On Tue,1/19/2016 3:02 PM, Bill Somerville wrote: > all perfectly correct but not normally relevant in the discrete and > finite digital domain. 0dB is normally taken as the output of the > digital source i.e. a digital synthesiser or most commonly an ADC.
In the digital world, the common reference is dBFS, where the reference is to digital clip. The decibel IS a ratio. With no reference, it can only describe GAIN. Any use of dB to define a voltage or power levels without a reference is meaningless. > Any > gain or attenuation from that 0dB level equates to a loss of resolution > with the exception that a stream that, for example, never reaches half > the linear digital amplitude could be amplified by 3dB (multiplied by > two) without losing any information. You're thinking of a signal that is already in the digital domain. I'm thinking of the level of the analog signal that feeds the sound card, and the gain of the audio stage within the sound card that drives the A/D. If, for example, the output of the radio is 2 V p-p and the A/D clips with a 1V P-P signal, setting the input gain of the sound card greater than -6 dB would cause the A/D to clip on peaks. In general, A/D converters get non-linear around their noise floor, so they perform their best as close as practical to digital clip with enough margin that peaks of audio never hit digital clip. In the pro world, that gain margin is often set for 20 dB. And, because of impulse noise in the output of our radios, that's a pretty good starting point. So -- for our 2V P-P signal driving a sound card that clips at 1V P-P, we would want to set the input gain to -26 dB. This is why 0dB is a good setting for an intermediate stage n a digital system because it represents passing the data unchanged. 73, Jim K9YC ------------------------------------------------------------------------------ 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
