[SBE] audio problem

[A9xw at cs.com]

There are two possible issues, depending on if the station is AM or FM. 
The first, most common, is the harmonic increase exceeds the AM bandwidth 
/peak limits and is causing the limiter to clip the peaks because of excessive 
high frequency content. You have to have a good audio spectrum analyzer or FFT 
device to see the RF spectrum content or base spectrum content so you can see 
the HF content changes between baseband and modulated carrier. The second is 
also harmonic related, if the rise time of the HF content that is increased to 
add bite exceeds the rise time capability of the follow on devices, it will 
cause THD and TIM. Both of these were also a problem with American made boxes 
that performed the same function popular in the 70's. The last is the "phase 
correction" which can cause crest factor issues (peak to average) if in fact it is 
changing the phase of EQ or band separated components that would also change 
the stereo on-air (because of sampling or subcarrier switching) but not be 
heard direct. 

In any event I would first start looking at HF levels baseband vs off-air. 
With follow on EQ and FM's 75 usec pre-emphasis curve, you run out of HF 
headroom and wind up just clipping more and more HF content. Different media requires 
different processing. 

Henry Ruhwiedel