Interpreting MicPeakData Values

Peter K1PGV

I'm having trouble making sense out of the MicPeakData values I'm getting from FlexLib. I'm hoping that somebody can shed some insight in terms of what this value is actually reporting.

If I send, via DAX, an steady sine wave (mode = DIGU, so there's no compressor activity)... I will get two rock-steady values for MicData and MicPeakData.

For example:

MicData: -0.6

MicPeakData: +3.28

I initially figured MicPeakData would be rapidly changing "peak" VU meter type data and MicData to be more of a smoothed (damped) value. But this clearly isn't what's going on.

My question is: What the heck is MicPeakData telling me?  MicData at -0.6 looks "right" to me, as it appears to result in the power output I would expect.

The "Level" meter in SmartSDR appears to be showing MicData, if that's helpful at all.

Eric-KE5DTO

The MicData is in units of dBm (power).  It is the area under the curve.  This is a sum of the squares kind of value.

The peak value is in dBm (voltage).  It is literally the highest voltage sample since the last peak was sent -- as close to instantaneous as you are going to get in this system.  

Peter K1PGV

Thank you, Eric.  Much appreciated!

But I'm not sure what that implies, in terms of use of these values.

If I pump a steady sine wave into the radio, and get a steady MicPeakData value of 3.28 and a MicData value of -0.6, is that signal clipping or not?

I *think*, if I understand what you just explained to me, that this signal would be clipping.

Thanks again,

Peter K1PGV

Eric-KE5DTO

The hard and fast answer is that you should shoot for no peaks over 0 dBm.  There is actually another 2.5dB of headroom above 0 before clipping begins, but full calibrated output power is achieved when the peak is at 0.

Peter K1PGV

Thank you.  That's abundantly clear.