. Jim points out that the peak levels from radio receivers are often impulses so the slow modes like JT9 and JT65 are very tolerant of short duration sampling non-linearities but we are still better off without them. We should strive to feed just enough audio level to the ADC but not too much. b) Joe points out that the one LSB quantization error of the ADC is swamped by the receiver and band noise but if we have our input audio level to low and have to apply digital gain after sampling to get a usable signal then for every dB of digital gain applied we are increasing that quantization error by the same amount. That's is OK up to the point where the quantization error is no longer buried in the noise, then a threshold is crossed and the wanted signals have their signal to noise ratio reduced. 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 [email protected] https://lists.sourceforge.net/lists/listinfo/wsjt-devel
